Closed-Cell Foam in Wall Assembly
rhl_
| Posted in General Questions on
I have reposted this question as I think it was misunderstood.
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Ryan, as long as it's protected by drywall or something else for fire resistance, and it meets or exceeds your building code R-value requirements, I don't know of any code limitations for using spray foam in the wall. (There are hygro-thermal, occupant health and environmental concerns, however.) Why don't you think you can use it in the wall?
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Hi Ryan,
See https://www.greenbuildingadvisor.com/article/flash-and-batt-insulation. The closed cell in the wall is probably okay as long as its thin and/or the sheathing can dry to the outside.
If it's just a flash (looks like mist or spilled paint), it's not really a problem. If it's a fill in the wall, that's OK too as long as you're using it for insulation -- just finish the wall the normal way.
Where you might have some issue is if you have something weird like a half-filled wall. If the "half fill" is something like a 1" layer, just finish the wall off with similar insulation to whatever you're using in the rest of the wall and you should be OK. If the "half fill" is a full fill in the lower half of the wall only, then you have a weird assembly, but a batt above would still make things OK. Basically spray foam won't make the wall perform any worse compared to a full fill of batts, you'll just have to work the batts in around the foam.
Where you would have problems is if you have a "thick enough to count as insulation" layer somewhere that was going to remain exposed. If that's the case, I would remove the spray foam in that area unless you have a way to cover it to meet fire codes.
Bill
Bill, "flash and batt" or "flash and fill" refers to a layer of foam thick enough to provide dewpoint control, usually at least an inch or two, with the remainder of the space filled with fluffy insulation of some sort. Steve linked to a good overview above. Here's one I wrote ten years ago: https://www.finehomebuilding.com/2011/01/20/why-flash-and-batt-makes-sense. Half-filling the stud bays isn't weird, it's a smart way to reduce costs and climate impact.
True, but the OP's question doesn't really define what "sprayed a small section of wall" means. I was thinking it may have been by accident, and described a few ways I thought it could have been done. I probably should have mentioned "flash and batt", but was thinking more along the lines of overspray and not an intentionally installed layer. My first thought when reading the original question was that it's probably a full fill of part of a wall, which should be fine.
BTW, the "weird" half-filled wall would be a full depth fill of only half of the stud bay, a mistake, basically. I should probably have been more clear so that that wasn't confused with a half-depth layer over the entire area of a stud bay, which would be the "flash and batt" style installation.
Bill
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What is on the exterior? Can the wall still dry to the exterior?
Bill
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