A respected building scientist is raising concerns within the wood community by arguing that, in today's tightly sealed houses, engineered wood can make a home more prone to mold and moisture problems than does solid-sawn wood. The jury is still out on whether he's right, but in any case both he and the engineered wood industry tend to promote the same solution to fighting mold: better design and installation.
Joe Lstiburek of BuildingScience.com, a training and consulting company, presents his views on the issue in "A Material View of Mold," posted on the firm's website. In it, he argues engineered materials make more attractive food for mold. And while he has issues with all forms of engineered wood, he appears more concerned about particleboard than about I-joists and LVLs. "As we have moved down the process stream from timber, board lumber, plywood, OSB, hardboard, particleboard, to paper laminates–each step of the processing has made the products more water and mold sensitive," he writes.
The article also alludes to the issue of 'buffer capacity': the amount of moisture a material can safely absorb before that moisture starts causing problems for the building. Engineered materials have lower buffer capacities than solid wood, a fact Lstiburek says many builders fail to take into account. "The same amount of water we've always had to deal with is hanging around longer and longer in building materials that can't take it," writes Lstiburek.
As would be expected, the engineered wood community contests Lstiburek's views. "We have run independent tests and have reached very opposite conclusions to [Lstiburek's] very broad assertions," Boise Cascade says in a statement. "Our experience with our engineered wood products in the field does not support his assertions regarding [engineered wood products] and mold."
Marilyn LeMoine, communications director at APA, The Engineered Wood Association, notes mold "will grow on a variety of surfaces, both wood and non-wood, where there is excess moisture." In essence, APA says any wood product is going to have moisture problems given how some homes are being built today, and engineered wood products aren't more susceptible than solid-sawn wood. "It is inappropriate to place blame on the construction material for problems associated with the construction technique," LeMoine says.
Of course, engineered materials are here to stay; in fact, their resource- and cost-efficiency guarantees they will become even more prevalent. But this debate makes it more important than ever for dealers to recommend that their customers use construction details that keep water out of building assemblies, as well as give materials that do get wet a way to dry out. Barry Reid, a business development market manager at Georgia Pacific and a LEED accredited professional, says using engineered wood in a home without any thought to drying details is like putting a 750-horsepower NASCAR engine in a compact sedan: The chassis won't be able to handle the engine.
The APA has just updated its key document on controlling decay in wood construction and has an entire website, www.buildabetterhome.org, devoted to reducing moisture.
Builders should take extra care with window and door flashing details, shun complex roof designs that trap rainwater, and be more careful about draining groundwater away from foundations. Those who build homes over crawlspaces will be wise to consider sealing and tempering them. Lstiburek even suggests back-venting cabinets made from refined panel products.
Reid says homes in coastal areas that see a lot of wind-driven rain will benefit from more moisture resistant materials. That could mean using plywood sheathing rather than OSB because of plywood's greater mold resistance. In extremely damp environments, borate framing and panel products are an option, although they add cost to the building.
Long-term, the solution is for builders and their suppliers to understand how moisture moves through a structure as well as the role of air leakage, HVAC systems, and other factors. It means choosing materials wisely, protecting them from moisture, and giving them a way to dry out if they do get wet.
–Charles Wardell is a freelance writer based in Tisbury, Mass.
