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Wood in Buildings: Steps to Durability and Longevity


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Architects specify wood in their building designs for many reasons, including: cost, availability, ease of construction, thermal performance, aesthetics and design versatility. Research and new product development have only added to the versatility of building with wood. This presentation reviews how to use wood to its full potential. It discusses wood’s advantages in durability and longevity, while explaining issues of quality control for wood construction and the architect’s role in promoting such control. Finally, this explains how to maintain wood buildings and maximize performance.

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Wood in Buildings: Steps to Durability and Longevity

  1. 1. Wood in Buildings: Steps to Durability and Longevity How to Use Wood to Its Full Potential
  2. 2. AIA Best Practices reThink Wood sponsors this learning unit provided by Hanley Wood, a registered provider with the American Institute of Architects (AIA) Continuing Education Systems (CES). Credits earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion are available for recordkeeping and self-reporting purposes. This program is registered with the AIA; as such, it is not an approval or endorsement by the AIA of any material, product, or manner of construction. Questions related to specific materials and services should be directed to reThink Wood after you complete this learning unit. AIA Provider Number: K029 AIA Course number: BNSL1212 AIA Credit: 1 HSW/SD hour
  3. 3. Copyright Materials This presentation is protected by U.S. and international copyright laws. Reproduction, distribution, display and use of the presentation without written permission of reThink Wood is prohibited. © 2012, reThink Wood,
  4. 4. Course Description Specifying a building material considers structure, functionality and the aesthetics of the built project and environment. Architects specify wood for many reasons, including cost, availability, ease of construction, thermal performance, aesthetics and design versatility. Research and new product development have only added to the versatility of building with wood. New products enable increased dimensional stability, higher strength-to-weight ratios, and greater long-span capabilities. Keeping wood free from decay and pests is a function of following good design, construction and maintenance practices—all areas in which architects can influence the optimum use of wood to create buildings that benefit owners, occupants and the environment. Wood products generally have the lowest environmental impacts of the major construction materials used in the United States.
  5. 5. Learning Objectives  Discuss wood’s advantages in durability and longevity.  Describe strategies for moisture control.  Explain how to maintain wood buildings and maximize performance.  Explain issues of quality control for wood construction and the architect’s role in promoting such control.
  6. 6. Learning Objectives Section 1 DURABILITY AND LONGEVITY OF WOOD
  7. 7. Demand Durability To meet expectations for building durability, an architect should consider quality control such as detailing and maintenance techniques, as well as how the material is handled and installed. Photo: Stephanie Tracey 6-story mid-rise in the Pacific Northwest
  8. 8. Why Specify Wood? Reasons to Specify:       Cost Availability Ease of construction Thermal performance Aesthetics Design versatility Americana at Brand, Glendale, CA. Architect and photo credit: Togawa Smith Martin, Inc. Can be used in:       Single- and multi-story residential Schools Offices Industrial facilities Recreational centers Arenas El Dorado High School, El Dorado, AR. Architect: CADM Architecture, Inc. Photo credit: WI Bell, courtesy WoodWorks.
  9. 9. Design Flexibility      Light weight Workability Adaptable in field Well suited to additions and retrofits Can be dismantled and materials used elsewhere
  10. 10. Maximum Performance The performance of all building materials relies on proper detail to prevent bulk water intrusion and moisture entrapment. Tamarack Ski Lodge Heavenly Lake Tahoe Ski Resort, South Lake Tahoe, CA. Architect: Collaborative Design Studio. Photo credit: Carrie Compton.
  11. 11. New Product Development New Products: Benefits:      Increased dimensional stability  Higher strength-to-weight ratios  Greater long-span capabilities  Taller wood buildings Structural Composite Lumber (SCL) Glued Laminated Timber (glulam) Pre-fabricated paneling Cross-laminated Timber (CLT) Richmond Oval roof structure Architect: Cannon Design. Engineer: Fast+Epp Structural Engineers. Photo credit:
  12. 12. New Product Development  Stadthaus, London Architect: Waugh Thistleton  CLT Limnologen, Sweden Architect: Ola Malm  Forte Building, Melbourne Developer: Lend Lease Limnologen, Sweden. Architect: Ola Malm Photo credit: Midroc
  13. 13. Exceeding Expectations Architects can achieve superior results when they go beyond merely specifying wood to advocating for the right design detailing, construction, and maintenance techniques that enable wood structures to deliver decades, even centuries, of reliable service. Branson Convention Center, Branson, MO. Architect: tvsdesign Atlanta, GA. Photo by Brian Gassel/tvsdesign. Marselle Condominium, Seattle, WA. PB Architects. Photo credit: Matt Todd.
  14. 14. Longevity Study of buildings demolished between 2000 and 2003 in Minneapolis/St. Paul found no significant relationship between the structural system and building life. Wood buildings had the longest life span. Wood 63% of wood buildings 50+ years old Majority of wood buildings were 75+ years old Concrete Half of concrete buildings were 26-50 years old 1/3 of concrete buildings lasted 50+ years Steel 80% of steel buildings were <50 years old ½ of steel buildings were less than <25 years old
  15. 15. Service Life Potential threats to a long service life, such as moisture and insects, can be controlled with pressuretreated or naturally durable wood species. Western red cedar's unique properties make it ideal for weather-resistant applications. Photo credit: KK Law
  16. 16. Pressure Treated Wood “The longer the wood lasts the lower the costs of repair or replacement.” Dallin Brooks, WWPI  EPA approved preservatives  AWPA standards  WWPI CheckMark program identifies code compliant products and Best Management Practices for treated wood in sensitive environments
  17. 17. Section 2 MOISTURE CONTROL Branson Convention Center, Branson, MO. Architect: tvsdesign Atlanta, GA. Photo credit: Brian Gassel.
  18. 18. Natural Moisture Levels “All materials have challenges when it comes to moisture; however, when moisture is managed properly, wood exceeds expectations.” Cheryl Ciecko ALA, AIA, LEED AP  Wood and water are typically compatible  Wood can absorb and release moisture  If buildings are properly constructed, wood performs well in all types of climates  90% of North American homes are built with wood Wood shrinks or swells as its moisture content changes, but only when water is taken up or given off from the cell walls. Photo credit: Canadian Wood Council and Canada Wood
  19. 19. Moisture Content Moisture content (MC) measures how much water is in a piece of wood relative to the wood itself. MC <19% = Dry Wood MC > 28% = Fiber Saturation Fiber saturation is the point at which cell walls are holding as much water as they can. Additional water will go to the cell cavity where decay and fungi can utilize it. North America rain exposure zones. Courtesy, American Wood Council
  20. 20. Wood Shrinkage  The fiber saturation point is also the limit for wood shrinkage  Wood only shrinks and swells when it changes moisture content below 28%  Expansion and shrinkage occurs in the dimension perpendicular to the growth rings: ‒ Plates ‒ Band joists Photo credit: KK Law
  21. 21. Shrinkage  Longitudinal shrinkage is less significant, i.e. wall studs  Natural movement of wood is not problematic with proper design and construction but can become critical for wood buildings 6 stories and higher  Every 4% change in MC = 1% change in horizontal members  Engineered wood is drier and has lower shrinkage coefficients than lumber, but are more susceptible to water absorption
  22. 22. Humidity Control  MC of wood will stabilize in an environment with consistent temperature and relative humidity: ‒ Interior wood at 8-14% MC ‒ Exterior wood at 12-18% MC  This allows wood to perform its inherent humidity control function, releasing moisture in dry conditions and absorbing moisture when the surrounding air becomes humid
  23. 23. Dry Lumber  Start with dry wood and prevent moisture intrusion during construction and in building service  Shrinkage will have occurred prior to purchase – MC drops from 28% to 19%  Look for S-DRY or KD stamp
  24. 24. Moisture Loading  Moisture loads must be accounted for and balanced in building envelope design  Function of: ‒ Climate ‒ Surroundings ‒ Type of building  Managing Moisture Controls: ‒ ‒ ‒ ‒ Swelling Shrinkage Pests Decay Photo credit: Stephanie Tracey
  25. 25. Sources of Water Studies have found that a 4-member family can generate 10 gallons of water vapor per day. Exterior sources of moisture: Interior sources of moisture:            Rain Wind-driven rain Snow Irrigation systems Water vapor from outdoor air Building occupants Poor building envelope detailing Air leaks Plumbing failures Poor ventilation Poor thermal design
  26. 26. 4 Ds of Moisture Control  Primary objective of addressing moisture loads: ‒ Keep water from entering building envelope ‒ Balance relative humidity of indoor air with building  Moisture control achieved by following the 4 Ds: ‒ ‒ ‒ ‒ Deflection Drainage Drying Durability
  27. 27. Deflection  Rain deflection prevents rainwater from penetrating a wall and roof skin and entering the building envelope  Use these design features: ‒ Pitched roofs ‒ Overhangs ‒ Flashing ‒ Rainscreen
  28. 28. Drainage Drainage allows water that penetrates the cladding, roof shingles or other surfaces to flow along a water-resistant plane to exit building envelope. Rainscreen. 12/13/12
  29. 29. Drying Mechanism by which building envelope assemblies remove accumulated moisture by venting and vapor diffusion. In properly designed building envelope assemblies, water will evaporate and the resulting vapor will go through the assembly’s outer layers, providing vapor permeability has been designed into the building envelope assemblies. Photo credit: KK Law
  30. 30. Drying Exterior wall assemblies must be designed to allow sufficient drying to either the exterior or the interior, and the permeability of cladding, moisture barrier, vapor barrier and interior finish materials will greatly affect the wall’s overall drying potential.
  31. 31. Durability “Wood is not only our most valuable renewable resource, it is also prized as a versatile structural material. Its use in construction affects the environment in ways that are not always obvious, such as reducing the effects of climate change by storing carbon.” Carol Clausen, US Forest Service Forest Products Laboratory Richmond Olympic Oval, Vancouver, BC. Architect: Cannon Design Photo credit: KK Law
  32. 32. Fungi Control Understanding the conditions under which wood used in buildings breaks down is a first step in interrupting the process of decay and preventing wood deterioration. Overhangs protect end-grain of beams from moisture. Photo credit: Canadian Wood Council and Canada Wood
  33. 33. Fungi Control  Decay fungi deteriorates wood  Staining fungi gives wood a blue stain deep into interior of tree  Mold & Staining fungi feed off wood’s free water and sugars but don’t impair strength  Mold spores: ‒ Thrive in moisture & humid air ‒ Contribute to poor air quality ‒ Signal deficiency in a building’s moisture management program  MC <19% eliminates chance of mold growth  MC > 30% increases risk of mold  Most fungi grow fastest in 60-800 F range
  34. 34. Section 3 MAXIMIZING PERFORMANCE Campus Services Building, Western Washington University, Bellingham. Zervas Group Architects. Photo credit: Nic Lehoux
  35. 35. Materials Handling During Construction Materials handling during construction results in long-term performance of wood and the building envelope. “While an architect’s role typically does not extend beyond mere specification of wood to materials handling and construction practices, it would be ideal if architects did provide recommendations on how wood should be treated during construction.” Paul Morris, Research Leader - Durability and Building Enclosure, FPInnovations
  36. 36. Weather Protection During Construction:  Time delivery of wood close to installation date  Provide clean, well-drained material storage area  Inspect wood wrappers – replace with heavy tarp if faulty  Store 6-8” off ground away from ponding water  Place tarp or gravel pad on ground if soil is wet  Storage area free of vegetation
  37. 37. Weather Protection After Installation:  Protect structure from rain and other sources of bulk water  Install roof covering and moisture barriers  Ventilate materials in building envelope before installing insulation  Avoid premature application of interior membranes (gypsum)  Allow wood framing to acclimate and lower its moisture content If lumber has been significantly wetted during construction, schedules should allow for drying of framing and sheathing materials to19% or below.
  38. 38. Termite Control  Insects can cause significant property damage to wood, fixtures and fittings, furniture, cardboard boxes and books: ‒ Termites ‒ Carpenter ants ‒ Powder post beetles  Subterranean termites cause most damage  Total eradication is unfeasible so must contain existing insect populations and limit risk to buildings  Combat termites with 6-S Strategy
  39. 39. S-6 Suppression Reducing termite populations in a particular area and preventing spread to new areas. Methods:  Locating and destroying termite colonies  Burning infested wood  Heat treating reclaimed lumber
  40. 40. S-6 Site Management Careful site preparation and cleanup reduces potential for termite infestation. Methods:  Remove tree stumps and buried wood from site  Remove construction debris that contains cellulose  Drain water away from building  Remove wooden concrete formwork
  41. 41. S-6 Soil Barriers There should be no contact between the building woodwork and the soil or fill material. Methods:  Exterior woodwork 6” above ground  Pressure treat any wood in contact with soil  Establish a chemical barrier between the soil and wood
  42. 42. S-6 Soil Barriers Because of environmental concerns, chemical barriers in many instances have been replaced by physical barriers. Physical Barriers:  Precisely sized sand or crushed material beneath slab foundations  Termite mesh wraps foundation  Termiticide-impregnated membranes  Termiticidal bait systems
  43. 43. Slab & Foundation Details Slabs and foundation walls should be designed to inhibit the entry of termite and facilitate inspection of shelter tubes. Methods:  Cap CMUs or double walls with concrete or masonry  Keep exterior slab edges and foundation walls free of cladding for height of 150mm from finished soil level  Terminate exterior insulation and drainage batts 150mm below cladding  Cladding height should allow for landscaping  Raise untreated wood from ground Height above ground of non-treated wood elements. 1Based on the U.S. model building codes and American Forest & Paper Association recommendations.
  44. 44. Structural Protection  For many decades, preservative treated framing has been successfully used to deter termites  Wood products are also treated with borate, a water soluble chemical that is benign to humans, but kills insects that feed on it
  45. 45. . Structural Protection  While suitable for framing and sheathing, borate treated wood should not be used for outdoor applications such as decks and porches since the chemicals are water-soluble  A good quality coating, such as a three-coat filmforming finish, prevents the borate from moving out of the wood  Consult the American Wood Protection Association (AWPA) standards for borate and other preservative treatments under specific conditions and types of termites
  46. 46. Preservative Treatments  Pressurized ‒ Combination of pressure and vacuum achieve a deep, thorough chemical penetration ‒ Odorless water-borne option is paintable and stainable  Non-pressurized ‒ Brush, spray or dip wood in preservative ‒ Most building codes only allow field treatment for open side of a pressure treated member that has been cut  Termite resistant species: ‒ Heartwood of redwood ‒ Resinous heartwood of southern pine ‒ Heartwood of yellow cedar ‒ Cypress ‒ Western red cedar
  47. 47. Surveillance and Remediation  Regular inspections are necessary: ‒ Baiting ‒ Chemical fumigation or heat treatment  Both types of remediation must be done by licensed contractors  Do not protect against re-infestation  Vigilant monitoring is key to identify food sources and moisture The type of action taken against termite colonies will vary widely depending upon the type of termite, the location and the condition of the building. Protecting the structure by building with borate-treated wood products is a suppression option in certain situations. Photo credit: Louisianna-Pacific® SmartGUARD™
  48. 48. Code Requirements  Wood does not decay merely because it gets wet, but because fungi and insects consume the wood fiber as food  Critical to separate untreated wood from the ground and other moisture sources  Section 2304.11 International Building Code (IBC): ‒ Requires separation from soil level ‒ Addresses decay and termites ‒ Requirements for non-residential construction applications ‒ Requirements for wood used above ground for framing, decks, stairs, etc
  49. 49. Section 4 QUALITY CONTROL Ballard Library and Neighborhood Center, Seattle, WA. Architect: Bohlin Cywinski Jackson. Photo credit: Structurlam
  50. 50. Buildings That Work Every building material has its challenges, and despite the concerns outlined above, wood remains a sound choice in most situations. Over the years, experience has shown that the wood buildings that work over long service lives share several characteristics. Photo credit: Tien Sher Group of Companies
  51. 51. Dry Buildings Durability By Design: Store wood properly, design the building to keep the wood dry and observe proper maintenance practices Basements Because they are surrounded by soil, basement walls are subject to penetration by tiny amounts of water through concrete foundation walls that can cause wood to rot where exterior foundations don’t have a solid moisture barrier.
  52. 52. Buildings with Quality Assurance  3rd Party Inspection required for all construction materials covered by building codes  Chapter 17 of IBC, Structural Test and Special Inspections ‒ Specific construction practices critical to building’s structural capability  Treated wood products should: ‒ Be consistent with AWPA standards ‒ Carry the quality mark of an accredited inspection agency of the ALSC Photo credit: Jerry Parks
  53. 53. Regular Maintenance  Untreated, exposed exterior wood should be inspected 5 years after installation and every 2 years after  Sunken paint and surface collapse indicate wood decay  Inspect cladding annually for signs of wear and green algae stains  Examine through-wall flashing for brown stains  Properly paint or stain exposed wood  Re-treat with termiticides at appropriate intervals  Keep heavy shrubbery away from walls  Point sprinklers away from walls  Keep roof gutters unclogged  Promptly repair plumbing leaks
  54. 54. WOOD: A Material of Choice Because wood is versatile and long-lasting, it will continue to be the material of choice for many structural applications. Keeping wood free from decay and pests is a function of following good design, construction and maintenance practices—all areas in which architects can influence the optimum use of wood to create buildings that benefit owners, occupants and the environment. “Wood products generally have the lowest environmental impacts of the major construction materials used in the United States. In addition, wood is made from trees, a renewable resource that sequesters carbon while growing and stores carbon while in-use, thus helping to mitigate the impacts from climate change.” Richard Bergman, US Forest Service’s Forest Products Laboratory
  55. 55. Resources Use these resources for more information about building with wood:
  56. 56. Wood in Buildings: Steps to Durability and Longevity How to Use Wood to Its Full Potential
  57. 57. PROPERTIES On passing, 'Finish' button: On failing, 'Finish' button: Allow user to leave quiz: User may view slides after quiz: User may attempt quiz: Close Window Goes to Slide After user has completed quiz After passing quiz Unlimited times