Air Sealing During Gut Renovation of a Single Room
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 in an article here, 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 or woodfiber board. At that point would be able to air seal 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 rock wool batts and rely on the new drywall as the air barrier? New dense pack and forget it? Cut and cobble foam?
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With a home that old, check if you have "honest" full-depth 2x4s. If the studs are actuall a full 4" deep, the easiest way to do a reasonable job air sealing is to cut pieces of 1/2" polyiso to fit tightly against the inside of the exterior siding boards, then seal it in place with caulk and/or canned foam. Once you've done that, you're left with a 3.5" deep cavity that regular batts will fit in. I'd use mineral wool batts to finish things off. If you insulate this way, you end up with a bit shy of R18 worth of cavity fill between the polyiso and the mineral wool batt, which is pretty reasonable. When you eventually replace the siding, you can add more rigid foam over whatever you use for exterior structural sheathing, then air seal that too.
Bill
Bill,
I like this suggestion. I double checked and my 2x4's aren't quite "honest" but they are closer than the modern stuff, 3-3/4" x 1-5/8". I suppose I can either compress the batts slightly or furr out the wall with some left over lathe to make up the difference.
Thanks for the input,
Jared
Even mineral wool batts should be able to be squished enough to deal with a 1/4" shortfall. I would specifically recommend the "Johns Manville" brand mineral wool batts here, since they are a little squishier than some others, and will probably be easier to use where you'll be compressing them in every stud bay.
If you want to furr things out, strips of luan stapled up to the edges of the studs will gain you just shy of 1/4".
Bill
I was thinking about just going with the 1" thick polyiso and furring out the wall 3/4" to make up the difference (4-1/2" thick total). It seems to me that installing 1/2" foam vs. 1" foam should be the same amount of work and I need to flatten the walls anyway so that my cabinets and drywall hang properly.
Also, looking into the pricing of polyiso 4x8 sheets locally (Menards) it seems that there's a premium placed on the thin 1/2" thick sheets ($20 ea), while the 1" and 2" sheets are priced more or less based on thickness ($25 ea and $50 ea respectively).
This approach should bump me up to an R-21 wall assembly for less than $100 extra in materials and not require much if any additional work.
If you can find a quality rental insulation blower, there are a lot of advantages to dense pack cellulose. It’ll be an easy job with the walls wide open. It’ll cost more than batts, but the gwp is far lower, it’s nearly harmless to work with, rodents don’t nest in it, and you’ll probably have a better air seal result than relying on drywall alone.
I’d avoid cut and cobble.
https://www.greenbuildingadvisor.com/article/cut-and-cobble-insulation
Norm,
I'm not really sure where to find a quality insulation blower, but apparently the low-powered blowers that can be rented from orange and blue can work if one is careful and knows what they are doing. (see, https://www.finehomebuilding.com/2017/01/20/cellulose-blowers)
The potential downside being that a cellulose installation using this method can only really hope to get to ~3.2 lbs/cu-ft instead of the prescribed 3.5 lbs/cu-ft, making it vulnerable to settling over time.
Does anyone here have experience with this type of "medium-dense" pack cellulose insulation installation?