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Engineers Role In Green

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What role the structural engineer can play in designing a green/sustainable building.

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Engineers Role In Green

  1. 1. AN ENGINEERS ROLE IN GREEN BUILDING Green building is on all knowledgeable people’s minds today. Wikipedia.com defines it as: “green building is an outcome of a design which focuses on increasing the efficiency of resource use — energy, water, and materials — while reducing building impacts on human health and the environment during the building's lifecycle, through better siting, design, construction, operation, maintenance, and removal.” Groups ranging from the National Association of Home Builders (NAHB; www.nahb.org) to the National Kitchen and Bath Association (NKBA; www.nkba.org) offer ideas and programs to help design homes that are green. Another word associated with the green building movement is “sustainable”. What is the difference? NKBA expands on the above definition, delineating the two terms: “Understanding of Terms: Green is to be earth friendly. Sustainability, in the context of the environment, is to make use of processes and materials that can be maintained, reused, or recycled for an indefinite period in order to reduce and eliminate toxins while minimizing the negative impact on the environment.” To be sustainable is to be concerned with the amount and type of materials going into our buildings, whether they last a long time, can be from recycled stock, are re-used from existing stock, and can be recycled/re-used at the end of the buildings usable life. To be green, or earth friendly, encompasses the use of such sustainable materials in the larger context of the “use of goods and services considered to inflict minimal harm on the environment” (www.reference.com). The use of new materials can be considered green, even if not sustainable, when a larger view is taken, the larger view being a concern for the earths depleting resources. In a wider sense, Robert Gilman said: “In its broadest scope, sustainability refers to the ability of a society, ecosystem, or any such on-going system to continue functioning into the indefinite future without being forced into decline through the exhaustion or overloading of key resources on which that system depends.” In the context of this article, we will use the term green/sustainable to describe the type of home being built that inflicts minimal harm on the environment, uses fewer new resources, and is comfortable and healthy for the occupants. There is a myriad of construction methods available today. Some options include conventional wood frame of small dimensional lumber (2x4’s up to 2x12’s), timber frame, log, steel frame (from light gauge to structural shapes), concrete (as a frame or as bearing walls/roofs/floors), straw bale (either load bearing or as infill between a structural frame), rammed earth (in forms or stacked scrap tires), earth bag (a form of rammed earth), cob (another form of rammed earth using stacked balls/rolls of earth/clay), insulated concrete form (ICF; concrete poured into insulated forms that are not removed), structural insulated panels (SIPs; foam blocks sandwiched between sheets of structural plywood/gypsum board) to name a few. A modern home can be comprised of a combination of many of those methods. The foundation can be conventional or ICF concrete or wood (treated to resist moisture damage) bearing walls; the floor dimensional or engineered lumber, SIPs or concrete; the walls any of the frame methods, ICF, SIPs, straw bale, or any of the rammed earth methods; the roof dimensional or engineered lumber, SIPs or concrete. A future green/sustainable homeowner needs to become knowledgeable and educated in order to properly decide what types of home construction method to use.
  2. 2. An important consultant in the design of a green/sustainable home is the structural engineer. Wikipedia.com offers this definition: “Structural building engineering is primarily driven by the creative manipulation of materials and forms and the underlying mathematical and scientific principles to achieve an end which fulfills its functional requirements and is structurally safe when subjected to all the loads it could reasonably be expected to experience, while being economical and practical to construct. This is subtly different to architectural design, which is driven by the creative manipulation of materials and forms, mass, space, volume, texture and light to achieve an end which is aesthetic, functional and often artistic.” The reference to architectural design in this definition was kept to highlight the role that structural engineers play in green/sustainable housing design. Architects, while performing the important function of creating a pleasing space, do not always look at the most efficient use of that space regarding the structure that needs to surround it and protect the occupants from the loads applied, such as snow, wind, water, seismic, and occupant loads. Many times an engineer has been consulted with long after the design is “set in stone” only to be told that he must make it work, often by using more stones. While certain goals and criteria of the occupant’s needs and desires should be maintained in the design, these can be manipulated for more efficient use of materials. A recent design we participated in included a large lower level garage with covered parking outside the garage doors. A concrete deck was included over the garage and parking area to make that space usable and to allow the homeowners a panoramic view of their surroundings. The homeowner wanted some rooms added, which were placed in the deck area. The result placed loads from ICF concrete walls and roof over the garage and parking area, with no place for supporting columns. Hence, many large steel beams, the size of those used in high rise buildings, needed to be used to support the loads between column locations spaced far and few between. When this was pointed out to the homeowner, the response was that the design was too far along to significantly change. We were able to convince the homeowner to use lighter weight SIPs walls, transfer roof loads to other bearing points, use a lighter weight wood framed deck with a roofing membrane, and to place a few columns in locations that he could live with. Despite that, there were still beams over 25’ long supporting more beams over 25’ long supporting loads, which required those skyscraper sized steel beams, for a residential project. Bringing the structural engineer on board early in the design can eliminate many of these problems when they most easily can be dealt with, before the “stone” stage. Structural engineers, by our training and experience, are able to look at a design and quickly assess the basic structural load path shape (how the loads are carried by the structural frame to the ground), spot critical areas, and draw attention to structural issues, whether major or minor. This is best done in the schematic phase of the design, coordinating with the designer and homeowner the optimal layout for their individual goals and criteria. A description of the design phases that an architect employs are as follows: The Programming, or Gathering Information, phase is where an architect spends time with the homeowner to determine how their current space is adapted to the way they live now, to better understand how future changes will suit their needs more directly, and finally a list of intentions and rough sketches of spatial adjacencies (what areas are adjacent) specifically derived from the homeowner and the building site is prepared; the Schematic Design phase is where the architect formulates a concept - a theme - which
  3. 3. turns the written description and adjacency diagram into spatial definition; Design Development phase is where the architect and the homeowner continue to define - through plans, elevations and sections - the size of rooms, types of materials, and exact placement of the building; the Construction Document phase is where a set of detailed documents are prepared. According to architectural standards, this set informs the builder of the appearance and construction detail of the trim, built-ins, doors, and surface elements, with no mention made of the structural system (italics added). It is vital that the structural engineer become involved prior to layout of the rooms and major spaces, the Design Development phase, during or just after the Schematic Design phase, when the design can be reviewed with an eye to the structure supporting all loads surrounding those spaces. In the previous example, the design could have been changed to accommodate the extra rooms while providing for a simpler load path, eliminating the use of more structure than was needed and still meet the needs of the homeowner. This is especially important in green/sustainable construction, where the homeowner has hade a conscious and informed decision to do their part in assuring a future for coming generations by a reduced use of the earth’s resources, whether in construction or operation of their home. Again, in reference to our previous example, extra steel material was needed to meet the same needs of the homeowner that could have been met if the structure had been structurally reviewed earlier. This homeowner had to spend more money, both in material and labor, to build his home. That impact was directly felt, or will be when the construction invoices come in. In the larger picture, that spelled out by Robert Gilman and embraced by all concerned with our and our children’s future, our houses need to be built without the construction materials being “forced into decline through the exhaustion of key resources”. If even a small percentage of the homes designed use extra materials, that will quickly add up to resources that are not available for the rest of us on the earth. Looking beyond our national borders, groups such as Engineers Without Borders (EWB; ewb-usa.org) an international group of engineers helping those in developing countries achieve basic needs of water, sanitation and education, will not have steel available for water wheels to transport water to the fields for food production; Habitat for Humanity International (habitat.org) will not have the materials to provide basic shelter to those in developing countries; this highlights just two of the groups helping others who will not be able to continue their work. What this actually means is that mankind will not be able to continue to exist and flourish if the resources we depend on are prematurely depleted. Participate in responsible green/sustainable design by consulting early in your design process with a structural engineer, and the earth will smile upon you. The “new” alternative construction methods mentioned earlier carry the same external loads as conventional construction, but the load paths can be significantly different. A structural engineer experienced in and willing to work with such construction methods is an invaluable member of the design team. Different materials carry loads in different ways: load bearing straw bale walls can not sustain even a small point load and must have a load spreader element on top of the wall; rammed earth walls of all types can carry a limited point load and must have the same load spreader, or an integral load carrying vertical element; SIPs can carry high uniform loads, but also need an integral load carrying vertical element for point loads; all of the alternative methods have their individual idiosyncrasies which must be understood and properly designed for. The loads
  4. 4. paths need to account for where the loads act on the supporting elements. A wide wall, such as straw bale, tire, or rammed earth, cannot simply bear on the outer rim of the floor, which in turn is resting on possibly an 8” wide concrete wall. If that load path is not considered, the floor joists may easily become overloaded to the point of failure. The different types of methods also exert unique loads according to the weight of each. A conventional 2x6 and drywall/siding wall 8’ tall weighs 120 pounds per linear foot (plf), while a straw bale wall exerts up to 320 plf, and rammed earth walls can exert 800 plf. These must be accounted for in the design. There are many experienced architects and designers available who can lay out a design making the best use of your alternative materials: straw bales are between 3’ and 4’ long; wood panels are 4’ wide; tires are an average of 30”-32” diameter; ICF forms come in 48” to 96” lengths with 12” to 16” stack heights; all of these need to be accounted for in the dimensions of the home to avoid unnecessary cutting and fitting. They are familiar with room layout to make the best use of the space you have. They can design in essential elements such as proper window locations to make the best use of daylighting and natural ventilation. They can lay out the utilities so that heating and plumbing runs are efficient and not oversized. There are many factors that come into play in the design of your green/sustainable home. However, only a structural engineer can assure that it will safely withstand the forces of nature, and do so in the most efficient manner possible, with the least use of our earth’s resources. Contact a knowledgeable structural engineer early in the process of designing your home, and you will have the “greenest” green/sustainable home available. Mark Benjamin, P.E., M.ASCE, SECB is president and principal engineer for Crown Jade Design and Engineering, Inc., a structural engineering firm specializing in green/sustainable housing design; his son David, VP of Drafting, can work with you to produce all the architectural and structural plans necessary to obtain a building permit and build your new green/sustainable home. See us on the web at www.crownjade.com; email jademail@crownjade.com; or contact us at 970-472-2394.

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