A.Paul Fisette, director of building materials and wood technology at the University of Massachusetts Amherst and a JLC contributing editor, responds: Like any wood that is neither treated nor naturally decay-resistant, an LVL — which is typically made of southern pine or Douglas fir — will rot when exposed to excessive levels of moisture. In this case, the problem isn't the engineered wood itself, but rather the conditions that the LVL beams are exposed to. You're probably seeing rot at metal-connector locations and not in other areas of the assembly because the metal hangers are functioning as condensing surfaces and trapping moisture against the LVL beams. When the crawlspace air becomes saturated, condensation will form on the connectors first, creating the warm, wet environment that causes wood to rot.

To prevent this condensation, you need to lower the relative humidity in the crawlspace. The first step is to decouple the crawlspace from the damp soil. Whether the crawlspace is vented or unvented, it's critical to install a plastic ground cover over the soil. You can cover the plastic sheet with a layer of sand to hold the sheeting in place,...

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