moistureproof insulation for attic bath
i have questions about attic insulation for a bath in the attic–as in the recent article A MODERN BATH BUILT TO LAST. we are remodeling the attic in an old house and putting in a bath and bedroom. we plan on insulating the new inside walls with blown in cellulose product and originally thought we would do the same for the ceiling which in places does not extend to the roof decking but does extend to the roofdecking under the sloped portions. we were going to use baffles every other joist space to give ventilation. but after reading this article and the problems with mold, our plan may not be the best. for the bath ceiling, which in places could be insulated up to the roof decking, what do you recommend. can the closed cell foam be sprayed all the way to the decking without accumulating moisture?
this is an old house from the 1800s and has solid brick walls. in one area we have put some 2×4 walls in the kitchen and one of the baths and were planning on putting the cellulose sprayed into these walls. the contractor is a little concerned as the brick walls might sweat and collect moisture at certain times of the year and doesn’t know if the cellulose is ok or some other product would be better.
any advice from the editorial staff or anyone with firsthand knowledge of these problems would be a great help. thanks much. 28
Replies
What exactly is your exterior wall assembly to the interior?
Is it just brick and then studs with drywall/lathe on the interior? Or is there an exterior sheething attached to the studs between the brick and the interior wall surface? Any vapor barrier / diffusor?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
this is an old house built in the l870s and the exterior walls are three bricks thick with coats of cement and plaster on the inside (about 14 inches thick overall). the two by four studs were placed dirrectly against the plaster and there is no vapor barrier or sheathing, etc since this was not considered the "outside". the wallboard has not been attached yet and if necessary something could be placed in the space between the studs but the studs would still be in direct contact with the plaster or brick walls which theoretically could sweat. would closed cell foam board between the studs act as a vapor barrier? or should baffles be used on these walls as in the attic ceiling?
in the attic ceiling, there are places where i thought it might be advantageous to use the closed cell foam it it could be applied directly to the undersurface of the roofing deck without baffles. from your reply so far, i think baffles may be necessary. thanks for your quick replies and information 28
After you answer that last question, we'll be able to offer better advice.
But if you're blowing cellulose in the attic renovation walls, then go right ahead and blow the ceilings as well, including the slant ceiling/roof. But install vent baffles in every bay, extending above and below the insulation level. Even if you don't have good attic venting, having an air gap between insulation (of whatever kind) and the roof sheathing is critical to proper moisture management.
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