Help with wall insulation/air barrier for rehab
A builder client is renovating a late 1800’s balloon-framed house. The house has clapboard siding with no wall sheathing. He needs to keep the siding per local ordinances. I suggested removing it and having it stripped of paint offsite and then reinstalling over new wall sheathing. Of course, he would rather not take my advise.
He does want to reframe the exterior walls to allow for more insulation. I also suggested this because the second floor joists have minimal support at a ledger board. He suggested using 2×6 framing placed adjacent to the full-dimension 2×4 framing. I have a couple problems with this. A large percentage of the wall will be wood framing and I need to retrofit some type of shear bracing.
I have thought about a few options.
Sheath the inside face of the original framing and install a new 2×4 frame wall inside of that. I would also call for an air barrier (taped seams?) at the wall sheathing. But I cannot get good insulation in a 2×4 wall. Going to a 2×6 wall takes up too much space.
Similar to above, but with two inches of closed cell spray foam placed against the back side of the siding.
Brace walls in another manner (let-in) and skip the wall sheathing. Then drape loose air barrier across the face of the original wall framing (with complicated details to seal top and bottom) an install R-19 batts in new 2×4 framing.
I would appreciate any thoughts of these options, or other possible options.
This house is for resale, so budget is limited. The house is in the Philadelphia suburbs.
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Replies
One option is to create 1/4-1/2” air space behind the siding to allow it to dry when it gets wet. Install 1/4-1/2” rod spacers against the back of the siding and the studs on both sides of the cavity, then install 2” rigid foam board sealed on all sides, and then finish cavity with fitted batts or blown-in insulation. You could add 2x2s to the studs and make the cavities wider for more insulation. It’s a labor intensive method, but tried and true in many historical renovations.
Other options for spacers could be 1/4"-1/2” boards cut in 1” strips, 1/4"-1/2" plwd cut in 1” strips, etc.
Mark,
Armando's suggestion is the usual solution.
This issue has been discussed several times on GBA's Q&A pages; here is a link to a previous thread on the topic: Insulating an old home.