Insulate stud cavities with the possibility to install exterior foam in the future
I am planning the remodel a 1920’s craftsman and wanted to get feedback on how to install the insulate in stages.
The building is a 1.5 story craftsman with a basement. The basement has a 2′ cripple wall. The wall framing is 2×4’s. Exterior to interior the layers are hardiboard, 1×12″ lapped plank sheathing, 2x4s 16″ OC with empty cavities, and then lath and 1/4″ plaster walls. The roof is an A frame with 2×8 rafters.
I live in climate zone 4C.
I plan to remodel the interior of the building first since the roof and siding are in good shape and would like to install exterior rigid foam 5-15 years down the line when the siding and roof need to be replaced.
The plan for the roof is to install rafter vents and fill the rafter bays with mineral wool then use a drywall air seal approach for the air barrier. The attic is a conditioned vented assembly currently and I would like to keep the living space.
My plan for the walls and cripple walls is to remove the lath and plaster, update the wiring and plumbing, install mineral wool insulation in the cavities, and then put up a double layer of drywall. The house is on a moderately busy street so the insulate and drywall is for both thermal and sound insulation. Again a drywall air seal approach for the air barrier. If building code requires a vapour barrier, then membrain sheeting behind the drywall.
Finally for the rim joists, installing rigid foam and filling the remainder of the volume with mineral wool.
With an old house I understand that insulating the walls with batts can lead to moisture problems on the sheathing or bottom plates due to condensation of internal humid air hitting the cold sheathing and the recommendation is to either use spray foam, or cut and cobble rigid foam. https://www.finehomebuilding.com/2016/05/17/insulating-walls-no-sheathing also recommends leaving an air gap. However, if I install foam (spray or rigid) in the cavities then when I go to put rigid foam on the exterior there will be a foam sandwich which could trap moisture between the walls.
The question is, what is the recommended approach to installing batts for an old home like this when rigid foam may be installed on the exterior at a later date. Should I leave an air gap for the walls to help with drying or use rafter vents in the walls to maintain the air gap? Would a vapour barrier be sufficient to prevent condensation on the sheathing?
Appreciate any advice or suggestions,
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