- 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.