Adding insulation to plaster walls – worried about moisture
Edmonton, Alberta, Canada. Zone 3b-4a. House is a 2×4 framed 1942 bungalow, 800 sqft + 750 in the finished concrete foundation basement. All the walls on the main floor are lath + plaster, basement is drywall (finished about 15 years ago).
We recently had the deteriorating stucco on the outside removed down to the sheathing boards, and replaced with tar paper + 1″ high permenace polyisocyanurate insulation (IKO ener-air, >1 perm WVTR) + vinyl siding to both improve look and hopefully make the place a bit more efficient. We wanted 1.5″ but the company ordered hte wrong material and didn’t realize til the stucco was all off, and we couldn’t wait the six weeks for new insulation in that state. So 1″ it is.
I still notice that the walls get fairly cool. Currently it’s -20 °C so we’re feeling it a bit. I believe that the house may have very minimal or even non-existent insulation in many of the exterior walls. This would be pretty typical of that vintage.
I’m curious about adding some blown-in cellulose, but there are some conflicting pieces of advice on this with plaster walls due to the possibility of moisture issues.
My question is basically this: while we have lath + plaster walls, the exterior is now updated in a way that (I believe) allows better vapour permeance and should mitigate issues with moisture retention. We do not have big roof overhangs, but with the siding we got the flashing updated as well which should help.
Would it be safe to add blown-in cellulose to the walls? Would it cause moisture issues?
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