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Section 1; Chapter 2; Part 3; The Effect of Building Green on the Construction Process -- Materials/Specifications
--------Materials/Specifications-------- |
The following section provides deeper understanding of the environmental impacts of standard construction and how green products create benefits. Each aspect of green building, from foundations to finishes, involves specific environmental issues.
The choice of green material selection requires many considerations that have to be driven by good business sense. It should be a gradual process. It doesn’t serve you, your customers, or the planet if you go whole-hog building green from the start. That approach can have a serious negative impact on your bottom line. The question will always be how much can you afford to do? How many substitutions can you incorporate and still stay in your market niche? And how many changes can you make to ensure that when your children grow up they will have the same options of clean water, pure air, and deep forests you do?
Chapter 6 provides more specific information about green building features and benefits. At this point, however, it is important to take a look at the environmental issues concerning the materials used at each stage of the construction process.
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Foundations |
Concrete is technically a non-renewable resource, yet its component materials, stone, sand, and cement are abundant. Nevertheless, concrete, though highly durable, is extremely energy-intensive to produce and can cause high levels of air pollution. Concrete production is responsible for 8 percent of carbon dioxide production in the U.S.14 There are three aspects to concrete use: strategic placement, admixture components, and forming.
Strategic placement is using concrete where it is most important. For example, shallow frost-protected foundation systems are being used with success and code approval in cold northern climates like Fargo, North Dakota. There the frost line depth is 48", and shallow foundations are only poured 20" deep. It was pointed out earlier in this chapter that significant savings can be achieved by reducing the depth of the excavation and the yards of concrete poured.
Admixture components such as calcium chloride as an accelerator, gypsum as a retarder, and sulfonated melamine formaldehyde (SMF), a potential toxin, as a plasticizer, affect the environmental impact of the concrete. The impact may be on-site or at the plant, depending on the chemical. At the same time, some admixtures may be environmentally beneficial and enhance the concrete as well. For instance, fly ash (a by-product from burning coal in power plants) added to the mixture strengthens the concrete, reduces the amount of cement required, and recycles waste from industrial and utility waste-streams.TM15
Forming concrete can account for 15-35 percent of the total cost of concrete installations. Plywood has been the mainstay of concrete forming companies for many years. With plywood, the foundation essentially gets built twice, once in wood and again in concrete. To save on wood costs, some companies have invested in reusable aluminum forms. This is a more resource-efficient solution, yet it adds labor in building and dismantling forms. Reusable forms require form-release agents. Most of these agents are petrochemical-based and off-gas large amounts of volatile organic compounds. However, nontoxic vegetable-based form-release oils are available.
Currently, several alternatives to conventional concrete foundations use polystyrene foam boards to form walls. These come in a variety of shapes and sizes. The forms stay in place and serve as insulation for the foundation. Some foam products are treated with integral borate to deter damaging insects. Additionally, pre-cast concrete foundation walls are available in some areas. The advantages of pre-cast foundations are that they require less concrete than foundations which are site-cast, and they are designed to accommodate interior insulation.
Non-asphalt-based damp proofing reduces the risk of leaching chemicals into local aquifers and can last longer than conventional damp proofing. In some parts of the country, rigid mineral wool panels are available which help insulate foundation walls and provide effective drainage. Mineral wool typically includes iron-ore-slag (a postindustrial waste product). Recycled aggregate or crushed glass can be specified for use in the concrete or as backfill for foundation drains. To eliminate the need for periodic applications of pesticides, foundations can be designed with termite shields or back-filled with special termite-proof sand.
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Structural/Framing |
Wood is the most commonly used framing material. Large dimension lumber (2x10 and larger) is often milled from old-growth trees for economical harvesting and processing. However, old-growth trees as defined in this book are becoming more scarce and harder to access. Engineered lumber is now cost competitive for most applications. I-joists, oriented strand board (OSB), laminated veneer lumber (LVL), and trusses can substitute for dimensional lumber. Finger-jointed lumber in 2x4 or 2x6 studs is effective because it uses shorter pieces of wood that might otherwise have become waste and makes straighter lumber that is less likely to warp.
Light gauge steel framing can be used as a piece-for-piece substitute for wood, but it is not necessarily more environmentally friendly. Steel does contain some recycled content, but the light gauge steel used for framing generally has a lower recycled content than heavier steels. And all steel is energy-intensive to produce. Of even more concern is that steel is highly conductive, which may contribute to heat gain or loss, so it might be most effective for exterior framing in southern or moderate climates. It is most often used for interior wall framing in residential construction.
Masonry construction using hollow-core block masonry units (CMU) is difficult to insulate well. Autoclaved aerated concrete (AAC), a special kind of lightweight cement block, insulates better. With other types of block it is important to add insulation between the concrete block and the exterior finish.
Structural insulated panels (SIPs) are another wall framing alternative. These panels are usually made with OSB skins and foam insulation. They provide good insulation, are quite airtight, and go up quickly. Some panels substitute compressed straw for plastic foam as the core. Although these panels use straw that would otherwise go to waste, they do not provide the same degree of insulation as the foam-filled panels. Foam-core panels can also be used to fill in between post-and-beam or timber-frame structures. These heavy timber structures require large amounts of wood, but they tend to be quite durable. One way to conserve wood is to cut the post and beam timbers from demolished buildings.
Adobe, rammed-earth, straw bale and other less standard structural systems can be effective with good engineering and appropriate code approvals. Log homes, though, not only use excessive amounts of wood, but they do not insulate very well.
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Sheathing/Exterior Finish |
Sheathing, a secondary weather barrier behind the exterior finish, may serve as the primary substrate for attaching the finish layer and also provide diagonal bracing (rack resistance) for the structure. The exterior finish is the most visible material of the house and also the primary weather barrier. Relying on exterior finish as your only weather barrier can be risky, especially in regions with wind-driven rain or poor drying conditions. Wind and moisture will find their way into the smallest opening. Because of this, siding or exterior wall systems designed around the rain-screen principle are much more effective and durable. Such a strategy requires a vented exterior finish and a well-sealed secondary layer. Together, these layers work to balance the pressure on either side of the exterior finish, thus taking away the force that would otherwise drive moisture inwards or cause rot.
Plywood and oriented strand board (OSB) are the most common sheathing materials for residential structures. OSB, which is made from fast-growing trees of relatively low commercial value, uses a higher percentage of the tree. Plywood, on the other hand, needs larger diameter, often old growth trees to peel veneers efficiently. OSB uses a variety of sources for cellulose fiber and can incorporate various adhesive types that have different degrees of toxicity. Most OSB and plywood use phenol-formaldehyde adhesive that is less toxic than urea-formaldehyde, which is used in interior particleboard and some paneling. An OSB that uses non-formaldehyde MDI resin base for its adhesive is preferable.
Recycled content sheathing is also available. One option is a "sandwich" material using aluminum foil surface facings over a recycled wood fiber core. This sheathing meets most wind load requirements and costs less than OSB. Exterior gypsum sheathing, generally made with recycled newspaper, is an especially good option for stucco finishes
Redwood applied to the exterior is controversial in several ways. Clear heart redwood is generally cut from old-growth forests and therefore needs to be avoided. Some second-growth lumber is available; however, it is less resistant to rot and insects than heartwood. Sustainably harvested redwood is now available that protects the old redwood forests and provides high-quality material for a small increase in price.
For deck applications, pressure-treated wood has potential health consequences to installers and inhabitants because of the chromium and arsenic in CCA (copper chromium arsenate). Both copper and arsenic are toxic to humans. Recycled plastic lumber, especially when combined with wood fiber or other strengthening components, is another good alternative to CCA-treated lumber.
Recycled wood fiber (hardboard) siding and trim saves costs, is more stable than natural wood, and holds paint better. These hardboard products can lose durability in wet climates, though, if they are not installed properly.
Fiber-cement siding is extremely durable and looks like wood when painted. It is also fire resistant. The wood fibers lend elasticity and improve paint durability. Past problems with freeze-thaw damage in cold climates have been resolved.
Locally produced brick and stone can be excellent exterior choices. They are long-lasting, easy to maintain, and reduce transportation costs and environmental impacts. Molded cementitious stone, an alternative to natural stone, does not carry the environmental consequences of quarrying and transport associated with natural stone, but it adds to air pollution because it is made of cement.
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Insulation |
The environmental effects of insulation are greater than most other building materials. The level and quality of installation make a major difference in the amount of energy a house requires for heating and cooling. In general, more is better, and tighter is better, with a few caveats. For example, adding increased insulation to a ceiling is beneficial only if it is installed appropriately. A California study concluded that a 4 percent void in a fiberglass installation resulted in a 50 percent decrease in insulation effectiveness. In another study, one wall section was framed with wood 2x4s insulated with fiberglass batts; another was framed with steel 2x4s, insulated with the same amount of fiberglass, and sheathed in 1" foam board. Results showed a 35 percent greater heat loss through the steel wall section because of the thermal conductivity of the steel (Oak Ridge Study).
Fiberglass is the standard insulation in the industry today. High-density fiberglass makes the same wall cavity 15-20 percent more effective than low density R=11 batts in reducing heat loss. Fiberglass can incorporate 10-30 percent recycled material in its manufacture. However, the problem of microparticulate shedding (the release of invisible fiberglass particles that can irritate people’s skin, eyes, and lungs has become controversial). Loose fill is a greater risk than batts. In addition, fiberglass batts often use formaldehyde as a binder. Some newer products, though, employ alternative binders or no binders at all.
Cellulose insulation is environmentally friendly because it is primarily made from newsprint and recycled wood fiber from pre-and post-consumer waste. Another advantage is that when it is sprayed, it forms a good infiltration barrier, which adds to the tightness of the house and reduces drafts. It is less contractor- dependent for quality control in filling voids. Cellulose can be blown dry, mixed with a binder, or sprayed wet.
Rigid foam insulation applied to framing yields added infiltration resistance, reduced frame conduction losses, and added effective total wall R-value. Most rigid foams now are CFC free, using HCFCs as a blowing agent instead. Although much better than CFCs, HCFCs still contribute to ozone depletion and slowly out-gas over time from the insulation. As a greenhouse gas, HCFCs are 150-500 times worse that CO2 in contributing to global warming, though their work as insulator/energy-saver typically more than offsets their damage.16
Keep in mind that the more insulation installed in the house, the tighter the house becomes, the higher the possibility of creating indoor air quality problems. When your house is tested it should have greater than .35 air changes per hour (that is, the entire volume of air in the house is exchanged with outside air once every 3 hours). Anything less than that requires ventilation to provide fresh air to inhabitants.
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Roofing |
Petrochemical components are still used as the base for most residential roof composition shingle products. These products are not resource friendly, though, because they last for only 15 or 20 years and are rarely recycled. Forty-year shingles are a better choice. Alternatives are available in metal, plastic, and cement. These products use recycled content materials and come in shake or shingle-looking styles. Weight is an issue, though, with some of the cement-based roof tiles. Where hail is not a major threat, clay and concrete tiles are an option. All of the alternative roofing products have longer life spans than asphalt or fiberglass shingles and can be recycled.
A roof’s durability is of key importance. Not only can roof failure cause serious damage to the roof itself, water is often destructive to the building and its contents. Failures tend to occur at joints and penetrations, so not only must the roofing material be durable, but the whole underlying system must be stable, including flashing and edge treatments.
Roofing can reduce home cooling costs and can affect the temperature of the surrounding yard and even the neighborhood. A Department of Energy program aimed at lowering ambient outdoor temperatures in urban and suburban areas recommends that builders use light-colored roofing surfaces, which absorb less heat than conventional roofing. Along with ceiling insulation, reflective roofing can significantly reduce summertime solar gain into the building and thereby reduce the need for artificial cooling.
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Doors |
Exterior doors are basically solid wood or foam wrapped in metal or some other weather-resistant material. Doors with foam insulation, except those made from expanded polystyrene, contain HCFCs. Most insulated doors are similar in energy efficiency since the market is so competitive. The key component is good weather stripping and an effective threshold. R-values of 5-7 are common.
Interior doors are usually wood, molded hardboard, or hollow core. Luan plywood is harvested from rain forests, so it should be avoided. Molded hardboard is often made with recycled material and pressed into shape, but some is made with urea-formaldehyde and should be avoided. Solid wood is a beautiful value-added product, but clear stock is becoming harder to get and often comes from old-growth forests.
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Windows |
Windows are one of the most high-tech products in residential construction. Over the last 15 years the effective R-value of windows has increased by 50 percent.
This is the result of improvements in glazing and frame construction. The National Fenestration Rating Council publishes a book, The NFRC Certified Products Directory, that rates overall window energy performance.
Although they have been a standard for many years, aluminum windows are phasing out of most cold climate areas and are being replaced by vinyl frames due to vinyl’s higher R-value. Vinyl comes in a wide variety of qualities, however. Many frames have weather sealing problems over the life of the window due to expansion and contraction of the plastic. Some frame styles are prone to warping and sagging and are better suited to sliders and double hung styles than casements.
For energy efficiency, wood windows are still the standard, but manufacturers are facing the problem of finding affordable clear material with which to manufacture their product. Vinyl cladding adds value with its low maintenance qualities. Some manufacturers are using finger-jointed material with an interior coating and exterior cladding.
Low-E glass coating, which increases glass R-value from 2 to 3 is increasing in market share each year. The premium of 10-15 percent additional cost for low-E easily pays for itself in a few years. The added benefit is that in cold weather the window is warmer and therefore more comfortable to be near. Double low-E and HeatMirror are available in premium windows and can increase the R-value of the center-of-glass to 8.
Thought should go into placing low-E coated windows to maximize temperature regulation. In hot climates, choose coatings that transmit less solar gain. In cold climates, windows with glazing that allows more solar gain are desirable for south facing windows. East and west facing windows should minimize solar gain because sunlight is only intense in those directions during the summer. Thermal performance of windows can also be improved through using an inert gas such as argon or krypton between layers of glazing because these gases are less conductive than air.
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Flooring and Floor Covering |
Flooring should be durable to withstand daily use and to minimize the frequency with which it needs to be replaced. There is often a trade-off between hard floor coverings that are durable and easy to clean, and softer surfaces such as carpet, which provide more comfort and noise control, but tend to harbor more pollutants.
Vinyl tile and other sheet flooring products whose primary component is polyvinyl chloride (PVC) have the potential for VOC off-gassing. In addition, toxic by-products are produced in their manufacture. Natural linoleum, made primarily from flax and linseed oil, is an excellent substitute and one of the more environmentally friendly products available.
Ceramic and porcelain tiles are durable and therefore environmentally sound in the long run. Some high quality ceramic tile even contains recycled windshield glass in the glazing.
Carpet is a potential source of indoor air pollution, but a joint effort between the Carpet and Rug Institute and the EPA called the Green Label program identifies carpets that have reduced VOC emissions. A wide variety of high quality carpets are manufactured from recycled products such as recycled pop bottles (PET). Recycled content carpet has the performance and feel of conventional nylon carpet and is often more stain resistant.
Carpet tiles are another sustainable approach to carpeting because they can be replaced individually as needed. Carpet tiles also reduce waste and save money. These tiles often have a high recycled material content, and they can be resurfaced and reused. Some carpet recycling programs exist, and recycling usually costs no more than other disposal procedures.
The underlayment used between a sub-floor and floor covering is an environmental concern. Luan plywood, which is harvested unsustainably in Southeast Asia, is frequently used for underlayment, thus alternatives are preferred. Major tile manufacturers recommend a recycled-content, formaldehyde-free, gypsum-based underlayment.
When gluing down carpets, always use low-VOC adhesives or choose an alternative. For instance, you can use tack strips or a hook-and-loop tape system, which allows sections of carpet to be removed and replaced. A peel-and-stick acrylic adhesive is commonly used with carpet tiles.
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Paints, Coatings, and Adhesives |
These products, more than any others, can adversely affect indoor air quality, especially just after installation. The health hazard is particularly acute for installers. Most conventional products off-gas volatile organic compounds (VOCs), formaldehyde, and other chemicals that are generally used to enhance the performance and shelf life of the product. Medical research has raised concern, though, about the toxicity of combined chemicals on human health.17
Quality substitutions are now available for all these products. Some paints and adhesives use plant-based solvents. While these still off-gas VOCs, many people find them less troublesome than those emitted by petrochemicals.
Most VOCs from wet-applied products are released while the product dries, but they can continue to emit VOCs for long periods of time. Additionally, soft surfaces such as fabrics and carpets can absorb these VOCs and reemit them. To minimize extended release of VOCs, remove or cover all soft surfaces and employ direct ventilation until the coating dries.
For wood floor finishes, water-based urethane is suggested. This product contains no cross-linkers (a variety of toxic chemicals that add hardness). Other water-based finishes are also available. They can be as durable as standard solvent-based finishes, and installers often prefer them because they are less harmful to workers.
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Interior Finish and Trim |
Particleboard is a potential health problem due to bonding agents that use urea-formaldehyde, which can off-gas VOCs for years after application. However, an alternative medium density fiberboard (MDF) that contains no formaldehyde exists for cabinet construction and trim. Cabinets made with non-toxic materials and finishes, solid wood, and enameled metal are also available.
Clear material for wood trim is increasingly scarce and expensive. Finger-jointed material is generally available in most trim profiles when it is to be painted. For stain grade material, veneer coated, finger-jointed trim is available in several grades and wood species types.
Solid wood products, interior finish, and trim should originate from certified well-managed forests when possible. The Forest Stewardship Council and the Rainforest Alliance (Smartwood: See Appendix B for more information) are two U.S. organizations that certify forest operations. Again, because tropical forests are such delicate ecosystems, tropical hardwoods should be avoided unless they come from certified sustainable forests.
Continue to Conclusions
Would you like to purchase this book?
Building Green in a
Black and White World
by David Robert Johnston
Also See:
I. What is Green Building Introduction
II. Environmental Issues that Create the Market for Green Buildings
III. The Effect of Building Green on the Construction Process
IV. Conclusion
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