Wood Frame Construction
Most houses and apartments in the U. S. are still built from wood, using two-by-four- or, more and more commonly, two-by-six-inch studs. Nailed together 16 inches apart, these pieces of lumber form the wooden "skeleton" over which stucco or siding is placed.
Wood is a sustainable product - we can grow more trees to replace those we cut down. Unfortunately, we can no longer depend on the old-growth forests that used to supply our needs. Clear, virgin lumber, once plentiful and inexpensive, has become increasingly more costly as demand for it has increased. In response, the construction industry has developed new building techniques using new products made from young trees and scraps of wood that once would have been discarded.
Forest management practices have changed, too. New trees are often planted to replace those cut for lumber, helping to sustain a supply of wood for the future.
By being a knowledgeable consumer, you can insure that wood framing is as efficient and ecologically sound as possible. Consider these suggestions:
- Avoid larger-sized framing members such as two-by-tens or two-by-twelves. These mature woods often come from old growth forests. Instead, use engineered wood products such as trusses and I-joists. Made with low-grade fiber, small-diameter trees and fast-growing, less-utilized tree species, engineered wood products and value-added products can actually perform better than lumber alone. Consider products such as "I" joists, oriented strand board, (www.osbguide.com/bconstruction.html) laminated veneer lumber, finger-jointed lumber, open-web wood joists and trusses, stressed skin wood panels, and wood/steel joists.
- Try to purchase domestic wood - commonly used in most construction and interior finishing - that is produced through sustainable forest management. Although the source of lumber can be difficult to determine, an increasing number of lumber producers operate sustainably and participate in third-party certification programs. Other programs are being developed specifying a sustainably harvested wood standard in building construction.
- Consider using salvaged timber and wood products available from operators who disassemble old buildings and bridges and then clean, grade, and often resaw the timber.
Air Quality Problems with Wood
Wood is subject to damage by insects and by dry rot. By saturating lumber with chemical preservatives applied under pressure, manufacturers can help it to resist damage caused by moisture and termites.
There are two basic ways to pressure-treat wood. The first - more an industrial application - treats lumber with the preservatives creosote and pentachlorophenol. Utility poles or railroad ties are the popular examples of wood treated with these heavy-duty chemicals.
Homeowners use a more common type of pressure-treated wood that is preserved with inorganic arsenic. Usually southern yellow pine, it is the primary material in outdoor structures such as decks and fences.
An important word of warning - don't use pressure-treated wood indoors! The wood-treating industry claims that, when properly treated and allowed to dry, pressure-treated wood is safe to handle and the chemicals will not leach out of the wood. Nevertheless, it should only be used on outdoor projects. Don't burn scraps of the wood, especially in a wood stove.
While manufactured wood products often perform as well or better than lumber, glues used in the manufacturing process can cause substantial indoor-air-pollution problems. Engineered wood products made with exterior-type glues (phenolic resins) and urethane (polyurea) adhesives give off some of the lowest emissions.