vapor retarder/barrier use in Minneapolis
We’ve got 1950’s house and we are refinishing the kitchen. Wall assemblies in this home are 2×4 wood stud; interior walls are plaster on sheet rock; exterior wall is 1x ship lapped boards of varied widths (~12″?) which is covered with what looks like tar paper and then mediocre vinyl siding. No house wrap beyond the spotty tar paper.
Insulation within wall cavities is minimal (original) and in places someone appears to have blown in cellulose, however, I suspect coverage and density is spotty as our exterior walls have many cold spots.
There is not immaterial air movement through wall assemblies, which is something we endeavor to address over time, including correcting the house wrap situation when new siding is in the budget, possibly a couple years down the road.
I would like to remove existing interior wall finishing to install stone wool bat insulation, and then new sheetrock. My question is whether – given the current state of air permeability of the external wall side – we should be applying a vapor retarder or smart vapor membrane underneath the sheetrock. A number of years back I read a reference book for cold-weather building that suggested drywall glue, applied evenly and consistently along with effective air sealing around outlets, etc and a good latex pain was sufficient.
My concern is that during the Summer months, Minneapolis experiences notably high dew points often enough, paired with high temps. We use air conditioning and I am worried about moisture buildup within the wall cavity during the summer, against the vapor retarder/membrane, given the relative air “leakiness” of the exterior wall coverage for the next couple of years. I understand that a retarder or membrane will prevent vapor during the winter months from moving to the cold outside. As such wouldn’t a correctly installed retarder/membrane beneath sheetrock allow for moisture to not condense on the back of it and pass through the interior wall structure? Or am I grossly overthinking this…
thanks for any insights folks can share. Stevie
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