A. Contributing editor Paul Fisette responds: The problem, caused by moisture adsorption, is fairly common with stressed-skin panels installed on roofs. The panel edges take on moisture more quickly than the rest of the panel and swell as a result -- one of the shortcomings of OSB. What can happen with roof panels is that warm, moist air from inside the house leaks through the seams. As the indoor air cools, the moisture condenses and wets the panel edges. The moisture may also collect on the underside of the impermeable asphalt roof felt and shingles, compounding the problem. The solution is to meticulously seal the seams of adjoining panels with a product like spray urethane. Inject foam-in-place urethane into the seams before assembly or drill holes and fill the seams after the panels have been installed. Be careful about using spray-in-place urethane to seal panels in cold weather. The necessary heat of reaction is wicked away by the cold, which can interfere with the curing process and leave an unprotected seam. Check with the spray-foam manufacturer for recommendations on cold weather installations.
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