Spraying foam in unsheathed wall
Now that we’ve paid off our 1890 house, we can start to do some of the deferred improvements. One big one is insulation. The attic’s straightforward – probably ‘glass batts – but I need advice on the walls. No way am I removing all the plaster and lath, so we need to blow in or spray in insulation there. Probably hire a contractor for this.
Conditions: unsheathed 1×10 v-groove channel rustic, in decent shape, outside. Lath and plaster inside; no vapor barrier. Mostly balloon frame, currently no firestops in most wall cavities; conventional platform framing on the additions (well, more or less; farmhouse construction, which means occasional creative framing like 2×3 studs sheathed inside with corral boards). House on the California North Coast, where winter is sometimes one long rainstorm. Moderate termite country, although we’ve had no trouble since having the house tented for drywood termites 25 years ago.
I don’t think I want to do blown-in cellulose, because we will no doubt need to open walls sometimes, and my son says it’s awful when you do – a cascade of fluff.
Of the types of foam, what would folks recommend? Urethane might add some stiffness to the walls, but I worry about blowing out the siding as it expands in curing. I’ve heard good things about icynene, but have no direct experience with it.
Replies
How cold and for how long are the winters there?
Attic insulation and a good tightening of the house against air infiltration might surprise you without
adding anything into the walls.
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From November through February and into March, we get a lot of below-freezing nights, down into the 20s sometimes; and days that don't break 50 degrees. Even though residents of Bemidji or Duluth would consider this balmy, it gets cold when it's 50 degrees inside the house in late afternoon after running the heater all day.
Without openning the walls, you are not talking about a spray on foam, but a pour-in. I have only read about it here, and have not known anyone using it yet.
I'm thinking I would use a BIBBs system - chopped fibreglas blown in blanket. It is much kinder to you if you tear things loose again later.
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I'm using icynene on a renovation on my house now. They have the regular spray on quick expanding and icynene also has the slow expanding pour in that I think they put into the walls through a few 1" holes in each cavity. In Eastern Mass., we have three icynene installers but only one will do the pour in as well as the regular spray. On that did not do the slow expanding said that there is not as much of a market for it and they do not like the risks of plaster cracking or similar problems. The cavity needs to be empty, it cannot have any old insulation, etc.