I’m currently in the middle of a full gut renovation of a single room in our 1904-built home in Wisconsin. The room in question is a former dining room which will become our new kitchen. We (my wife, dog, and myself) are currently living in our home as I take on a renovations one room at a time, with plans to eventually gut rehab most of the first floor and some of the second.

Here’s my question, how do I air-seal the shiplap sheathing from the inside now that the walls are open and the old plaster, lathe, and insulation are removed? Is closed-cell spray foam my only realistic option here? I’d prefer to avoid extensive use of spray foam given its high Global Warming Potential. One alternative that I have looked into is spayable caulking, specifically Knauf’s EcoSeal, which is mentioned by Martin Holiday in an article on GBA, https://www.greenbuildingadvisor.com/article/air-sealing-with-sprayable-caulk . While it seems anyone can buy these materials direct from Knauf, the minimum order size is an entire truck load – I’m assuming that’s a bit more than I’ll need.

The room’s dimension are ~12′ x 17′ with 10′ ceilings. Two of the walls are on the exterior, which totals about 290 square feet of exterior wall space, minus two new casement windows. The existing wall assembly consists of (from the outside in) vinyl siding, 1/4″ of blue foam board, the original clapboard siding (in very rough shape), a disintegrating layer of rosin paper, shiplap board sheathing, 2×4 walls with blown in cellulose, and the original plaster and lathe on the interior.  While I’m not aware of any major problems with water infiltration, the house is a bit drafty – especially around our windows (vinyl inserts in need of replacing).

Eventually, I would like to replace all of the siding and wrap the whole house in 4″ of polyiso and at that point would be able to airseal all of the walls at once from the outside, but that project is likely 5+ years down the line at the rate I’m working. Should I even bother trying to air seal the sheathing from the inside? Would it make more sense to just install rockwool batts and rely on the new drywall as the air barrier?