Want to insulate with no sheahting, but tar paper wrap
I just bought a 1962 house in Central Texas with mostly no insulation.
My contractor wants to add insulation to the exterior walls that we’re removing dry wall on (total about 1/4 of the house).
The exterior is: clapboard, felt paper, studs, then drywall.
In the article “Insulating Walls in an Old House With No Sheathing”, Martin suggest two approaches.
My question is if those approaches change if there already is felt paper between the cladding and the studs. Do I need an air gap in that scenario? Would I be safe just adding fiberglass batts?
Spray foam is out of the question for this remodel, to keep costs low.
Given that we’re only adding insulation to the part of the house, is it even worth it? Or should I just rip out the old fiberglass insulation in the kitchen and skip it all together?
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Walls are dry? no evidence of rain entry on the studs, sill plate or elsewhere? Decent overhangs on the house? Single story?
If you can answer yes to all, you could insulate it like your contractor suggests. Know that there is always risk. Rain exposure matters. Adding insulation will reduce the ability of the walls to dry.
The idea behind the air gap is to help facilitate drying but without a way to drain the cavity the only thing it can do is limit hydrostatic vapor drive through from the exterior. Coupling it with an air barrier does this more effectively but that is difficult to do from the interior. Martin's "cut and cobble" foam suggestion addresses this.
If you have mold concern, paperless gypsum board and plaster skim coat on the interior would be worth the upcharge from the drywaller IMO.