Building a Better Wood Than Mother Nature

By Katherine Salant
Saturday, May 17, 2008

I recently asked several builders, "Which building product with recycled content gives the biggest bang for the buck?"

They were nearly unanimous in their choice -- but the product they cited does not have recycled content, according to the manufacturers. It does have many other green attributes, though.

That product is engineered wood, a man-made material that performs much better than the real thing -- the new-growth framing lumber now available.

Engineered wood looks different from regular wood. When home buyers first see it, they might think their builder is pulling a fast one because it does not look like the exposed framing in Grandma's attic.

Engineered-wood products appear to be made of randomly placed wood chunks mixed with brown goop. The chunks are actually lumber strands that were shaved off a log, coated with wax and resin, carefully layered, and then heated under pressure. The resulting products are stronger than new-growth lumber, straight rather than twisted and dimensionally stable: They won't warp, crack, or shrink and swell with seasonal change. All these things are hugely important to a home builder.

Engineered lumber can be shaped into the form of every traditional piece of framing, as well as some that will startle home buyers walking through their house as it goes up. For example, floors are now routinely supported with I-joists that are similar in profile to the steel I-beams used in high-rise construction.

From the street, the most visible engineered-wood components are 4-by-8-foot sheets of oriented strand board, commonly called OSB. It is used for the roof decking and wall sheathing that enclose the house.

What makes engineered wood green? First, it's made with tree species that were previously considered to be worthless and left to rot in the forest. Second, it can be made with small-diameter trees -- as small as six inches -- that grow in as little as seven to nine years, leaving stands of old-growth forest for future generations. Third, no wood is wasted in its manufacture. The entire tree can be used, including the bark.

Although it is possible to frame an entire house using only engineered lumber, most builders still frame walls with traditional 2-by-4 wood studs -- single pieces of wood sawed from a tree log -- because these are less costly and the quality of lumber for smaller pieces is satisfactory.

Because of its moisture resistance and dimensional stability, engineered wood is being used on the exterior as finish siding and trim. As this application will be permanently exposed to the weather and permanently on view, very little softwood is used. Preservatives to prevent rot, termites and fungi are added to the mix. Once these exterior products are painted, they look like traditional wood.

A product with recycled content that several builders mentioned but few buyers would ever think about is the concrete used for foundation walls and floor slabs. As much as 50 percent of the cement in the concrete mix can be switched out for fly ash, which is coal waste that accumulates at electric power plants. Besides recycling a waste product that would otherwise end up in a landfill, the substitution can give the concrete added strength. About a third of the 100 million tons of fly ash produced each year in the United States is used for concrete.

Reducing the cement in the concrete mix also benefits the atmosphere. Cement manufacture is such an energy-intensive process that it accounts for 3 to 5 percent of global greenhouse-gas emissions.

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