Market Intelligence

Green & Sustainable Construction

Green Wood Products

Certified wood should be used for any wood application for which it is available. Certified wood comes from well-managed forests that seek to balance the sometimes competing economic, community and environmental concerns associated with lumber harvesting and production.

Structural Support Members
Years ago, the dwindling supply of old growth timber spurred the wood industry to manufacture structural products that can be made with smaller diameter, lower-strength, faster-growing tree species. Engineered wood products include glu-lam beams, I-joists, and oriented strandboard. These products enhance quality control while reducing pressure on natural forests. They can make use of up to 80% of each log, as compared to solid-sawn lumber, which only uses about 50%.

Glu-lam beams are composed of wood boards glued together to create high-strength beams with depths ranging from 5" to 4' or more (depths and spans are limited only by shipping concerns). Similarly, prefabricated I-joists are more structurally efficient than solid joists, thus they require less wood. Engineered trusses are also an excellent option for creating predictable strength while reducing the amount and size/quality of materials required.

A potential downside of engineered wood is that it may contain toxic adhesives. Off-gassing of these toxins, such as formaldehyde, is particularly hazardous during curing in the factory (unless protective measures are taken), but still can be an issue after curing, especially for chemically sensitive people. These products may also release deadly gases in a fire. Fortunately substitute products are now available.

Sheathing
For applications that do not require high strength, sheathing products are currently available that are made of recycled wood fiber (up to 100%) and are themselves recyclable (up to 99%) These products use a relatively nontoxic bonding agent and are manufactured using less energy than oriented strand board (OSB) or plywood. To reduce air infiltration with any sheathing product, joints and edges must be sealed with air-barrier tape.

Decking/Outdoor Wood Applications
Traditionally, naturally rot- and insect-resistant redwood and cedar were used for outdoor applications. Unfortunately the popularity of these woods, combined with irresponsible logging practices, began to destroy the majestic old-growth forests in which they grew. Pressure treating wood with preservative made it possible to use species that were not naturally rot-resistant, but this produced other problems. Chromated copper arsenate (CCA) was the wood preservative most commonly used until 2003, when it was phased out due to its high toxicity to humans and other species, both during use and after disposal.

Fortunately, more sustainable alternatives exist today, including third-party certified redwood and cedar and wood treated with less toxic preservatives, such as alkaline copper quaternary (ACQ) and copper boron azole (CBA) for wood exposed to weather, or borate for wood not exposed to weather, but requiring pest-resistance. Wood treated with the copper-based ACQ and CBA should be avoided near aquatic ecosystems however, since copper is highly toxic to many aquatic organisms.

Though initial costs are higher, recycled plastic lumber and composites that comprise recycled wood fiber and recycled plastic provide a decking alternative with some performance advantages compared to real wood. These include reduced maintenance, increased longevity, and increased slip-resistance. They do raise a new set of environmental issues, such as the production and ultimate disposal of the materials used in their manufacture.

Other alternatives to preservative-treated or naturally rot-resistant wood include metal (especially for structural applications), landscape blocks or rocks for landscaping projects, and steel pilings filled with concrete (in lieu of creosote-treated underground pilings).

Excerpted with permission from Green Building: Project Planning & Cost Estimating, 2nd Edition, published by RSMeans.


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