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Insulating from the outside - Help! 1899 Farmhouse (no sheathing)

Posted: Wed Dec 30, 2020 2:42 pm
by midatlanticus
I’m Rob. I’m in WV (Climate zone 4/5). My 1899 has no sheathing, true 2×4 studs, poplar dutch lap siding. I’m trying to balance energy efficiency, cost consciousness, with historic preservation. Because the original siding must be removed for some repair/replacement, I’m tackling the project from the outside. (Original wall and ceiling beadboard makes insulation from the interior unworkable.) I have several original double hung windows that will stay so I prefer to find a way to limit my challenges around windows by adding several layers. I also prefer to avoid spray foam on the original structural timbers in the interest of future restoration. If it’s the absolute best option in my situation I’d consider spray foam if I can protect at least the backside of the wall beadboard.

Is it possible for me to put mineral wool matts (Rockwool) into the stud cavity, use a quality weather vapor barrier and then reapply siding? Will I need to use fir strips or other form of air gap. I’m hoping to avoid adding sheathing or at least minimalize the impact that adding space to the exterior wall will have around my windows.

Thanks for the guidance. I’ve seen lots of advice of tackling this scenario from the interior. From the exterior, I’m hoping to gain energy efficiency while also limiting the “build out” of the exterior wall. It’s asking a lot, I’m sure. What ideas do you have?