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Q.A winter's worth of rain fell on a large hillside home we're building before we could complete the roof. Though we tarped the project, rainwater seeped through the first-floor decking and into the floor framing of a basement wine cellar. I suspect that the fiberglass insulation we used to insulate the wine cellar's I-joist floor system is wet, if not saturated — but inspecting the joist bays and removing the insulation would involve cutting through the OSB subfloor or rim joists, since the floor is framed on top of the cellar slab. Now that the roof is completed, is it necessary to remove the wet fiberglass insulation and dry out the cavities, or will this wet assembly dry naturally without any intervention?

A.Paul Fisette, director of Building Materials and Wood Technology at the University of Massachusetts Amherst and a JLC contributing editor, responds: I would be concerned about the moisture trapped in the floor system and would take active steps to dry things out. When there are very low rates of air exchange, the primary drying mechanism is diffusion, which is pretty slow, particularly with relatively impermeable materials like OSB or plywood decking capping the floor system. Furthermore, not only is the wet fiberglass loading the joist bays with moisture, but so is the recently poured concrete slab — and it will continue to do so until the concrete fully cures.

Although the floor system will eventually dry out, there is considerable potential for mold and mildew growth in the meantime. Also, the OSB web material in the I-joists could swell irreversibly, possibly compromising the critical web-flange connections. Whether you go in through the top (through the OSB) or through the side (through the rim joist), the time and labor involved in drying out those wet cavities strikes me as cheap insurance compared with the potential costs if you don't.