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Tapping the Potential of Urban Roof Tops

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Tapping the Potential of Urban Roof Tops

Tapping the Potential of Urban Roof Tops

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    Tapping the Potential of Urban Roof Tops Tapping the Potential of Urban Roof Tops Document Transcript

    • Final Repor tTa p p i n g t h e P o t e n t i a l o f U r b a n R o o f t o p sRoof top R e so u rce s N e igh borhood A s s e s s m e nt October 31, 2007 D E S I G N , C O M M U N I T Y & E N V I R O N M E N T
    • Final Repor tTa p p i n g t h e P o t e n t i a l o f U r b a n R o o f t o p sRoof top R e so u rce s N e igh borhood A s s e s s m e nt Bay Localize is an Oakland-based organization that catalyzes a shift from a globalized, fossil fuel-based economy to a localized green economy that strengthens all Bay Area communities. Bay Localize is a nonprofit project of the Earth Island Institute. This report is generously supported by the Community Foundation Silicon Valley, Laurence Levine Charitable Fund, San Francisco Foundation, Ollie Fund, and Bay Localize supporters. It was prepared by Brian Holland and Sarah Sutton of Design, Community and Environment, Kate Stillwell of Holmes Culley, and Ingrid Severson and Kirsten Schwind of Bay Localize. For more information, contact: Bay Localize 436 14th Street, Ste 1127 Oakland, CA 94612 510-834-0420 www.baylocalize.org October 31, 2007 D E S I G N , C O M M U N I T Y & E N V I R O N M E N T
    • TABLE OF CONTENTS1. EXECUTIVE SUMMARY/INTRODUCTION ........................................................ 1-12. EXISTING CONDITIONS .............................................................................. 2-13. ROOFTOP RESOURCE PROTOTYPES ............................................................. 3-14. FINDINGS .................................................................................................. 4-1AppendicesAppendix A: Assumptions and Methodology i
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TT A B L E O F C O N T E N T SList of FiguresFigure 2-1. Aerial view of buildings in study area with existing rooftop resources....................................................................... 2-4Figure 2-2. Aerial view of study area indicating distribution of building types. ......................................................................... 2-14Figure 3-1. Cross-section of Extensive Green Roof Prototype. .................. 3-3Figure 3-2. Cross-section of Intensive Green Roof—Vegetables prototype................................................................................... 3-9Figure 3-3. Cross-section of intensive Green Roof—Herbs prototype................................................................................. 3-14Figure 3-4. Cross-section of Rooftop Hydroponic Garden prototype................................................................................. 3-18Figure 3-5. Diagram of assembly of rainwater catchment system using 50-gallon drum. .................................................. 3-24Figure 3-6. Diagram of integrated Rainwater Harvesting and Solar Photovoltaics prototypes. .............................................. 3-25Figure 4-1. Aerial view of study area with buildings assigned rooftop resources prototypes. ................................................... 4-3List of TablesTable 2-1 Building Typology-Typical Characteristics ............................ 2-12Table 2-2 Building Type Distribution..................................................... 2-13Table 3-1 Prototype Characteristics.......................................................... 3-2Table 4-1 Prototype Assignment and Productivity ................................ 4-10ii
    • 1 EXECUTIVE SUMMARY/INTRODUCTION “Built-out” is a phrase often used in planning and development fields to de- scribe dense, urban communities that have few remaining vacant buildable parcels. As the Bay Area adopts smart growth and transit-oriented develop- ment policies emphasizing high-density housing, neighborhoods throughout San Francisco, the East Bay, Peninsula, and South Bay are becoming increas- ingly built-out. This density presents a challenge in identifying available land for important uses such as open space, community gardens, and stormwater and energy infrastructure. In cities across the country, however, a new land- scape is being discovered where building rooftops meet the sky. Previously regarded as unusable space, the landscape of rooftops is being re- claimed for productive and sustainable purposes. Whereas in the past, roofs have been a liability—emitting heat into the urban atmosphere, shedding pol- lutants into the watershed, requiring costly repair and replacement—some cities are transforming roofs into assets. They are being used as catchment areas for irrigation water, renewable energy platforms, recreational open space, food and educational gardens, reduction of stormwater surges, and aes- thetic improvement. In short, rooftops are being harnessed to improve cities and enhance the quality of life of inhabitants. A rooftop resource development philosophy is emerging and taking root in the Bay Area. Building owners and developers are looking at the options of solar power, rainwater catchment and living roofs to maximize their build- ings’ efficiency and function. Designers and planners are coming together to map out strategies for green roof implementation. Public works departments and utilities are stimulating adoption of solar photovoltaic systems. And citi- Rooftop garden atop St. Simon Stock Catholic School Bronx, New York. zens are seeking ways to better utilize rooftops for energy, food and commu- Source: St. Simon Stock Catholic nity empowerment. School. I. PROJECT OBJECTIVES Information on green roofs, solar technologies, and rainwater harvesting is available in abundance. This study seeks to fill gaps in that knowledge, par- 1-1
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X E C U T I V E S U M M A R Y / I N T R O D U C T I O Nticularly with regard to low-cost strategies on existing buildings and the po-tential productivity for future developments. The study analyzes rooftopresource implementation and benefits for the Eastlake district in Oakland.Objectives include: ♦ Analysis of the suitability of rooftop resource strategies in different built contexts, highlighting retrofits to existing buildings without structural improvement; ♦ Design of conceptual rooftop resource prototypes that are feasible for ex- isting buildings; ♦ Analysis of productivity for edible garden designs on future development in the area; and ♦ Quantification of the productivity benefits of rooftop gardens, renewable energy, and rainwater catchment technologies.Several unique contributions are addressed in this study, including: ♦ Focus on Existing Buildings. Most informational resources for green roof development focus on new construction; therefore, less information is available for building owners and policymakers to use when consider- ing the potential for green roof retrofits on existing buildings. ♦ Regional Context. Much of the available information on green roofs was developed in different social, political, economic, environmental and meteorological contexts, from Chicago to Germany to Portland to Mont- real. Also, while rooftop resource development in cities across the US and the globe is supported with public financial incentives, the Bay Area and the state of California fall short in implementing many of these poli- cies. ♦ Urban Agriculture. This study also differs from many existing docu- ments in that an emphasis is placed on rooftop vegetable gardening as a strategy for intensifying urban agriculture activities, which can improve nutrition and food security in urban neighborhoods while reducing de- pendence on an energy-intensive global food economy.1-2
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X E C U T I V E S U M M A R Y / I N T R O D U C T I O N ♦ Neighborhood Scale. This study looks beyond the analysis of green roof benefits at the building scale to focus primarily on projecting out- comes at the neighborhood scale.II. PROJECT APPROACHAs detailed in later chapters, this assessment analyzes the potential for greenroofs, rooftop gardens, solar photovoltaics, and rainwater harvesting on exist-ing buildings and future developments, and identifies possible benefits to theEastlake neighborhood in Oakland. A model was developed for this study toproduce quantitative estimates of rooftop productivity.Buildings in the Study Area were categorized into types to generalize theircharacteristics, including the weight-bearing capacity of the roof structure.Rooftop resource prototypes were then designed to serve as test retrofits,providing data on loading characteristics. The prototypes were tailored tomeet the special needs of existing buildings and were correlated with produc-tivity estimates per square foot. Prototypes were then assigned to each build-ing based on their suitability. Vacant lots were categorized as “opportunitysites” that could hold intensive, edible roof gardens. Finally, the total areaand productivity estimates of each prototype were used to determine aggre-gate benefits to the Eastlake Study Area.III. PROJECT FINDINGSThe findings of the assessment demonstrate a great deal of potential for har-vesting food, energy, and water on Bay Area roofs. Rooftop gardens, solarphotovoltaic systems, and rainwater harvesting technologies can all be fittedon existing buildings. There are clear opportunities and constraints to eachstrategy as well as some surprising benefits. In addition to well-documentedbenefits such as water quality and energy efficiency improvements, provision 1-3
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X E C U T I V E S U M M A R Y / I N T R O D U C T I O Nof open space amenities, and aesthetic appeal, rooftop resources in the StudyArea can provide: ♦ Clean, renewable electricity satisfying approximately 25 percent of de- mand; ♦ Fresh, leafy-green vegetables for all area residents; and ♦ Supplemental rainwater for irrigation for approximately 83 percent of the area’s buildingsThese benefits are attainable, but not without significant effort invested byState and local government, the private sector, communities and individualhouseholds.IV. REPORT STRUCTUREThe report is organized into four chapters: Introduction, Documentation ofExisting Conditions, Description of the Rooftop Resource Prototypes, andStudy Findings. Methodological approaches and assumptions are described inthe text or footnoted, and also described in greater depth in Appendix A.Figures are distributed throughout the text to provide accessible graphic illus-tration of concepts.V. ACKNOWLEDGEMENTSPreparation of this study was aided by several professional advisors andcommunity volunteers. Deserving of special acknowledgement are: ♦ American Soil and Stone ♦ Andrea Solk, Sustaining Ourselves Locally ♦ Association of Bay Area Governments ♦ Babak Tondre ♦ Center For Sustainable Economy1-4
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X E C U T I V E S U M M A R Y / I N T R O D U C T I O N ♦ City Slicker Farms ♦ Community Foundation Silicon Valley ♦ Institute for Simplified Hydroponics ♦ Intertribal Friendship House ♦ Laurence Levine Charitable Trust ♦ Mark Richmond, Practica Consulting ♦ Natylie Baldwin ♦ Rana Creek ♦ REC Solar ♦ San Francisco Planning and Urban Research Association (SPUR) ♦ Stewart Winchester, Merritt College ♦ Tufani Mayfield ♦ United Nations Food and Agriculture OrganizationBuilding Survey VolunteersAaron LehmerAndrea MannBob StrayerCarolyn BushCharles HardyDavid JaberDebbie CollinsDominic PorrinoEllen DoudnaInga SheffieldKelley LakeKirsten SchwindLisa KatzMaija DzenisMark McBethNelson ChickOliver LearPaula White 1-5
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X E C U T I V E S U M M A R Y / I N T R O D U C T I O NSarah KennedySharon KutzVI. CONCLUSIONThis Neighborhood Assessment conclusively demonstrates that rooftop re-sources can be developed on existing buildings in the Bay Area without struc-tural improvements. Furthermore, future developments would gain consid-erable benefits by planning for intensive, edible roof gardens. Hydroponicrooftop gardens and solar photovoltaics show the most promise for existingbuildings, while intensive and extensive green roofs and rainwater harvestingpresent additional challenges, some of which may be overcome in time ifgreater investment is warranted. Today, it is possible for building owners toinstall rooftop technologies and improve water quality, save energy, growfresh produce, generate clean electricity, and contribute to greater communityresilience and livability. The promise of a healthier environment and greaterresource security makes it imperative that we begin planning and implement-ing for these sustainable rooftop systems now.Education and leadership can bring about the kinds of benefits that so manycities have successfully demonstrated. Policy and government support areessential keys to fostering the implementation of these systems. Rooftops arecurrently untapped resources and a package of appropriate design, develop-ment incentives, and public support is crucial to fulfilling their great poten-tial.1-6
    • 2 EXISTING CONDITIONS This chapter describes the current state of rooftop resource implementation in the Bay Area and specifically in the Study Area. It also documents the ar- chitectural history and existing demographic and regulatory setting of the Eastlake neighborhood in order to identify dynamics that may affect rooftop resource development. The latter half of the chapter presents the Building Typologies that were developed for the purposes of the assessment and de- scribes their distribution in the Study Area. I. ROOFTOP UTILIZATION The role of rooftops has historically been a peripheral consideration in the development of urban infrastructure and largely remains an afterthought in water, food and energy systems planning. Roofs have been used for collecting water or insulating homes for millennia, but widely-held perceptions dismiss these traditionally “low-tech” strategies as being old-fashioned or only appli- cable in rural contexts. While solar thermal and photovoltaic technologies have been applied on roofs for decades, these practices have yet to gain wide- spread adoption. However, new interest in green building is once again fo- cusing attention on rooftops. Green roofs, rainwater harvesting systems, and rooftop photovoltaics are being installed at an increasing rate while California Buildings within study area. Source: Ingrid remains a national leader in solar electricity generation. Severson. A. Rooftop Utilization in the Bay Area The Bay Area is well-known for its focus on environmental sustainability and for good reason. With regards to rooftop resource strategies, the region is ahead of the curve but far from taking full advantage of its resources. 2-1
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X I S T I N G C O N D I T I O N S1. Solar Photovoltaic InstallationsIn the nine-county Bay Area, over 5,000 photovoltaic systems have been in-stalled.1 The largest include the 675 kilowatt (kW) installation on the City ofSan Francisco’s Moscone Center, a 766 kW system at the Rodney StrongWinery in Healdsburg, and Alameda County’s 1,180 kW installation on theSanta Rita Jail in Dublin. In addition, much of the region’s photovoltaic ca-pacity exists in smaller systems under 15 kW, many of which serve residentialbuildings. In seven counties of the Bay Area (excluding Napa and SolanoCounties), these systems comprise approximately 18,000 kW, or 18 mega-watts (mW) of electricity generating capacity.22. Green Roofs and Rooftop GardensDespite a number of high-profile green roof projects in the Bay Area, thegreen roof trend has been somewhat slow to take hold in the region. An out-standing exception is the Gap Headquarters in San Bruno, which was con-structed with a 69,000 square-foot extensive green roof in 1997. The Califor-nia Academy of Sciences building under construction in San Francisco’sGolden Gate Park will also have a large, extensive green roof. Intensive greenroofs and rooftop gardens and parks have also been built, including park en-vironments atop parking garages at Civic Center, Yerba Buena Gardens andthe North Beach Place mixed-use project in San Francisco, and at the KaiserCenter office complex in downtown Oakland.Nevertheless, a number of cities have consistently outperformed Bay Arealocations in terms of green roof implementation, including Chicago, Wash-ington D.C., New York City and Portland, Oregon.3 As far as could be de-1 Liz Merry, “Status of Photovoltaic Installations in California,” Solar Energy ResourceGuide, NorCal Solar, 2007.2 Ibid.3 Green Roofs for Healthy Cities, “Green Roof Industry Survey Final Report,”http://www.greenroofs.org/storage/2006grhcsurveyresults.pdf (accessed April 14,2007).2-2
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N Stermined, no municipalities in the Bay Area region have green roof incentiveprograms as do Chicago and Washington, D.C.3. Rainwater HarvestingRegional attention to harvesting rainwater has fluctuated with concerns overenvironmental conditions or scarcity. Many residents discovered rainwaterharvesting, for example, in the drought of 1976-77, when reservoirs across theregion were dangerously drawn down and mandatory restrictions were im-posed on water use. While data on regional rainwater catchment implemen-tation is unavailable, it is likely that a limited number of residential buildingsare fitted with rainwater harvesting systems, and that this number is increas-ing, albeit very slowly, with elevated awareness of California’s water resourceand sustainability challenges.B. Rooftop Utilization in the Study AreaA limited level of rooftop utilization is already occurring in the Study Area.There are at least six rooftop solar water heating installations, all on apart-ment buildings. There are no green roofs on occupied buildings in the area,but a vegetated plaza sits atop an underground parking structure. The plaza is Volunteers identifying building types. Source:planted with a variety of trees, grasses, and shrubs, providing an attractive DC&E.semi-public space with stormwater retention benefits. It is possible that somerainwater harvesting systems are in use but none were identified through ae-rial photograph analysis or the field survey. Figure 2-1 illustrates existingrooftop resources in the area.II. REGULATORY AND POLICY SETTINGThe Study Area is within the jurisdictional boundary of the City of Oaklandand is subject to a number of State and City regulations pertaining to rooftopuses. This section introduces these regulations and their applicability to thestudy. 2-3
    • BAY LOCALIZE ROOFTOP RESOURCES NEIGHBORHOOD ASSESSMENT E. 19th St. d. Blv rk Pa E. 18th St. St . 8 th E. 1 E. 17th St. Lake Merritt Foothill Blvd. . vd Bl e or sh ke La E. 15th St. 1st Ave. 2nd Ave. 3rd Ave. 4th Ave. 5th Ave. 6th Ave. 7th Ave. 8th Ave. International Blvd. Clinton Square Park E. 12th St. E. 11th St. E. 10th St. Intensive Green Roof No Resource 0 250 500 Feet Solar Water Heating Study AreaFigure 2-1. Aerial view of buildings in study area with existing rootop resources.
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N SA. Zoning CodeThe Zoning Code is contained in Title 17 of the City of Oakland’s MunicipalCode. The Code classifies, regulates, restricts and segregates land uses, build-ing characteristics, and population densities according to the land use goalsestablished by the community in the General Plan. Minimum requirementsfor usable open space are established for residential uses. In Chapter 17.126,the Code sets minimum standards for usable open space on residential parcels,including rooftop uses.Residential parts of the Study Area are mostly zoned R-50 (Medium DensityResidential) or R-60 (Medium-High Density Residential), with the remainder Mixed use building. Source: DC&E.zoned at higher densities. Usable open space requirements for these classifica-tions range from 150 to 200 square feet per dwelling unit. Rooftop areas cansatisfy a maximum of 20 percent of this required open space, or 30 to 40square feet per dwelling unit.B. California Building CodeThe State Building Code is contained in Title 24, Part 2 of the CaliforniaCode of Regulations. The Code regulates the construction and function ofbuildings to ensure fire and life safety and adequate structural design. Perti-nent sections of the code include Chapter 5, Section 509 (Guardrails), Chapter10 (Means of Egress), Chapter 13, Section 1301 (Solar Energy Collectors),Chapter 15 (Roofing and Roof Structures), and Chapter 16 (Structural DesignRequirements). The following considerations will affect the extent to whichusable rooftop spaces can be created.1. Occupancy Load and Means of EgressSince construction of an accessible space on a rooftop alters the use of theroof, the municipal Building Department will ensure that Building Code re-quirements are met when reviewing plans for the improvement. Code re-quirements will vary depending on how the occupancy of the roof space is 2-5
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X I S T I N G C O N D I T I O N Sdefined and on the maximum number of occupants expected and allowed touse the space, which is the “occupant load.”The most relevant example is with regard to means of egress.4 Accessible roofspaces that accommodate many occupants will be required to provide morethan one exit, while spaces intended for ten or fewer occupants are adequatelyserved by one exit. This is a critical variable for rooftop gardening since veryfew buildings have two exits from the roof. Therefore, for rooftop gardeningto be possible, the Building Department must ensure safety by either callingfor two exits or determining that the rooftop garden’s occupancy load will beten or less, rendering one exit sufficient.The Building Department is responsible for assigning an occupancy load tothe rooftop space, in accordance with the following direction from Chapter10, Section 1003 of the California Building Code: ♦ Areas with fixed seats. Occupant load for areas with fixed seats is de- termined by assigning one occupant per seat provided in the area. For example, an area with 12 seats has an occupant load of 12. ♦ Areas without fixed seats. Here the occupant load is determined by di- viding the occupied square footage by an “occupant load factor” in Table 10-A of the California Building Code. For uses not included in the table, such as gardening, a factor for a similar type of use will be used. Specula- tively, a case could be made that gardening is similar in intensity of use to such uses as manufacturing or a commercial kitchen, where a limited number of people are involved in a productive activity over a large area. If these factors are used, as much as 2,000 square feet can be occupied for gardening without exceeding the maximum desirable occupant load of 10.Because rooftop gardening is a relatively rare phenomenon in the region, nointerpretation of the Code with regards to occupancy has been established. It4 Means of egress are Code-compliant exits. Any occupiable space, such as a rooftopgarden, must have at least one Code-compliant means of egress.2-6
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N Sis possible that Code officials will be wary of rooftop uses more intensivethan gardening and will consider the space a gathering place, thereby requir-ing an additional exit. The outcome will depend on the municipality and onassurances that can be made to limit the number of occupants.2. GuardrailsChapter 5 of the Building Code requires a guardrail around habitable space inorder to protect life safety. Some buildings in the Study Area have fixed para-pets lining the perimeter of the roof area and extending as high as a few feet.Others have no perimeter barrier at all. In any case, a code-compliance bar-rier that extends 42 inches in height is required.C. AccessibilityLocal, State, and federal governments address accessibility for the mobility-impaired through several codes and laws. At the federal level, the Americanswith Disabilities Act (ADA) requires that equal access be provided for themobility-impaired when alterations to public spaces are made. Chapter 11 ofthe California Building Code also sets forth stipulations for accessibility,which are enforced by municipal Building Departments. Both the ADA andChapter 11 must be satisfied.1. Americans with Disabilities Act ComplianceADA requirements for building alterations do not apply to buildings that areused for strictly residential purposes; only buildings considered “public ac-commodations”—such as restaurants, hotels, theaters, doctors’ offices, phar-macies, retail stores, museums, libraries, parks, private schools, and day carecenters—are subject to ADA rules. Some rooftop garden retrofits that areaccessible to the public would fall under ADA and would need to includeaccessibility features to the roof, in the form of either elevators or ramps. It islikely that these features would prove prohibitively expensive to install andwould create a major disincentive for creating accessible rooftop spaces onexisting buildings. 2-7
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X I S T I N G C O N D I T I O N SADA requirements apply only to public accommodations and do not addressresidential environments. Even for public accommodations, elevators wouldnot be required in many cases. According to the Department of Justice, ele-vators are generally not required in facilities under three stories or with fewerthan 3,000 square feet per floor, unless the building is a shopping center ormall; the professional office of a health care provider; a terminal, depot, orother public transit station; or an airport passenger terminal.5 In addition,accessibility requirements may be waived as an undue hardship if accessibilityfeatures cost more than 20 percent of the total alteration cost, which wouldapply in the case of rooftop gardens.2. California Building Code, Chapter 11Accessibility requirements in the State Code are similar to ADA require-ments, but also include residential uses in their scope. Like the ADA, theCode allows for exemptions based on “unreasonable hardship,” which waivesaccessibility requirements when the cost of accessibility features exceeds 20percent of the total alteration cost, and the total alteration cost is less than$120,000 (both of which are true for rooftop gardens). Installation of a newelevator in an existing building in order to access a new garden on the roofmay be acknowledged as unreasonable hardship, particularly if the structureis not a major commercial or institutional building.Every effort should be made to provide universal accessibility to rooftop gar-dens when feasible. The Americans with Disabilities Act and CaliforniaBuilding Code require that these improvements be made whenever feasible,but may provide flexibility when the costs of accessibility improvements areunreasonably high, as with elevator installation in existing residential struc-tures and other small buildings.5 US Department of Justice, “Americans with Disabilities Act Questions and An-swers,” http://www.usdoj.gov/crt/ada/qandaeng.htm.2-8
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N SIII. STUDY AREA CHARACTERISTICSComprising roughly one-quarter of a square mile, the Study Area consists ofthe Eastlake commercial district and surrounding residential neighborhoodssoutheast of Lake Merritt in Oakland. The area provides a fertile testingground for rooftop resource feasibility due to its great diversity, both in itssocioeconomic conditions and its built environment.A. Demographics Mixed-use building on 2nd Avenue.Eastlake is a unique neighborhood demographically, presenting a complexmix of economic and ethnic attributes in a compact area. Extrapolation ofcensus data suggests that the Study Area is home to approximately 7,000 resi-dents in approximately 3,500 dwelling units. The median income of around$31,000 is low relative to the City of Oakland as a whole, but the number ofpeople below the poverty line is lower than the city average.6 A wide rangeof income levels exists in the area.The neighborhood is widely perceived as one of the most ethnically diverse inthe region. Dozens of languages are spoken by immigrants from around the Pitched-roof houses.world. Asians and African-Americans are the largest ethnic groups, compris-ing roughly one-quarter of the population each, with Hispanics accountingfor another 14 percent and the remainder White, or other races. Of residentswith Asian ancestry, many trace their roots back to Vietnam and otherSoutheast Asian countries. Parking garage in study area. Source: Ingrid Severson.6 Estimates based on U.S. Census Bureau, U.S. Census 2000. 2-9
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N S B. Architectural History Known variously over the years as Rancho San Antonio, Clinton, Brooklyn, and New Chinatown, Eastlake is a neighborhood with a complex and fasci- nating history that is reflected in the building stock found there today. While the built remnants of the Ohlone communities that originally occupied this area have disappeared, historic features dating back to Spanish settlement can still be found. San Antonio Park, lying just southeast of the study area, once served as the main plaza of Rancho San Antonio, the cattle ranch started by the East Bay’s original Spanish settlers in the 1820s. Apartment tower. The area was incorporated into Oakland in 1872. At least one 19th century home still stands in the neighborhood, along with several early 20th century Victorian homes. Many multi-family residential and commercial buildings found in the area today were constructed in the early 20th century, leading up to World War II. After the War, Eastlake experienced the same pattern of disinvestment that impacted many urban neighborhoods across the country. Deteriorating buildings continue to impact quality of life in Eastlake today and many structures in the study area are in fair or poor condition. Mid- century urban renewal projects also had an effect with hundreds of structures demolished in these decades and replaced with apartment buildings—1,108 “Shops” building type. apartments in 57 buildings total.7 Many of these renewal-era buildings are still found in the study area and factor significantly into the rooftop resource assessment. Since the era of urban renewal, the built conditions of the study area have not changed as rapidly. Investment in the 1980s and 1990s was primarily directed to areas near Lake Merritt where apartment towers, strip retail and big-box retail were developed. However, it appears that Eastlake may be in the early stages of economic transition. The neighborhood is located in the City of Oakland’s Central City East Redevelopment Area, in which infrastructure for development projects may be financed through tax-increment financing,Repair shop. Source: Ingrid Severson. 7 Urban Ecology, Clinton Park Plan, August 1999. 2-10
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N Sproviding a public incentive for private development. A multi-million dollarstreetscape improvement project was also initiated in 2002 for the businessdistrict on 12th Street and International Boulevard between 5th Avenue and 8thAvenue. Rehabilitation and new construction projects in Eastlake may pro-vide an opportunity to incorporate rooftop features into the neighborhood.IV. BUILDING TYPOLOGYBuildings in the Study Area are classified by type for the purposes of this as- “Big Box building. Source: Ingrid Severson.sessment. The typology categorizes flat-roofed buildings into eleven types toallow for generalized estimates of structural properties and roof loading ca-pacities. Buildings with pitched roofs are not included in the typology sincethey were assigned the rainwater harvesting and solar photovoltaic proto-types. Both systems are sufficiently lightweight to be installed on virtually allpitched roof buildings, regardless of the building type. To account for thepotential of future development in the area, vacant lots were identified as op-portunity sites in which new construction could plan for the inclusion ofrooftop systems. Table 2-1 describes the typical characteristics of each flat-roofed building type and associated roof loading capacities. Typical office building. Source: DC&E.In addition to assigning a building type to each flat-roofed structure, a fieldsurvey conducted by the consultants and Bay Localize volunteers recordeddiscrete characteristics such as occupancy type, height, construction type andera, and presence of a “soft story.” Estimates of loading capacity are refinedto account for differences in these factors when they do not match the typicalassumed characteristics of the building type.A. Building Type Distribution One of nine vacant lots identified as opportu-A wide variety of building types are found in the Study Area. Table 2-1 de- nity sites. Source: Ingrid Severson.scribes the building type split over the area. Table 2-2 illustrates the distribu-tion of building types in the area. 2-11
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TE X I S T I N G C O N D I T I O N STABLE 2-1 BUILDING TYPOLOGY-TYPICAL CHARACTERISTICS Additional Loading Occupied Construction Capacity*Building Type Land Use Stories Construction Material Era Size/Scale (psf)House Residential 1-2 Wood-framed Any Up to 4 units 20Apartment Building Residential 1-4 Wood-framed After 1950 4 to 10 units 15Apartment Tower Residential 5+ Concrete or Steel After 1980 More than 10 units 5-7 Retail/ VariesMixed Use 2-5 Wood framed Any Varies Residential (8-12)Shops Commercial 1 Wood-framed After 1970 Varies 17 Masonry or Concrete blockWarehouse Varies 1 walls, riveted steel or large- Prior to 1960 Large, open floor plan 5 timber columns Retail, Concrete block or tilt-up con-Big-Box 1 After 1960 Large, open floor plan 5 Industrial crete walls, interior steel posts Smaller, open floorRepair shop Commercial 1 Concrete block Any 7 plan, open storefrontOffice Building Office 2+ Varies After 1960 Varies 17 School, hospital, church, auditorium, library, thea- VariesCommunity Building 1+ Varies Varies Varies ter, police, fire, post office, (5-17) etc.* A removal of pea-gravel/rock ballast (secured on the roofs of any of these buildings) can increase the “dead-load” capacity by an average of 4-5 psf for every inch of ballast removed. 2-12
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T E X I S T I N G C O N D I T I O N STABLE 2-2 BUILDING TYPE DISTRIBUTION Number PercentageBuilding Type of Buildings of TotalHouse 20 2.7Apartment Building 160 21.3Apartment Tower 8 1.1 Community building. Source: Ingrid Severson.Mixed Use 36 4.8Shops 40 5.3Warehouse 14 1.9Big Box 7 0.9Repair Shop 6 0.9Office Building 7 0.9Community Building 30 4.0 Apartment building. Source: DC&E.Parking Garage 1 0.1Pitched Roof Building 419 56.01Total 748 99.91 Warehouse building. Source: Ingrid Severson. 2-13
    • BAY LOCALIZE ROOFTOP RESOURCES NEIGHBORHOOD ASSESSMENT E. 19th St. d. Blv rk Pa E. 18th St. E. 17th St. Lake Merritt Foothill Blvd. . Bl vd re E. 15th St. sh o 1st Ave. 2nd Ave. 3rd Ave. 4th Ave. e 5th Ave. 6th Ave. 7th Ave.Lak 8th Ave. International Blvd. Clinton Square Park E. 12th St. E. 11th St. E. 10th St. 0 250 500 Feet Figure 2-2. Aerial view of Study area House Big Box Repair Shop indicating distribution of Apartment Building Shops Opportunity Site building types. Apartment Tower Office Building Unknown Mixed Use Parking Garage Pitched Roof Community Center Warehouse Study Area
    • 3 ROOFTOP RESOURCE PROTOTYPES For the purposes of this assessment, five rooftop resource prototypes were developed. These prototypes provide assumed characteristics that can be ap- plied to each of the rooftop resource models, including weight and productiv- ity. This chapter describes the design concepts, architectural and maintenance requirements, and potential benefits of the five prototypes. It also analyzes the synergies and conflicts that could arise if the prototypes are implemented in concert. The rooftop resource prototypes are a set of design concepts that represent various strategies for rooftop utilization. The design process was informed by Raised vegetable garden on rooftop. Source: the objective of utilizing rooftops in a manner that is productive, sustainable, Resource Centres on Urban Agriculture and and feasible. In addition, the goal of assessing rooftop capacity on existing Food Security. buildings in their current condition—rather than on new construction or on structurally reinforced buildings—made loading a central consideration in the prototype design. Table 3-1, found at the end of the chapter, describes the components, cost ranges, and yields of the prototypes. The prototypes are necessarily generalized to allow for variations in roof size and type, roof slope, building type, wind variables, client budget, and other conditions. They should be taken as examples of possible configurations and should not be relied upon for specifications for any site. Before any specific rooftop resource is developed, professional consultation should be obtained to determine precise design loads and roof loading capacity. I. EXTENSIVE GREEN ROOF A. Design Concept Extensive green roofs are the most common type of green roof found today, valued for their many environmental benefits. The prototype follows the typical configuration of extensive green roofs in arid climates, in which low- growing, drought-tolerant ground cover is planted in 4 to 6 inches of growing substrate and placed on an assembly of filter fabric, a drainage layer, root 3-1
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S TABLE 3-1 PROTOTYPE CHARACTERISTICS Annual Major Maximum Productive Prototype Components Weight Yield ½" Drainage Mat Extensive Green drainage and 4" Mineral Substrate 22 psf Roof energy benefits Sedums 2¼" Drainage Board Intensive Green 1.86 psf 18" Organic/Mineral Substrate 108 psf Roof—Vegetables vegetables Variety of Vegetable Crops 1 ¼" Drainage BoardExtensive green roof. Source: American Intensive Green 8" Organic/Mineral Substrate 51 psf perennial yieldHydrotech. Roof—Herbs Herbaceous Plants Growing Container Hydroponic Reservoir Container 4 psf 16 psf Rooftop Garden 4" Inert Substrate vegetables Variety of Vegetable Crops Solar Multicrystalline PV Panels 1 kilowatt per 5 psf Photovoltaics Mounting Hardware 100 square feet Conveyance-Gutters/Leaders average Debris Screen 3,000 ga. per Rainwater First-flush Diverter N/A structure Harvesting Roof Washer (1" rain on 100 sf Storage Tank/Cistern = 60 gal.) barrier, and a waterproof roof membrane. This type of assembly can be in- stalled directly on the roof or placed in trays that are installed as a modular system. Extensive green roofs differ from intensive green roofs in the mini- Extensive green roof assembly. Source: mal depth of the substrate and more limited planting possibilities. Figure 3-1 American Hydrotech. illustrates the prototype assembly and vegetation. 1. Green Roof Assembly The Extensive Green Roof prototype is intended to extend across the maxi- mum feasible area of the building to confer the greatest storm water and en- ergy benefits. Plants are established in four inches of substrate, considered a minimum depth for plants to endure dry Bay Area summers. In this case a 3-2
    • B AY L O C A L I Z E R o o f t o p R e s o u r c e s N e i g h b o r h o o d A s s e s s m e n tFigure 3-1. Cross-section of Extensive Green Roof prototype.
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S blend with high mineral content and low organic content should be devel- oped to provide moisture and air retention while minimizing the load im- posed upon the roof. While the exact blend depends highly on the site, one very appropriate medium is pumice, which is one of the lightest mineral ma- terials mined within 500 miles of the Bay Area. Expanded shale is another very lightweight mineral that exists in California; however, it is currently shipped in from Colorado and other Western states, resulting in higher trans- portation costs and environmental impacts. Lava and scoria are available from the Clearlake area in Northern California, but they are heavier than pumice and expanded shale. Whichever mineral medium is selected should beExtensive green roof modular tray system.Source: Green Roof Blocks. combined with a minimal amount of organic material, such as locally- available compost. Beneath the substrate, a ½-inch thick recycled polyethylene drainage mat aer- ates and drains the media, and attached filter fabric prevents it from clogging the drainage layer. Finally, a root barrier and waterproof membrane protect the roof deck from the living layer above. A popular alternative to the type of assembly described above (which is built- up directly on the roof) is the modular approach, in which the above compo- nents are assembled in container trays and installed on the roof. Modular systems present a number of benefits. Perhaps their most notable benefit is“Green Paks” modular tray system. Source: the flexibility they allow in installation and removal. They can often be in-Green Roof Blocks. stalled without re-roofing, while the soil membrane system may require re- placement or major repair to the roof membrane. In addition, building own- ers may be more open to experimenting with a green roof installation know- ing that the trays can be easily removed if desired. Whether the soil membrane approach or the modular system is chosen for a particular roof, the described components of the extensive green roof assem- bly are almost identical in other respects. 3-4
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S2. PlantsThe Extensive Green Roof prototype is planted with of a mix of regionally-appropriate sedums, such as Sedum album, Sedum spathuifolium, Sedum spu-rium, and Sedum sexangulare. The specific species chosen for a particularrooftop context depends on many factors, including: ♦ Initial budget and maintenance budget. ♦ Physical conditions, such as shading and wind. ♦ Roof slope. ♦ Retrofit schedule and seasonal variables.Planting methods can vary, from direct seeding in the growing medium dur-ing installation to application of pre-planted container trays or vegetatedmats. Generally, materials for vegetated mats and modular tray systems aremore expensive but labor costs are reduced, while seeding or transplantingplugs directly is more labor-intensive but reduces materials costs.B. Architectural RequirementsBecause extensive green roofs are a low-impact, low-maintenance rooftop re- Sedums on extensive green roofs using modularsource, they can be useful on buildings with a wide range of characteristics. systems. Source: Green Roof Blocks.Their implementation on existing buildings in the Bay Area is constrained,however, by their weight. The lightweight Extensive Green Roof prototypeweighs approximately 22 pounds/square foot (psf),1 precluding installation onmany building types. This weight value is at the low end of the spectrum forextensive green roofs.Because the prototype is not intended to be used as occupiable space, egressrequirements are more lenient than for rooftop gardens. Older stairways1 All green roof loading estimates are based on design loads from the German greenroof standard, “Guidelines for the Planning, Execution, and Upkeep of Green-roofSites,” published by FLL (Forschungsgesellschaft Landschaftsentwicklung Land-schaftsbau e.V.), 2002 Edition. 3-5
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TR O O F T O P R E S O U R C E P R O T O T Y P E Swith steeper inclines to the roof, or common ladder and hatch access, wouldboth be sufficient to provide necessary maintenance.C. Maintenance RequirementsExtensive green roofs are intended to be a low-maintenance technology. Dur-ing the first year after installation, plants need to be irrigated as they establishthemselves. Planting hardy, drought-resistant, regionally-appropriate varie-ties such as those specified in this prototype will limit irrigation needs overthe long-term since these plants are accustomed to the arid conditions of BayArea summers. However, minimizing substrate depths to the level entailed inthis prototype would likely require that some irrigation occur on a regularbasis, depending on the conditions of the site. The extensive green roof needsto be inspected only a few times a year to ensure that all components, includ-ing the membrane, are functioning as intended.Extensive green roofs can reduce roof maintenance demands and as much asdouble the life of the roof membrane by protecting it from extreme tempera-ture changes, ultraviolet radiation, and accidental damage.2D. Cost RangeThe extensive green roof prototype is a relatively low-cost rooftop resourcestrategy, though initial costs are higher than that of a conventional roof. De-pending on the type of labor that is used, accessibility and size of the roof,and the planting method, initial materials and labor costs are estimated at $152 City of Chicago, Design Guidelines for Green Roofs,http://egov.cityofchicago.org/webportal/COCWebPortal/COC_ATTACH/design_guidelines_for_green_roofs.pdf (accessed April 8, 2007).3-6
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E Sto $22 per square foot. This estimate assumes that the prototype is appliedwhen a new roof is needed and therefore excludes the cost of a new roofmembrane, which generally adds another $8 to $12 per square foot. Pre-planted trays with irrigation in place cost approximately $25 to $30.3In considering the financial viability of extensive green roofs, it is importantto note that they are more cost-competitive with conventional roofs whenusing a life-cycle costing approach, which incorporates savings from reducedmaintenance and longer roof life, as well as ongoing energy efficiency savings.Life-cycle costing is a valuable method for understanding the benefits of many“green” technologies, which may cost more initially but which may result incost savings over the operating life of the product.E. BenefitsWhile the extensive green roof prototype does not yield a harvest of food,energy, or water, it does confer a number of environmental and aestheticbenefits, including: ♦ Storm Water Retention. Extensive green roofs are valued for their storm water retention capacity and a good deal of research is being con- ducted to quantify these benefits. By capturing and holding water in the vegetation and substrate layers, the extensive prototype can mitigate flooding and combined sewer system backup (where applicable) in heavy rain events. This prototype can also improve the quality of runoff water by capturing and holding pollutants in the substrate. Studies indicate that an extensive green roof can absorb as much as 70 percent of rainfall3 All costs are derived from Steven Peck and Monica Kuhn, “Design Guidelines forGreen Roofs,” Ontario Association of Architects and Gabrielle Fladd, “Green RoofMatrix” (cost analysis paper presented in San Francisco Planning & Urban ResearchAssociation, Green Roof Task Force meeting, San Francisco, CA, June 2007). 3-7
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S from a storm event, releasing the remainder over an extended period of time.4 ♦ Energy Efficiency. The extensive prototype can improve building per- formance, effectively acting as a heat trap, while also shading the roof and cooling the roof surface through evaporation and vegetative transpira- tion. A study in Canada found that when implemented broadly on a city or regional scale, extensive green roofs can significantly reduce ambient urban temperatures, thereby lowering energy demand for air condition- ing. The living roof on Chicago’s city hall building stands as a popular case study modeling the cooling effect of green roofs. It has been re-Intensive roof garden. Source: AmericanHydrotech. corded as 7 degrees cooler than surrounding roofs on an annual average, and up to 30 degrees cooler during the summer time.5 II. INTENSIVE GREEN ROOF-VEGETABLE GARDEN A. Design Concept The Intensive Green Roof—Vegetable Garden prototype is designed to sup- plement the environmental and aesthetic benefits of the extensive prototype with food production and an open space amenity. Vegetables would beIntensive green roof—vegetable garden. grown in 18 inches of growing medium, the minimum depth to support aSource: The Rooftop Garden Project,Alternatives, 2004. large variety of vegetables. The assembly of the prototype is similar to that of the extensive prototype, consisting of a water proof membrane, root barrier, drainage layer, filter fabric, substrate layer, and plants. Figure 3-2 provides a section of the green roof assembly. 4 ASLA et al., “Landscape Architects Release Green Roof Performance Report: Roof Retained 27,000 Gallons of Stormwater in First Year,” http://asla.org/press/2007/ release091907.html. 5 Karen Liu, “A National Research Council Canada Study Evaluates Green Roof Sys- tems’ Thermal Performances,” http://www.professionalroofing.net/article.aspx? A_ID=130 (accessed April 8, 2007). 3-8
    • B AY L O C A L I Z E R o o f t o p R e s o u r c e s N e i g h b o r h o o d A s s e s s m e n tF i g u r e 3 - 2 . C r o s s - s e c t i o n o f I n t e n s i v e G r e e n R o o f — Ve g e t a b l e s p r o t o t y p e .
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S In this case, however, the vegetated roof is not intended to cover the entire roof area. Instead, paths are created by closing in growing areas with retain- ing walls, constructed of lightweight materials such as wood or recycled plas- tic. A protective surface would be installed to protect the roof from foot traf- fic damage. This arrangement provides accessible spaces similar to ground- level container gardens. While a multitude of different arrangements are pos- sible, depending on the existence of fixed obstructions on the roof, it is esti- mated that this prototype would provide an average growing area of 60 per- cent of total roof area. This estimate takes into account space unavailable due to fixed obstructions as well as space needed for paths and equipment storage.Crop Variations 1. Green Roof AssemblyA wide variety of vegetables may The prototype includes 18 inches of substrate, in this case a blend of aboutbe suitable for rooftop environ- equal parts mineral and organic content. Conventional topsoil and pottingments in the East Bay, despite soil are inappropriate media for rooftop environments, particularly on exist-such challenges as wind, heat, and ing buildings, due to their weight. Instead, the medium used in this proto-evaporation. Experimentation is type would include approximately equal parts organic material, such as com-needed to better establish planting post or bark humus, and mineral material such as pumice or scoria. Thepossibilities. While the prototype drainage layer in this prototype is a 2¼ inch thick recycled polystyrene drain-suggests several popular garden age board. The drainage course is filled with lava or similar mineral materialvegetables, other appropriate for structure. Other components are similar to the extensive green roof pro-edible crops may also include totype.broccoli, celery, chard, collards,eggplant, kale, mustard, green 2. Plantsonions, and peppers. In addition, The prototype is designed to provide year-round vegetables that could thrivesome of these crops may be in the Bay Area. A selection of vegetables was developed based on severalplanted in less than 18 inches of criteria, including:growing media, which was used ♦ Regional suitabilityin this prototype as a conservative ♦ Growing medium depth requirementsvalue for growing a large varietyof edible plants in potentially ♦ Plant weight at maturity (structural consideration)harsh conditions. ♦ Height at maturity (wind loading considerations) ♦ Full sun tolerance ♦ Normal to low water needs ♦ Growing season 3-10
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E SBased on these criteria, plants were selected that could be rotated to grow ona year-round basis. Cool-season crops in the prototype are spinach, mustard,carrots, and beets. Tomatoes, cucumbers, and winter squash are included aswarm-season crops, along with leaf lettuce, which in many cases can be grownyear round. Variations on this arrangement should provide an opportunityto grow cool-season crops twice yearly—planted in the early Spring and Fall—while planting warm-season crops in late Spring. Additional crops that couldbe grown on this prototype are listed in the side box.B. Architectural RequirementsThe vegetable garden prototype would introduce a new roof load of ap-proximately 108 psf to the structure.6 Providing this type of structural sup- Intensive green roof assembly. Source:port would require a uniquely-tailored structural design incorporated into American Hydrotech.new construction. As an occupiable space, the vegetable garden prototypewould require a code-compliant stairway or elevator, as well as guardrails orfencing around the roof edge.C. Maintenance RequirementsThe prototype would require substantial maintenance, much of which is as-sociated with normal vegetable gardening activities. Maintenance demandswould include regular irrigation, pruning, weeding, fertilizing, and pest con-trol. Water needs could be increased relative to ground-level gardening due tohigher rates of heat- and wind-induced evaporation. Depending on budget,irrigation could take place through hand-watering or sub-surface drip irriga-tion, the latter of which would reduce water use and labor requirements. In6 All green roof loading estimates are based on material design loads in the Germangreen roof standard, “Guidelines for the Planning, Execution, and Upkeep of Green-roof Sites,” published by FLL (Forschungsgesellschaft Landschaftsentwicklung Land-schaftsbau e.V.), 2002 edition. 3-11
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TR O O F T O P R E S O U R C E P R O T O T Y P E Saddition to regular maintenance of the growing area, inspection and repair ofthe roof membrane would be required on an occasional basis.D. Cost RangeInitial costs depend greatly on the type of labor that is used, accessibility ofthe roof, and planting method, as well as the size of the roof. Given thesevariables, it is estimated that materials and labor costs to install this prototypewould range from $30 to $45 per square foot of growing area, plus an addi-tional $20 to $40 per linear foot for guardrails and an optional $2 to $4 persquare foot if irrigation is installed.7 This estimate assumes that the prototypeis applied when re-roofing is needed and therefore excludes the cost of a newroof membrane. It also assumes that structural and architectural require-ments of the Building Code are already satisfied.E. BenefitsIn addition to providing storm water retention and treatment, energy effi-ciency and aesthetic benefits, this prototype provides an open-space amenityto building residents. Food production on the roof also results in a numberof valuable outcomes, such as new wildlife habitat, recreational and educa-tional opportunities, and readily accessible fresh, healthy produce. Ade-quately maintained year-round, this prototype would yield approximately1.86 pounds of vegetables per square foot annually.87 Stephen Peck and Monica Kuhn, “Design Guidelines for Green Roofs,”http://egov.cityofchicago.org/webportal/COCWebPortal/COC_ATTACH/design_guidelines_for_green_roofs.pdf (accessed March 24, 2007).8 Nancy Garrison, “Home Vegetable Gardening,” University of California Coopera-tive Extension, http://vric.ucdavis.edu/veginfo/veginfor.htm. This figure is an aver-age of vegetables’ approximate yields, multiplied by three seasons.3-12
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E SImplemented on a broader scale, this type of green roof can improve localfood security and reduce “food miles traveled,” thereby reducing the energyand climate impacts of food transportation. A study conducted in 2001 atIowa State found that in the conventional American agriculture system, foodtravels an average of 1,500 miles from its origin to its point of consumption.9III. INTENSIVE GREEN ROOF—HERB GARDENA. Design ConceptThe concept of this prototype is largely similar to the Vegetable Garden pro-totype, except that herbs are grown instead of the wider variety of vegetables. Intensive roof garden atop the Fairmont RoyalPlants included are rosemary, thyme, and cilantro. The growing medium York Hotel in Toronto grows vegetables,remains the same—a lightweight, soil-free mix of approximately equal parts herbs, and edible flowers. Source: Lorraineorganic and mineral material—but substrate depth is reduced to 8 inches, a Flanigan.minimum for many herbs that would be suitable for a rooftop environment.The drainage layer is also similar to the Vegetable Garden prototype, but itsthickness is reduced to 1¼ inches. Figure 3-3 illustrates the green roof assem-bly and vegetation.B. Architectural RequirementsAn approximate load of 51 psf would result from installation of this proto-type.10 As an accessible garden, this prototype would be considered an occu-piable space, subject to code requirements for stairways and guardrails.9 Leopold Center for Sustainable Agriculture, Food, Fuel and Freeways, An Iowa Per-spective on How Far Food Travels, Fuel Usage, and Greenhouse Gas Emissions, June2001.10 All green roof loading estimates are based on the German green roof standard,“Guidelines for the Planning, Execution, and Upkeep of Green-roof Sites,” publishedby FLL (Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V.), 2002edition. 3-13
    • B AY L O C A L I Z E R o o f t o p R e s o u r c e s N e i g h b o r h o o d A s s e s s m e n tFigure 3-3. Cross-section of Intensive Green Roof—Herbs prototype.
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E SC. Maintenance RequirementsMaintenance needs would be significant and would include regular irrigation,pruning, weeding, fertilizing, and pest control. Irrigation needs would bereduced compared to the Vegetable Garden prototype, but a sub-surface dripirrigation system would still be desirable. As with all green roofs, regularinspection of the roof membrane would be required, and occasional repair ofthe membrane could prove necessary.D. Cost RangeGiven the cost variability factors that apply to all green roofs, it is estimatedthat materials and labor costs for this prototype would range between $28 to$40 per square foot, plus an additional $20 to $40 per linear foot for guardrailsand an optional $2 to $4 per square foot if irrigation is installed.11E. BenefitsIn addition to the environmental and social benefits previously noted, thisprototype would provide an ongoing supply of culinary herbs.11 Stephen Peck and Monica Kuhn, “Design Guidelines for Green Roofs,”http://egov.cityofchicago.org/webportal/COCWebPortal/COC_ATTACH/design_guidelines_for_green_roofs.pdf (accessed March 24, 2007). This estimate as-sumes that the prototype is applied when re-roofing is needed and therefore excludesthe cost of a new roof membrane. It also assumes that structural and architecturalrequirements of the Building Code are already satisfied. 3-15
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S IV. HYDROPONIC VEGETABLE GARDEN Hydroponics, also known as ‘organoponics’ in Latin America, is a horticul- tural method that supplies plant roots with liquid nutrients, eliminating the need for organic material that provides nutrients under conventional meth- ods. Plants are provided with nutrient solution, and are either grown in an inert mineral substrate or are suspended above the solution without substrate. The hydroponic model substantially reduces the weight of vegetable cropping systems by eliminating the growing medium. No fewer than six different techniques can be used to operate the system, some of which involve such equipment as water pumps, air pumps, comput-Commercial hydroponics. Source: Aaron erized monitors, timers, and lighting, when used indoors. This model of hy-Lehmer. droponics does not require artificial lighting as there is adequate sunlight for growing plants on the roof. The water supply is plumbed from the building to feed into the hydroponic system. A unique design component of the roof- top hydroponic prototype is a shade-cloth or light screen meshing as a ‘lid’ to protect the growing medium from being blown away in the wind. This re- taining cloth may be stapled along the edges of the container trays. A. Design Concept The Hydroponic Rooftop Vegetable Garden prototype utilizes a low-tech, low-cost method that minimizes weight while maximizing vegetable produc- tivity, variously called Simplified Hydroponics or Popular Hydroponic Gar- dens (PHG). The design is based on concepts developed and implemented around the world by the UN Food and Agriculture Organization (FAO), the UN Development Program (UNDP), and the Institute for Simplified Hydro- Rooftop hydroponics. Source: The ponics. Rooftop Garden Project, Alternatives, 2004. In this prototype, containers are filled with lightweight mineral substrate to a depth of 4 inches. Perlite is used as a base, and combined with inert organic material such as rice hulls, peanut hulls, grain chaff or coconut coir. The ad- 3-16
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E Sdition of these organic materials provides a more balanced substrate, thus fos-tering a healthier medium for the plants. This growing medium is ideal for itsextremely low weight, but it should be noted that other lightweight basescould be used, such as pumice. Appropriate plants include cooking and saladgreens, most summer and winter vegetables and herbs. Root vegetables canbe grown hydroponically but require greater substrate depths than specifiedin the prototype. Planting methods may vary among vegetable types, butgenerally seedlings are transplanted into the substrate, where they have regu-lar access to the nutrient solution.The prototype utilizes the “flood and drain” method of hydroponics, inwhich the nutrient solution is circulated back and forth between the growingcontainer and a reservoir container. The growing container is constructedwith a drain approximately one inch above the base, allowing for some accu-mulation of solution in the bottom of the container but draining the remain-der. If the growing container is elevated and placed at a minimal slope, drain-age can be gravity-fed. Alternatively, a pump can be used to continually floodand drain the growing container, recirculating the nutrient solution.Accounting for roof obstructions, pathways and storage areas, it is assumedthat growing area would constitute 60 percent of the total roof area. Figure3-4 illustrates the components of the prototype.B. Architectural RequirementsUnder normal conditions, the prototype would add approximately 9 psf tothe roof load. However, in a heavy rain event, the substrate may be saturatedand an inch of water could accumulate in the bottom of the growing con-tainer, resulting in a maximum load of approximately 16 psf.This prototype would be considered an occupiable space, subject to code re-quirements for access and guardrails. 3-17
    • B AY L O C A L I Z E R o o f t o p R e s o u r c e s N e i g h b o r h o o d A s s e s s m e n tFigure 3-4. Cross-section of Rooftop Hydroponic Garden prototype. Source: Based on designs in Bradley and Marulanda 2000
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E SC. BenefitsThe hydroponic prototype combines many of the benefits of the IntensiveGreen Roof-Vegetable Garden prototype with those of the Rainwater Har-vesting prototype. The prototype would appeal to residents as an attractiveopen space amenity. In terms of energy efficiency, the hydroponic containerswould shade the roof and vegetation would provide ambient cooling throughevapotranspiration, but the thermal mass benefits would be less than a con-ventional green roof. Generally, the prototype would not deliver energy effi-ciency gains comparable to green roofs.Instead of the storm water retention associated with green roofs or theground-level water storage of a rainwater harvesting prototype, the hydro-ponic system would capture rainwater in the growing containers and drain itto the reservoir containers for reuse. While centralized water storage wouldbe prohibitive due to excessive loading, this decentralized water storage acrossthe roof would distribute and minimize the load. Depending on the design,the Hydroponic prototype could capture and reuse all of the 14.3 gallons persquare foot of rainwater that falls in an average year. Additional irrigationwater would be conserved in dry months by recycling the water back andforth between the growing container and the reservoir container.In general, hydroponic systems represent a more productive growing methodthan conventional gardening. Because sufficient nutrients are supplied closeto the base of the plant, roots do not spread horizontally to satisfy their nu-tritional requirements. This growth pattern allows for closer spacing ofplants. In addition, hydroponically grown plants have an advantage over soilbased plants in that energy that would be expended in root growth is utilizedinstead for leaf, flower, and fruit growth. Based on estimates of the FAO, theHydroponic Vegetable Garden prototype would yield approximately 3-19
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S 4 pounds of vegetables per square foot.12 However, as this volume level is based on figures from professional hydroponic technicians, the actual volume may vary as much as two pounds less than the figures in this report. Typical field conditions can average a yield of 2.5 pounds per square foot.13 V. SOLAR PHOTOVOLTAIC ELECTRICITYUfafabrik factory in Berlin—Templehof green A. Technology Conceptroof research. Source: www.ufafabrik.de. Solar photovoltaic (PV) technology offers an opportunity to produce clean, renewable electricity on a wide range of residential and non-residential roof- tops. While the technology has existed for many years, recent advances are improving the efficiency of PV cells, which are the individual units that pro- duce electricity. These cells are combined into modules that are available in single crystal, multi-crystalline, and amorphous silicon (thin-film) varieties, differing in their efficiency and cost. Today, single crystal and multicrystalline systems are the most common and cost-effective types of installations. Single crystal and multicrystalline cells are comparable in most ways, though the former is generally the more effi- cient and the latter generally the more affordable. Both are commonly in- stalled in the Bay Area and both are considered “high-efficiency” systems. For the purposes of the PV prototype, the characteristics of the more com- 12 Charles Schultz, “Soilless in Singapore,” Growing Edge Magazine, http://www.growingedge.com/magazine/back_issues/view_article.php3?AID=17032 4 (accessed April 1, 2007). Juan Izquierdo, FAO. Personal communication with Brian Holland, DC&E, May 2007. 13 Willow Rosenthal, City Slicker Farms. Personal correspondence with Ingrid Severson, October 2007. 3-20
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E Smon multicrystalline type will be assumed. These panels have a typical gen-erating capacity of 1 kilowatt (kW) per 100 square feet.14Over time, other types of photovoltaic technology may become more attrac-tive options. Thin-film photovoltaics may become more cost-effective asmanufacturing methods improve, and advances in building-integrated photo-voltaics may one day make it possible to generate electricity affordablythrough building materials themselves. PV dealers and contractors should beconsulted to determine the most appropriate type of installation for a specificapplication and point in time.In addition to consideration of solar cell type, any PV system must be in-stalled with an acceptable tilt and orientation to be effective. Ideally the arrayshould face south, but southeastern and southwestern orientations are alsoacceptable. In applying the prototype on pitched roofs, assumed orientationis either southeast (135 degrees) or southwest (225 degrees). For flat roofs, theprototype has a southern orientation. Currently, public financial incentivesare directed toward electricity production during times of peak demand,which results in greater impetus for southwestern-facing installations. Onceagain, this condition may change over time as the structure of financial incen-tives will be a key determinant in the arrangement of any installation.With regard to tilt, an ideal tilt angle is that which sets the panel perpendicu-lar to the sun, which is the latitude of the location. The latitude of the StudyArea is 37.7 degrees north. While installing a PV system at an ideal tilt some-times involves additional cost, this prototype assumes that all arrays are set atthe area’s ideal tilt.14 Liz Merry, “Solar Electric System Basics,” Solar Energy Resource Guide, NorCalSolar, 2007. 3-21
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TR O O F T O P R E S O U R C E P R O T O T Y P E SB. Architectural RequirementsRoofs fitted with photovoltaics must be able to support the weight of a typi-cal multicrystalline PV panel and mounting hardware, which is approxi-mately 5 psf. The location should be mostly unshaded by trees or adjacentbuildings and panels should be set back from roof obstructions that cast shad-ows, such as enclosed stairway landings or mechanical equipment.C. Cost EstimateInstallation costs for a residential PV system in Oakland averaged $8.68/wattbetween 2006 and 2007 with rebates of about $2.50 per watt.15 While mostpanels have a power warranty of 25 years (meaning at year 25 they are guar-anteed to produce 80 percent of their original output), initial costs are oftenpaid back in only ten years, providing at least 15 years of no-cost electricity.16Inverters typically have a warranty of 10 years, and need to be replaced be-tween year 15 and 20. The cost of inverters has been decreasing significantlyquicker than the cost of the PV panels.D. BenefitsSolar photovoltaics can play an important role in a clean energy future, reduc-ing the region’s dependence on fossil fuel imports and mitigating greenhousegas emissions associated with natural gas power plants. In the near term,rooftop photovoltaics can also protect residents from rate spikes and reducepeak loads on the electrical grid, diminishing the need for costly and underuti-lized infrastructure to accommodate peak demand. Depending on the orien-15 NorCal Solar. “September 2007 Update and City Solar data spreadsheet.”http://www.norcalsolar.org/local-activism/bay-area-solar-installs-2007-6.html (ac-cessed October 10, 2007).16 Andy Black, “Payback and other Financial Tests for Solar Electric Systems,”http://www.ongrid.net/papers/PaybackOnSolarSERG.pdf (accessed April 1, 2007).3-22
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E Station, a 1kW module of the prototype is expected to produce between 1,278and 1,415 kilowatt hours (kWh) annually.17VI. RAINWATER HARVESTING AND REUSEA. Technology ConceptRainwater collection has been practiced for centuries as a way of stretching ascarce resource. Harvesting water from the roof is a simple and elegant solu-tion, powered not by electricity or sunlight, but by gravity. Since drainage isa standard component for most roofs, much of the infrastructure needed toharvest rainwater is already in place on existing buildings. In the U.S., rain-water is most often used for irrigation, less often for fire protection or toiletflushing, and rarely for potable water supply. This prototype will be de- Cistern at residence of Robert van designed for irrigation purposes as the most feasible use for the Study Area. Walle. Source: Robert van de Walle.Figure 3-5 provides a diagram of one potential arrangement of rainwater har-vesting components. The actual design of the system will depend on site-specific conditions.1. Catchment and ConveyanceThe first step in rainwater harvesting and reuse is to capture the precipitation.Typically, pitched roofs are fitted with external gutters and downspouts tocarry water off the roof and away from the exterior walls of the house. Inthis case, the prototype rainwater harvesting system entails installation of acistern connected to the downspout, intercepting water that would otherwise17 All calculations of PV capacity and production were generated in the “PV Watts”online modeling tool, developed by the National Renewable Energy Laboratory. It isavailable at http://rredc.nrel.gov/solar/codes_algs/PVWATTS/. 3-23
    • B AY L O C A L I Z E R o o f t o p R e s o u r c e s N e i g h b o r h o o d A s s e s s m e n t Leaf Screen Gutter Basket Strainer Down spout Screen Overflow Inlet Outlet 1.5" ball valveFigure 3-5. Diagram of assembly of rainwater catchment system Source: Courtesy of Southface (Atlanta, Georgia) using 50 gallon drum.
    • B AY L O C A L I Z E R o o f t o p R e s o u r c e s N e i g h b o r h o o d A s s e s s m e n tFigure 3-6. Diagram of integrated Rainwater Harvesting and Solar Photovoltaics prototypes.
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S reach the ground and run away from the foundation of the building.18 Leaf screens are installed at the gutter/downspout connection and at the down- spout/cistern connection to keep debris from clogging the system. A roof- wash system should be fitted to the gutter to divert the first flush of storm water, which may be laden with pollutants from the roof surface. While some flat or low-slope roofs have external drainage systems like the one described, others do not have drainage or use internal downspouts that drain directly to the storm sewer or to a ground-level discharge spout. In these cases, capturing rainwater is a more expensive proposition as the drain- age system needs to be modified with external conveyance equipment. 2. Filtration After collection and conveyance, several features should be incorporated to filter out roof debris and pollution before storage. A simple debris screen should be fitted to the gutter or downspout to catch leaves and other large particles. In addition, a first-flush diverter is commonly used to capture the first few gallons of rainwater during a storm, which is usually more laden with pollutants that have accumulated on the roof between rain events, such as dust and bird droppings. The first flush of storm water is then drained separately from the rainwater harvesting system. The recommended capacity of the diverter varies by roof type, regular presence of pollutants, and regular duration between rain events, but a general rule of thumb suggests one gallon of diversion capacity is a minimum for each 1,000 square feet of catchment area.19 18 Not all rain that falls on the roof will be drained, due to such factors absorption and evaporation. A runoff coefficient of 0.85 is assumed for pitched roofs in this proto- type, meaning that 85 percent of fallen precipitation will be conveyed into the rain- water harvesting system. The assumed runoff coefficient for flat roofs is 0.50, account-Rainwater captured for irrigation ing for pooling conditions or gravel ballasted roofs. 19at Stopwaste.org headquarters in Texas Water Development Board, Texas Manual on Rainwater Harvesting, ThirdOakland. Source: Sarah Sutton. Edition, 2005. 3-26
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E SAnother potentially necessary filtration component is the roof washer. Thisfeature is usually installed to filter smaller debris and organic materials. Manyroof washers take the form of a container with one or two canister filters in-side, installed directly before the cistern. The necessity of this componentwill depend on the type of irrigation system used; drip irrigation systems inparticular may become clogged if this type of micro-filtration is not em-ployed.3. StorageAfter catching and filtering the rainwater, it must be stored for later use. Residential cistern. Source: Marc Richmond.Storage is the limiting factor in this prototype, since space is often limited forinstallation of cisterns. Below-ground cisterns have been used for individualbuildings or community systems, particularly when they can be planned intonew construction, but the expense of excavation and pumping water back upinto the distribution system will prove cost-prohibitive for many residentsand building owners.Instead, this prototype assumes that above-ground cisterns are the most feasi-ble option in the Study Area. Cisterns vary in type and size. Plastic or steelcisterns are commonly available and are durable and movable. Reclaimedcontainers such as trash cans or steel/plastic drums could also be used. Cis-tern size would be based on the size of the roof, rainfall patterns, the amountof space available for siting and the proportion of rainwater versus municipalwater use that is desired. While some lots could accommodate a 1,500-galloncistern, others would be confined to a 500-gallon or even 110-gallon tank. Residential underground cistern inBased on observations of density and open space in the Study Area, an aver- Sausalito by 450 Architects.age storage capacity of 1,000 gallons is incorporated into the prototype. Source: Richard Parker.4. DistributionWater can be distributed to meet landscaping needs either through drip irriga-tion or watering by hand. Ideally, the cistern is sited at the highest elevationon the lot, enabling gravity-fed irrigation. This is often not the case in theStudy Area. If drip irrigation is used, a pump would be needed to pressurizethe system in some circumstances. 3-27
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TR O O F T O P R E S O U R C E P R O T O T Y P E SB. Architectural and Site RequirementsAs described previously, buildings should have an external drainage convey-ance system, most commonly found on pitched roof residential buildings.The site requirements for storage will depend on the size of the cistern. Di-mensions of storage tanks vary, but a circular 1,100-gallon cistern can measureas little as 6 feet in diameter by 6 feet in height, while a 55-gallon barrel can fitin spaces of just a few feet wide.C. Cost EstimateCosts vary widely depending on the need for new conveyance gutters andpipes, the size and type of the storage unit, the type of distribution, and thetype of labor used for installation. If reclaimed 55-gallon barrels are installedat existing downspouts and residents water by hand, costs can be as little as$100. On the other hand, storage tanks alone can cost between $0.45 and$1.00 per gallon, or $225 to $500 for a 500-gallon cistern.20 California-basedvendors sell 1,000-gallon, polyethylene tanks for an average of $550 with costsfor shipping averaging around $200. Plastic tank prices will fluctuate basedon the current petroleum market.21D. BenefitsThis prototype assumes a storage capacity of 1,000 gallons per structure,which would be stored for summer irrigation. Rainwater harvesting can cre-ate numerous benefits to water quality and water supply. These include:20 Ag Extension Communications, Montana State University,"http://www.montana.edu/wwwpb/pubs/mt9707.html (accessed April 1, 2007).21 Ingrid Severson. Phone calls to vendors, October 2007.3-28
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S ♦ Conservation of potable water. ♦ Conservation of energy required to deliver and treat potable water. ♦ Minimizing need for upgrades to water treatment facilities. ♦ Minimizing the stress on water delivery systems. ♦ Reduction of storm water runoff. ♦ Reduction of pollutants entering the watershed through runoff. ♦ Reduction of the thermal impact of runoff to wildlife and vegetation due to heat gain from the roof.Rainwater harvesting and associated water conservation are increasinglyviewed as critical responses to potential climate change impacts. Models sug-gest that the Sierra snowpack could decrease by as much as 70 to 90 percentand that early Spring flow from this source could decrease by 30 percent un-der a medium-warming scenario.22 Combined with growing demand, particu-larly in Southern California regions impacted by supply constraints of theColorado River Basin, these trends could stretch the region’s water supply indramatic ways. In response, rainwater harvesting offers a feasible and effec-tive means for conserving water and protecting water quality.VII. MULTIPLE PROTOTYPE INTERACTIONSThis section identifies opportunities and constraints for implementing multi-ple rooftop resource strategies in the same roof space. While there are manyunknown variables that influence these possibilities, research is beginning tolook at what type of synergies may come about through interaction of thesesystems. This section considers a few of the most likely interactions.22 California Energy Commission, “Our Changing Climate: Assessing the Risks toCalifornia,” July 2006. 3-29
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E S A. Extensive Green Roof and Photovoltaics This combination presents both positive and negative interactions, and exist- ing research has not adequately tested its feasibility. Installation of solar pan- els above the green roof vegetation would create a good deal of shade and would keep precipitation from falling evenly over the vegetation. Neverthe- less, some Sedum varieties have demonstrated shade tolerance, including Se- dum ternatum and Sedum telephium. Shading would reduce evaporation as well, potentially allowing for reduction of substrate depths beyond what is otherwise feasible in the seasonally arid Bay Area climate or the elimination of installed irrigation.Ufafabrik factory in Berlin—Templehof greenroof research. Source: Ufafabrik.de. A research plot maintained by University of Applied Sciences Neubranden- burg and the Technical University of Berlin has had success not only in green roof plant growth under a photovoltaic installation, but also in demonstrating increased PV output in this scenario. Their research indicates that green roofs can improve the efficiency of photovoltaics mounted above them. Ambient temperatures on the test plot were reduced 16 degrees Celsius compared to an adjacent conventional roof, which improved the efficiency of the PV and re- sulted in an average 6 percent increase in energy yields.23 The combined load of the Extensive Green Roof prototype and the Solar Photovoltaic prototype would be approximately 27 psf, precluding the possi- bility of combining these prototypes on existing buildings without structural retrofit. B. Green Roofs and Rainwater Harvesting Installation of these technologies in concert is technically feasible. Precipita- tion that is not taken up by the green roof vegetation is sometimes drained to 23 Manfred Kohler, et. al., “Positive Interaction Between PV Systems and Extensive Green Roofs,” Green Roof Infrastructure Monitor, Green Roofs for Healthy Cities. April 2007. 3-30
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T R O O F T O P R E S O U R C E P R O T O T Y P E Sdownspouts as in the conventional scenario. However, the cost-effectivenessof this strategy is questionable due to the retention and absorption capabilitiesof the green roof. Runoff coefficients of green roofs can range from 0.50 to0.80, allowing as little as 20 percent of the precipitation to drain into the wa-ter storage system.C. Photovoltaics and Rainwater HarvestingPhotovoltaic systems do not intercept or impede the flow of water from theroof, so these prototypes can usually be implemented together. Becausephotovoltaic panels do not absorb any water, the runoff coefficient of a rooffitted with an installation may be improved relative to that of normal asphaltroofing material, resulting in a marginally higher catchment capacity. In ad-dition, photovoltaic systems require periodic washing to remove dust and dirtbuildup and the wash water could be harvested under this scenario. 3-31
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TR O O F T O P R E S O U R C E P R O T O T Y P E S3-32
    • 4 FINDINGS This chapter presents the conclusions of the analysis, including discussion of how prototypes were assigned to each building and what considerations were not taken into account in the assignment process. The chapter also describes the benefits of rooftop resource development in terms of increased productiv- ity of energy, food, and water. Finally, the chapter concludes with a sum- mary of incentives for and barriers to future rooftop utilization. I. PROTOTYPE ASSIGNMENT Each building in the Study Area is assigned one or more rooftop resource prototypes. The following criteria are incorporated into the assignment proc- ess: ♦ Prototype Load and Roof Loading Capacity. Loading is a primary consideration in matching prototypes with suitable buildings. The analy- sis shows that the type of rooftop resource development that can take place on existing buildings is heavily dependent on the building type and associated loading capacity. ♦ Roof Access and Building Code Access Requirements. Access is an- other primary consideration in the assignment. The Intensive Green Roof and Hydroponic prototypes would be highly difficult to install and maintain without stair or elevator access. As occupiable spaces, these prototypes are also required by the Building Code to have stair or eleva- tor access. Therefore, the assignment of these prototypes depends on the existence or potential construction of a code-compliant stairway or eleva- tor. ♦ Occupancy Type. In some cases, more than one prototype would meet the above primary criteria for a building. Occupancy type is a secondary criterion that allows for consideration of what prototype the building oc- cupant would more likely choose based on its costs and benefits. 4-1
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G SThe following sections describe how buildings were designated with each pro-totype. Figure 4-1 illustrates the pattern of potential rooftop resource devel-opment in the Study Area.A. Intensive Green RoofBecause of the loads associated with the Intensive Green Roof prototype, itcould not be developed on any occupied buildings in the Study Area. How-ever, the prototype was assigned to the one parking garage in the area. Inaddition, nine vacant lots in the study area were identified that will likely bedeveloped over the next several years. As reflected on Figure 2-2, these lotswere classified as “Opportunity Sites” and were fitted with the IntensiveGreen Roof prototype. Because new construction developments can plan toaccommodate the load of a living roof, these buildings will carry this featuremore readily than existing buildings with a retrofit of a green roof.Advances in growing media may soon lead to the production of extremelylight-weight materials that can further reduce the weight of intensive greenroofs and allow limited vegetable production on existing buildings. At thistime, however, these products are not readily available in the San FranciscoBay Area.B. Hydroponic Vegetable GardenPost-war residential and institutional buildings are estimated to have the high-est loading capacities in the Study Area, ranging between 15 and 20 poundsper square foot (psf). The prototype adds a maximum of approximately 16psf to the roof load when applied across the entire roof area. However, theload is less than 15 psf when applied to 60 percent of the area, as specified inthe prototype.4-2
    • BAY LOCALIZE ROOFTOP RESOURCES NEIGHBORHOOD ASSESSMENT E. 19th St. d. Blv rk Pa E. 18th St. St . 8 th E. 1 E. 17th St.Lake Merritt Foothill Blvd. . vd Bl e or sh ke La E. 15th St. 1st Ave. 2nd Ave. 3rd Ave. 4th Ave. 5th Ave. 6th Ave. 7th Ave. 8th Ave. International Blvd. Clinton Square Park E. 12th St. E. 11th St. E. 10th St. 0 250 500 Feet Intensive Green Roof-Vegetable Garden Solar Photovoltaic with Rainwater Harvesting Rainwater Harvesting Hydroponic Rooftop Garden Solar Photovoltaic No Resource Study Area Figure 4-1. Aerial view of Study area with buildings assigned rooftop resources pototypes.
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G SThe limiting factor in this case is roof access. Buildings under four stories arenot required by Building Code to provide stairway access to the roof, andmost do not. At the same time, buildings with occupiable space on the roof-top are required to provide stairway access to the roof. The implication isthat many one-, two-, and three-story buildings are not currently equipped toaccommodate this prototype.For the purposes of the assessment, the following assumptions were made forflat-roofed buildings with adequate loading capacities: ♦ Buildings four stories and higher were assumed to have code-compliant stairway access since it is currently required, and are assigned the Hydro- ponic prototype. ♦ Two- and three-story buildings were assumed to have only ladder and hatch access and are not assigned this prototype. ♦ One-story buildings with adjacent open space were assigned the proto- type, with the expectation that a code-compliant external stairway could be installed at relatively little cost. The existence of adjacent open space was recorded during the field survey.These assumptions are necessary because roof access could not be determinedon a building-specific basis. However, a limited number of two- and three-story buildings may have stairway access to the roof and should not be ex-cluded from consideration in the future on that basis only.C. Extensive Green RoofLoading is the main constraint in retrofitting buildings with extensive greenroofs. The prototype, which was designed to minimize the green roof load,weighs approximately 22 psf. The strongest roofs in the Study Area haveloading capacities of between approximately 17 psf and 20 psf, found in post-War residential and institutional buildings. Therefore, it is likely that theonly cases in which extensive green roofs can be applied are those where addi-4-4
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G Stional dead load capacity can be obtained by removing pea gravel or rock bal-last from the roofs of these building types.Gravel has sometimes been used to surface conventional built-up roofs, wherelayers of felt and asphalt are built up from the roof deck. Just a few inches ofpea gravel are laid on top of the roof, weighing as little as 4 or 5 psf. How-ever, by reconfiguring this assembly with a green roof, that additional capac-ity may be obtained, potentially allowing for retrofit with the 22 psf exten-sive green roof. In other cases, heavier rock ballast has been used to secureloose laid single-ply membrane roofs, a roof type that has gained in promi-nence since the early 1980s. The commonly referenced standard for ballastedsingle-ply roofs calls for a minimum of 10 psf of rock ballast.1 If the ballast isremoved, additional dead load capacity is again generated, and the extensivegreen roof may become a feasible roofing option.The applicability of this approach will vary depending on location. It is pos-sible that very few gravel surfaced or rock ballasted roofs exist in the StudyArea, partly because of the age of the building stock (rock ballast was notcommonly used before the 1980s) and partly because of windy conditions thatmay have restricted their use in the past. More investigation and collabora-tion will be needed between engineers, roofing contracts, and code officials todetermine the feasibility of gravel or ballast replacement for green roof retro-fits.For the purposes of this study, the Extensive Green Roof prototype was notassigned to any buildings in the Study Area. In addition to the uncertaintysurrounding the cost and technical feasibility of gravel and ballast replace-ment and the prevalence of these roof types in the Study Area, it was deter-mined that the Hydroponics prototype was a more productive and low-coststrategy for rooftop greening on the buildings in question. Though extensivegreen roofs can also be installed on pitched roof structures of a limited slope,1 American National Standards Institute/Single Ply Roofing Industry, Wind DesignStandard for Ballasted Single Ply Roofs, November 19, 2002. 4-5
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G Sthese buildings were not designated with green roofs because they are alsomore suitable for other prototypes, such as solar photovoltaics and rainwaterharvesting.D. Solar PhotovoltaicsThe Photovoltaic prototype requires buildings with 5 psf of roof loading ca-pacity. The southern-oriented prototype was assigned to all flat-roofed build-ings with between 5 psf and 15 psf of loading capacity.All pitched roof buildings were designated with the Photovoltaic prototype.2With regard to orientation, the street grid and buildings in the study area areoriented 45 degrees off of north, so the prototype is for southeastern andsouthwestern-facing installations. The tilt was assumed to be ideal for thearea, at approximately 37 degrees, though installation costs can be reducedwithout substantially sacrificing performance by installing panels flush withthe pitched roof.The Study Area has high solar insulation with minimal shading, due to sunnyconditions, generally uniform building heights and an absence of maturetrees.E. Rainwater Harvesting and ReuseThe Rainwater Harvesting prototype was assigned to all pitched roof build-ings, including those with the Photovoltaic prototype, and to selected flatroof buildings. Pitched roofs shed water more efficiently than most flat roofs.2 It is assumed that all pitched roof structures in the study area will have adequate load-ing capacities for photovoltaics, and that usable roof space will average 40 percent forpitched roofs buildings and 40 percent for flat roofs, accounting for shading and roofobstructions.4-6
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G SIn addition, most pitched roof buildings in the study area are detached resi-dential units, which are assumed to have some open space to accommodatewater storage. Parcels with flat roof buildings were assessed for the existenceof adequate open space and only these buildings were designated with theRainwater Harvesting prototype. No buildings with green roofs or hydro-ponic gardens received the prototype.3II. OTHER CONSIDERATIONSA. Cost-Benefit AnalysisThe assignment methodology took into account the technical and regulatoryconstraints and opportunities for rooftop resource development and onlyused cost-benefit considerations as a secondary criteria. Clearly, however, anumber of financial factors will play a major role in determining how roof-tops are utilized. Initial costs bar many residents from taking advantage ofrooftop resources, despite cost savings that accrue on an ongoing basis foreach technology. Also, higher initial costs often correspond with higher im-pact technologies, such as solar photovoltaics or intensive green roofs.The cost-benefit calculus will inevitably change over time to reflect evolvingeconomic conditions and social values. For example, as government moves toreduce greenhouse gas emissions, it is possible that electricity will becomemore expensive due to market-based mitigation mechanisms like carbon taxesor cap-and-trade systems. Similarly, government may institute new incentivesfor rooftop resource development in response to citizen concerns aboutcommunity livability and sustainability. These incentives will change thedirection of rooftop utilization depending on their objectives.3 For pitched roof buildings, a runoff coefficient of 0.85 is assumed. Flat roof build-ings may have inadequate slope to drain most of their water, or could have gravel bal-last that would absorb water, so the runoff coefficient is reduced to 0.50 to reflectthese possibilities. 4-7
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G SWhile it is outside the scope of this study, analyzing the costs and benefits ofeach rooftop resource prototype is an important task that will assist buildingowners in making tough decisions about how to use their building to its full-est potential.B. SeismicityThe most prominent earthquake-related factor relating to additional roofloading is the existence of a soft story, as described in Chapter 2. This factorwas incorporated into the loading capacity assumptions used in the assign-ment process. However, for some individual applications of rooftop re-sources, additional seismic effects should also be explicitly considered ingreater detail.For instance, ground accelerations experienced during earthquakes causebuilding damage in proportion to the building’s mass. In general, additionalload that is less than 5 percent of the total building mass does not significantlyaffect the earthquake safety of that building. Many buildings weigh 50 psffor each level above grade. In this case, if 10 psf is added to the roof, the totalweight is increased by 20 percent for a one-story building and 5 percent for afour-story building. Thus, the seismic resistance of one- and two-story spe-cialty buildings (those which are not conventional wood construction) shouldbe explicitly considered by a qualified professional during an overall assess-ment of the roof loading capacity.III. PRODUCTIVITY OF ROOFTOP RESOURCESBased on the prototype characteristics and the assignment schema above, thetotal output of rooftop resources can be estimated for the Study Area. Theoutcomes of the exercise tell a story about what is feasibly achievable, in justone neighborhood of many, if a commitment is made to utilizing rooftops.4-8
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G STable 4-1 on the following page illustrates the application of prototypes andtheir benefits.A. Electricity from PhotovoltaicsIn the ¼-square mile Eastlake neighborhood, 8.5 megawatts (MW) of renew-able electricity capacity could be installed without sacrificing other rooftopuses that may be more appropriate. This total includes 4.6 MW on pitchedroofs and 3.9 MW on flat roofs. These photovoltaic installations would gen-erate over 11 million kilowatt hours (kWh) of electricity per year. With an-nual per capita electricity consumption of around 6,700 kWh,4 photovoltaicswould satisfy approximately 25 percent of the Study Area’s electricity de-mand under this scenario. Please refer to Appendix A, Assumptions andMethodology, for an explanation of the solar calculations.B. Vegetables from Intensive Green Roofs and Hydroponic GardensUnder this study’s scenario of rooftop utilization, 18 structures would be de-veloped with the Hydroponic Rooftop Garden prototype, and ten structureswith Intensive Green Roof-Vegetable Garden prototype, providing approxi-mately two acres of growing area. These gardens would yield approximately273,373 pounds, or 124 metric tons, of vegetables annually. This higher-than-average yield is the effect of year-round growing methods as well as hydro-ponic productivity greater than that of conventional methods.4 California Energy Commission, “Per Capita Energy Use by State in 2003,”http://www.energy.ca.gov/electricity/us_percapita_electricity_2003.html (accessedApril 18, 2007). 4-9
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G STABLE 4-1 PROTOTYPE ASSIGNMENT AND PRODUCTIVITY Number Total of Annual Prototype Structures YieldExtensive Green Roof 0 None 34.1 metric tons*Intensive Green Roof –Vegetables 10 of vegetablesIntensive Green Roof – Herbs 0 0 90 metric tonsHydroponic Rooftop Garden 18 of vegetables 11,609,024 kWh/year ofSolar Photovoltaics 668 electricity; 8.5 megawatts of capacity 1,869,000 gallons ofRainwater Harvesting 623 irrigation water* Productivity for the Intensive Green Roof. Vegetables prototype was derived from one exist-ing parking garage and nine existing, vacant lots (“Opportunity Sites”) that were projected asbeing built up with new structures integrating this prototype.Current annual consumption of the nutritional “dark-green leafy” and “deepyellow” vegetables included in the prototype is about seven pounds per cap-ita.5 Based on current consumption, the buildings with this prototype couldmeet this type of vegetable demand for approximately 38,127 Oakland resi-dents. However, current consumption of these vegetables is significantlylower than that recommended by the USDA, partly because of limited accessto affordable fresh produce. USDA recommendations for leafy greens anddeep yellows translate into about 31.6 pounds per capita. Using this figure,the garden prototypes could produce enough of these vegetables to satisfy therecommended consumption for approximately 8,500 residents, which is morethan the population of the Study Area itself.5 USDA Economic Research Service, Moving Toward the Food Guide Pyramid: Implica-tions for U.S. Agriculture, 1999, http://www.ers.usda.gov/publications/aer779/(accessed on April 1, 2007).4-10
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G SC. Irrigation Water from Rainwater HarvestingAccording to a report by the Public Policy Institute of California, outdoorwater use in the Bay Area averages approximately 0.19 acre-feet, or 8,276 gal-lons, per household annually.6 Approximately 26.9 million gallons, or 82.5acre-feet of rainwater falls on the roofs of the buildings assigned to the rain-water catchment prototype in the study area each year. If all of this rainwatercould be captured, stored and reused, outdoor water use needs would be metfor over 3,000 households, assuming a consumption rate at the state average.However, storing this volume of water would present an enormous technicalchallenge within an urban setting in that most of the storage would need to beinstalled underground, much of it in the public right-of-way. Large volumesof water storage are particularly necessary because 83 percent of Oakland’saverage precipitation falls between the months of November and March,while almost all of the irrigation demand occurs between the months of Apriland October.The quantity of water that can be stored and used as irrigation water usingthis prototype is more than just the 1,000 gallons of storage capacity, since thecistern will empty during irrigation and re-fill with the next rain. A commonmethod in calculating rainwater harvesting and reuse is the “water balancemethod,” in which monthly storage and demand are compared to determinethe balance of water that remains in the cistern at the end of the month. Forexample, a system may start with 1,000 gallons of water in the cistern, use1,400 gallons through the month, capture another 1,000 gallons during themonth, and end the month with 600 gallons in storage.However, use of this method requires an understanding of irrigation demandfor the specific site, while the purpose of this study is to estimate the potential6 Ellen Hanak and Matthew Davis, “Lawns and Water Demand in California,” PPIC,http://www.ppic.org/content/pubs/cep/EP_706EHEP.pdf (accessed April 15, 2007). 4-11
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G Sfor harvested water at the neighborhood scale. Without an understanding ofwater demand (that is, how large an area is being irrigated, what types ofplants and soils exist on the site, etc.), it is exceedingly difficult to quantify theamount of rainwater that can be stored and used. The best estimate, there-fore, relies on an assumption: that the harvested water is being used for alandscape that will require intermittent irrigation during the year, and thateach structures’ cisterns are filled and emptied three times in the course of ayear.This is a conservative estimate that assumes limited irrigation from Octoberthrough April, allowing the cisterns to fill up a total of three times per struc-ture, thus processing a total of 3,000 gallons of water in a year. If applied toall buildings designated with the rainwater harvesting prototype, the StudyArea could capture and use 1,869,000 gallons, or 250,446 cubic feet, of rain-water annually.7 This amount of water will be captured from 83 percent ofthe buildings in the study area, providing for a portion of the irrigation needsof each building.IV. STRUCTURAL IMPROVEMENT OPPORTUNITIESIn individual applications of rooftop resources, there will be some buildingsthat can support rooftop resources with additional productive capacity ifstructural improvements are conducted. This section describes a few of themost feasible retrofit options for various prototypes.7 Build it Green, Advanced Training Manual for Certified Green Building Professionals,February 24, 2007 e-mail from Marc Richmond, Practica Consulting, October 25,2007.4-12
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G SA. Extensive Green Roof PrototypeBuildings were identified that could potentially support an extensive roofafter conducting relatively minor improvements to or verifications of the roofstructure. Improvements were considered minor if they did not significantlydisrupt building operations and could be conducted for an overall cost on theorder of $10 per square foot of the total building area (2007 dollars).For wood buildings, such improvements could consist of sistering additionalrafters to the existing rafters. Buildings constructed of concrete masonryunits may only require installation or verification of steel beams. However,any proposed improvements to a particular building to increase its roof load-ing capacity should be designed by a qualified professional.B. Intensive Green Roof-Herb Garden PrototypeFor some buildings, if major improvements are planned, a few additionalstructural improvements could provide sufficient loading capacity for theweight of the Intensive Green Roof-Herb Garden prototype.One opportunity is to add to roof framing during a roof replacement. Manybuildings could feasibly support the weight of a shallow substrate intensiveroof if the structural roof framing is significantly supplemented. In particu-lar, a simple case is a steel building with bare metal decking at the roof butconcrete topping over metal deck at floor levels. Adding concrete topping tothe roof deck could increase the roof loading capacity substantially. This ef-fort may also require adding supplemental roof framing beams.When planning a seismic upgrade or other major renovation for any buildingtype, roof framing could be added as required to accommodate a heavier roofsystem. Many building types are natural candidates for seismic upgrades, ei-ther because of local mandates or because of documented poor response inprior earthquakes. These include: 4-13
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G S ♦ Unreinforced masonry (“brick”) buildings, for which California Senate Bill 1633 (introduced 2/2006) mandates safety upgrades. ♦ Concrete frame buildings constructed before 1975, which was prior to more stringent, ductile detailing requirements for reinforcing bars. ♦ Tilt-up (“big box”) buildings constructed before about 1990, which was prior to more stringent requirements for anchoring heavy walls to light- weight roofs. ♦ Steel moment frame buildings constructed between 1978 and 1995, which typically used heavy framing with welds that have exhibited brittle re- sponse. ♦ Soft-story or open-front buildings.Strengthening costs increase disproportionately if strengthening is requiredfor columns and foundations. In buildings of five stories or more, strengthen-ing existing columns and foundations may not be required if the additionalweight of a heavier rooftop system may be small relative to the total buildingweight. Likewise, buildings of two stories or less may not require columnand foundation strengthening if column and wall sizes were chosen for theirconventional size and are thus stronger than necessary. These conditionsmust be verified by a qualified professional before any additional load is in-troduced.Buildings on hard or stiff soils, which are not prone to liquefaction in anearthquake, are less likely to require foundation strengthening. Buildingswith little deterioration, including more modern buildings, will require lessstrengthening than a building with visible deterioration.V. POLICY OPPORTUNITIESThe results of the Eastlake neighborhood assessment demonstrate a profoundopportunity to utilize Oakland rooftops for economic development, envi-4-14
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G Sronmental sustainability, and food and energy security. However, a numberof financial and regulatory barriers lie in the way of rooftop resources devel-opment. This section describes incentive programs and code revisions thatcould spur a transformation in the way Oakland’s built environment con-tributes to its quality of life.A. Incentive ProgramsAs described previously, high initial costs limit the degree of implementationthat is possible for many residents. Local governments and service providershave a role to play in offering incentives for rooftop resource developmentwhen such strategies make good sense from a policy or financial perspective.1. Green RoofsCurrently there are few incentives offered for green roof installation. Own-ers that install green roofs may qualify for a federal tax credit under the En-ergy Policy Act of 2005, which provides a credit equal to 10 percent of thecost of insulation materials. However, State government has not institutedincentives for green roofs, nor does the City of Oakland offer programs orincentives for the technology. The City of Chicago, however, is a nationalleader in green roof implementation as the City offers direct incentives in theform of $5,000 grants for green roof installation on residential and smallcommercial buildings.Green roofs can be an asset to service providers, who may benefit by encour-aging wider implementation of the technology. For example, a green roof’sstorm water retention qualities reduce the volume of runoff that must be cap-tured, conveyed, treated, and discharged, thereby alleviating demand for newinfrastructure. In Germany, where approximately 10 percent of all buildingsare fitted with green roofs, storm water taxes are levied in many cities basedon the runoff generated by an individual property. While this type of taxmay not be feasible in the Bay Area, water districts like the East Bay Munici-pal Utilities District do benefit from green roofs and may find it possible tooffer storm water rebates to “low-impact” customers. Similarly, PG&E cur- 4-15
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G Srently offers rebates for a variety of high-efficiency appliances, insulation,high-performance windows, and cool roofs, but does not have a rebate forenergy-saving green roofs.Green roofs also can contribute to several points in the Leadership in Energyand Environmental Design (LEED) green building certification program.LEED is widely recognized for improving the performance of commercialbuildings and providing a marketing incentive to developers and buildingowners through its respected “green” brand. Depending on their design,green roofs can assist in obtaining points relating to improving energy effi-ciency, reducing storm water runoff, mitigating the urban heat island effect,restoring open space, and providing water efficient landscaping.Finally, developers in Portland, Oregon are able to increase their profitabilityby installing green roofs in exchange for bonuses in floor-to-area ratio (FAR).8This approach, sometimes called “amenity zoning,” utilizes zoning code pro-visions as additional incentives.2. PhotovoltaicsIncentives are available for solar photovoltaic installation at the State andFederal levels of government. California has been a leader in encouraging theadoption of solar technology, and most recently stepped forward to enhancesolar incentives through the $3.3 billion California Solar Initiative. The Cali-fornia Solar Initiative provides a rebate based on PV system performance.Currently, residential users receive $2.20 per watt of photovoltaic power in-stalled; in the Bay Area, this rebate is administered through Pacific Gas andElectric. Incentives for builders and developers installing photovoltaics onnew residential construction are also available through the California EnergyCommission. The CSI legislation also increased the number of customersthat are permitted sell their renewable electricity into the power grid. TheseState incentives are making residential PV applications, in particular, increas-ingly affordable. At the Federal level, businesses can receive a tax credit of 308 FAR is a standard measure of commercial density.4-16
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G Spercent of the PV system cost, while homeowners can receive a credit of upto $2,000.3. Rainwater HarvestingNo incentives for rainwater harvesting are available from local, State, or Fed-eral government. However, commercial buildings may be eligible for a rebatethrough EBMUD’s water conservation program. EBMUD’s Water SmartLandscape Rebate Program offers $1,000 for installation of high-efficiencyirrigation, but no rebate for rainwater harvesting systems on residential build-ings.Other cities in the U.S. are finding it desirable to offer incentives to encour-age water conservation and water quality improvements through rainwaterharvesting. For example, the City of Austin provides rebates of between $45and $500 for rainwater harvesting systems that provide irrigation water. ThePortland Bureau of Environmental Services provides $5,000 grants for“downspout disconnection,” which includes rainwater harvesting systems.B. Regulatory BarriersThere are few regulatory barriers to implementation of photovoltaic or rain-water harvesting strategies. As a newer technology, green roofs are not aswell understood, and in some cases regulations have yet to adapt to the designand construction industry’s enthusiasm for the technology.One barrier to adoption of green roofs is a lack of recognition of their bene-fits in current zoning codes. All open space is not equal, but very few codesspecifically reward installation of environmentally beneficial features such asgreen roofs. One exception is the City of Seattle’s new Green Factor pro-gram, which allows developers to meet open space requirements by choosingamong a suite of landscaping components, each with a corresponding pointvalue, instead of merely setting a minimum area requirement. Each compo-nent is assigned a value based on its benefits. Because green roofs are consid- 4-17
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G Sered a highly-beneficial approach, they satisfy a larger portion of the totalpoint requirement and enable an overall reduction in open space area. Thisreduction can maximize the amount of area that can be built upon and im-prove the financial performance of a project.In a broader sense, green roofs are a relatively new technology in the BayArea and code officials may need time to inform themselves of some of thetechnical considerations. Building codes do not necessarily discourage greenroofs, but for some municipal staff, questions may remain about code impli-cations. Part of this uncertainty results from the absence of a credible greenroof standard in the U.S.; the German FLL-Greenroof Guidelines, (For-schungsgesellschaftLandschaftsentwicklung Landschaftsbau e.V., Guidelinefor the Planning, Execution and Upkeep of Green Roof Sites, Release 2002) iswidely used but lacks regional applicability to the US and the Bay Area, andin some cases may not reflect the concerns of code officials. Fortunately, anASTM (American Society of Testing and Materials) green roof standard is indevelopment that will soon provide additional guidance to professionals indesigning, approving, and installing green roof systems.VI. CONCLUSIONThis neighborhood assessment shows conclusively that rooftop resources canbe developed on existing buildings in the Bay Area, without structural im-provements. In addition, new construction can be designed with increasedloading capacity, allowing for living roofs that are able to provide high yieldsof fresh, organic produce and underground cisterns with a generous capacityfor rainwater storage. Hydroponic rooftop gardens and solar photovoltaicsshow the most promise for existing buildings, while extensive and intensivegreen roofs and rainwater harvesting present additional challenges, some ofwhich may be overcome in time as greater investment is warranted. Today,building owners can install rooftop technologies and improve water quality,save energy, grow fresh produce, generate clean electricity, and contribute togreater community resilience and livability.4-18
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T F I N D I N G SEducation and leadership can bring about the kinds of benefits that so manycities have successfully demonstrated. Policy and government support areessential keys to fostering the implementation of these systems. Rooftops arecurrently untapped resources, and a package of appropriate design, develop-ment incentives, and public support is crucial to fulfilling their great poten-tial. 4-19
    • A P P E N D I X AASSUMPTIONS ANDMETHODOLOGY........................................................................................................................
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    • APPENDIX AASSUMPTIONS AND METHODOLOGYIn order to produce meaningful estimates of rooftop productive capacity,assumptions were made at each step of the study process. This appendixprovides background information on what assumptions were included anddescribes the methodology by which information was analyzed andconclusions drawn.A. Existing Conditions AnalysisExisting conditions were documented through a combination of aerialphotograph analysis and a field survey of the study area. A GIS (GeographicInformation Systems) base map of building “roofprints” was created based onthe aerial photograph and information about roof slope and existing rooftopresources was obtained from the photograph.A field survey was conducted by volunteers to document building types andconstruction characteristics. The volunteers were trained in simpletechniques for identifying building characteristics and ten groups were eachassigned a portion of the study area to walk and analyze. Collectedinformation was entered into the GIS database and correlated with estimatesof roof loading capacity.B. Estimating Roof Loading CapacityRoof loading capacity for each building type was calculated using thefollowing procedure:1. Unobservable structural properties, such as rafter size and spacing, were assumed for each type based on the building’s observed features and on the professional experience of the project team’s structural engineer.2. For each building type, a total roof loading capacity was calculated, corresponding to its assumed properties. A-1
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TA P P E N D I X A3. The code-level applied roof loading of 20 pounds per square foot was subtracted to obtain the remaining roof loading capacity.4. On a case-by-case basis, each building’s loading capacity was adjusted based on any special circumstances where an observable feature differed from the typical features of that type. Adjustments included:a. Age PenaltyBuildings constructed in an area other than that assumed for calculatingtypical properties were penalized to account for greater possibledeterioration. For example, if an apartment building matched all typicalfeatures listed in Table 2-1, except its construction era was pre-War, wesubtracted 5 pounds per square foot from the building’s loading capacity.This is because the material properties assumed for an apartment building arebased on mid-century construction.b. Height PenaltyBuildings with more stories than the typical range specified for that type werepenalized to account for the additional loading on the vertical load-bearingmembers, i.e. walls and posts.c. Construction Material AdjustmentFor a building whose primary construction material was weaker or strongerthan the typical construction material for that building type, the loadingcapacity was either reduced, in the case of weaker materials, or adjustedupward, in the case of stronger materials. Brick buildings that were assumedto be wood under their building type were particularly penalized.d. Soft-Story PenaltyA soft-story is a story level (usually the first story above grade) which hassignificantly less earthquake resistance than the adjacent stories. In anearthquake, the soft story will “sway” or “lean” much more prominently thanthe stiffer stories, and the earthquake damage will be concentrated in thatstory. Buildings with open fronts were penalized in order not to overload abuilding with potentially low earthquake resistance.A-2
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T A P P E N D I X Ae. Cumulative AdjustmentsIf a building had more than one adjustment, the adjustments were added(cumulative).Special consideration was given to buildings whose roof loading capacityequaled or exceeded 10 pounds per square foot, but did not reach the load ofthe Hydroponic prototype (16 pounds per square foot). For these buildings,a general average of 60 percent of rooftop area was designated for thehydroponic systems, assuming that the remaining area would require aprotective surface for human traffic. The surfacing for this prototype wasassumed to weigh five pounds per square foot. The consideration for thisdesign scheme would average less than 15 psf, given an averaging for thedistribution of weight between the hydroponic system and the pathways; thisenabled the Hydroponic prototype to be applied to many buildings withloading capacities of 15 psf.C. Productivity CalculationsA primary goal of the study was to estimate the quantity of food, energy, andwater that could be harvested from the Eastlake study area, and byextrapolation, East Bay neighborhoods in general. While some explanatorytext regarding these calculations is included in Chapter 4, and the Findingssection, the following provides a more thorough description of theassumptions and the calculations process.1. Extensive Green RoofDespite presenting a variety of other benefits, this prototype was not assignedto any buildings or analyzed for productivity because food, energy and waterare not produced on the extensive green roof. A-3
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TA P P E N D I X A2. Intensive Green Roof-Vegetable GardenNeighborhood-wide productivity in this prototype is a function of plantselection, growing area, and a “productivity coefficient” for each crop. Thecriteria used for plant selection is described in Chapter 3 and Prototypes. Thegrowing area was assumed to average 60 percent of the area of any roof,which is intended to account for mechanical equipment, vents, stairwaylandings and other roof obstructions, as well as space for paths to maintainthe roof and storage of maintenance equipment. This proportion was appliedto the total area of roofs designated with the prototype (61,232 square feet, or1.4 acres), to determine the total growing area of 36,739 square feet, or 0.84acres. Note that this calculation assumes development of all nine opportunitysite with intensive green roof vegetable gardens.Productivity coefficients for this prototype describe the amount of food thatcan be grown in a space of a certain size—for the purposes of this study,pounds of vegetables per square foot. Coefficients were derived fromUniversity of California Cooperative Extension data.1 These figures clusteredbetween 0.30 to 1.0 pounds per square foot for each harvest. To account forvariation in site-specific plant selection, and in recognition of the fact thatthere were no outliers to skew the outcome, the coefficients were averaged toobtain a typical coefficient of 0.62 pounds per square foot per harvest.Because a year-round gardening approach is assumed for the East Bay, thiscoefficient was multiplied by three growing seasons, resulting in an annualcoefficient of 1.86 pounds per square foot of growing area. By multiplyingthis figure by the total growing area above, an annual yield of 68,334 pounds,or approximately 34 tons, was determined.1 Nancy Garrison, Urban Horticulture Advisor, UC Cooperative Extension--SantaClara, “Home Vegetable Gardening,” http://vric.ucdavis.edu/veginfo/commodity/garden/tables/table4.pdf (accessed April 1, 2007).A-4
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T A P P E N D I X A3. Intensive Green Roof-Herb GardenThis prototype was not assigned to any buildings or analyzed forproductivity, but was included for the sake of testing options for lighter-weight edible garden prototypes, and could yield a perennial harvest ofculinary or medicinal herbs.4. Rooftop Hydroponic GardenYields for the hydroponic prototype were calculated on a similar basis as theIntensive Green Roof-Vegetable Garden prototype. Growing area was againassumed to comprise an average 60 percent of any roof designated with theprototype. Total roof area assigned the hydroponic prototype was 82,731square feet, or 1.9 acres. This resulted in growing area of 49,638 square feet,or 1.1 acres.The productivity coefficient was obtained from estimates by the UN Foodand Agriculture Organization, which has stimulated the use of PopularHydroponic Gardens (PHG) like the one described in the prototype in manynations, and was confirmed with the Institute for Simplified Hydroponics,which pioneered the use of PHGs in the developing world.2 Their initialestimate of 40 kilograms per square meter (8.2 psf) annually,3 however, wasbased on six annual harvests of lettuce as opposed to 3 annual harvests of leafygreens.4 The FAO figure was divided into a per harvest yield, then multipliedtimes three growing seasons to obtain an estimate annual yield of 4 psf. Thiswas multiplied by total growing area to determine the total annual yield ofapproximately 198,554 pounds, or 90 metric tons, of vegetables.2 Peggy Bradley, Institute for Simplified Hydroponics, personal email communicationwith Ingrid Severson, May 31, 2007.3 Charles Shultz, “Soilless in Singapore,” Growing Edge Magazine, retrieved fromhttp://www.growingedge.com/magazine/back_issues/view_article.php3?AID=170324 (accessed April 1, 2007).4 Juan Izquierdo, FAO, personal communication with Brian Holland, DC&E, in May2007. A-5
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TA P P E N D I X A5. Solar Photovoltaic ElectricityAssumptions regarding electricity output were based on regional sources andon the PVWATTS calculator produced by the National Renewable EnergyLaboratory. The first step in these calculations was to determine the roofsurface area that would be suitable for a photovoltaic installation. Becausebuildings were oriented 45 degrees off of north-south, it was assumed that halfof the area of pitched roofs (southeast and southwest faces) would havesuitable solar access. The total “plan-view” area of southeast or southwest-facing pitched roofs was 861,225 square feet. Total surface area of 1,148,212square feet was determined using a typical roof pitch angle in a trigonometricfunction. Based on aerial analysis and field observation, it was estimated that40 percent of this space, or 459,285 square feet, would be suitable for panelinstallation, due to constraints relating to shading and architectural detail.Finally, the area of flat roofs assigned the prototype was determinedseparately and multiplied by 40 percent to determine the suitable flat roofarea of 392,463 square feet.The next step was to determine an annual “productivity coefficient” forelectricity generation. The PVWATTS Version 2 calculator was used tocalculate annual kilowatt hours (kWh) of electricity produced per square foot,specific to the Eastlake area weather conditions. It was determined thatapproximately 12.78 kWh/square foot could be produced on southeast facesand approximately 13.59 kWh/square foot on southwest faces, assuming anideal tilt of 37.7 degrees. Southern-oriented panels could produceapproximately 14.15 kWh/square foot on flat roofs with panels orientedsouth. Of course, these estimates will vary depending on environmentalconditions at the site and on the specific equipment in use. However, thePVWATTS calculator is a widely-used tool that incorporates a variety offactors, including a DC to AC derate factor of 0.77 that considers differencesbetween Standard Testing Conditions rating and actual field performance, asA-6
    • B A Y L O C A L I Z E T A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P S R O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N T A P P E N D I X Awell as losses at the inverter, transformer, diodes, connections, AC and DCwiring, and losses due to soiling.5Using the productivity coefficients generated by the PVWATTS calculator,total annual electricity yield of 11,609,024 kWh was calculated for theEastlake area, produced by 8.5 MW of photovoltaic panels.6. Rainwater HarvestingDescription of the assumptions and methodology for this calculation wasincluded in Chapter 4, Findings. To reiterate, total “plan-view” area of roofsdesignated with this prototype was determined using GIS. Total catchmentcapacity was calculated by multiplying roof area by annual precipitation andapplying a runoff coefficient of 0.85 for pitched roofs and 0.50 for flat roofsto account for absorption, pooling and evaporation, and for spillage in theconveyance of water.6Catchment capacity is somewhat irrelevant, however, if cisterns and otherstorage infrastructure are not available to hold the captured water. Anaverage storage capacity of 1,000 gallons was assumed based on aerialphotograph analysis and field observation of available open space. This is thecapacity available at any one time, but over the course of a year more than1,000 gallons can be stored as water is used for irrigation, freeing upadditional storage capacity.As most rainfall in the Bay Area occurs from late fall through early springand the highest demand for irrigation water occurs in the summer, it isassumed that the harvested water will account for only a portion of theirrigation needs for individual properties. The water demands will vary upona number of factors including plant selection, solar exposure and soil type.Seasonal variations in rainfall and drought will also impact water need5 For more information on the PVWATTS Version 2 parameters, seehttp://rredc.nrel.gov/solar/calculators/PVWATTS/system.html.6 Email from Marc Richmond, June 24, 2007. A-7
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TA P P E N D I X Athroughout the rainy months. Therefore, a conservative estimate assumesthat the cisterns will be filled and emptied an average of three times per year,resulting in 3,000 gallons harvested per structure or 1,869,000 gallonsharvested annually and used for irrigation in the study area. To account forthese flows, a basic monthly water balance calculation was performed thatassumed all water captured could be usefully applied to the landscape betweenrains in the fall, winter, and spring, and the remainder of the captured waterwould be used in the dry season during the summer.A-8
    • B A Y L O C A L I Z ET A P P I N G T H E P O T E N T I A L O F U R B A N R O O F T O P SR O O F T O P R E S O U R C E S N E I G H B O R H O O D A S S E S S M E N TF I N D I N G S4-20