insultating rim joists, redux

[EricU]

the 1st floor joists in my house are 16" on center. So at both ends, the rim joists are really hard to get to. I'm thinking on the chimney end, the only way I'm going to be able to insulate those cavities is using foam. I doubt someone is going to want to come in and do 8'x16" worth of foam. The boxes of foam scare me a little. I know some people on here have used them. Is spraying blind into a cavity like that going to work? The opening is almost exactly filled with a 2x4 (1.5 high, 3.5 wide)

[Splinter Puller]

They have a wand tip to inject the foam deep into a recess. You have to be aware of foam expansion issues though.

[EatenByLimestone]

Foam is combustible. You don't want it touching your chimney. Code says 2" air space. In that air space I stuffed kaowool and then smeared firesafe caulk over it for an air seal.

[EricU]

thanks, hadn't thought about the chimney

[Snipe Hunter]

If the house is ever sold and there is exposed spray foam, the inspector will note it on his report as a possible fire/safety hazard. Just like exposed foam board. There is nothing wrong with it if it is covered with sheetrock, or even plywood.

Some foams claim to be fire retardant and they may be but the inspector won't make that determination.

[Scoony]

Snipe Hunter said:

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If the house is ever sold and there is exposed spray foam, the inspector will note it on his report as a possible fire/safety hazard. Just like exposed foam board. There is nothing wrong with it if it is covered with sheetrock, or even plywood.

Some foams claim to be fire retardant and they may be but the inspector won't make that determination.

---

So I am also doing this with foam board. No chiminy to worry about. I dont have plans to refinish the basement at the moment. Originally it had the fiberglass mats stuffed in there, and I still have those pieces. Do I need to put them back in front of the foam board?

[EricU]

I'm putting the ceiling back up in this particular area, so no problem with that. I think I've heard of people putting drywall up to hide the rim joist foam insulation. I have one section of the basement with dropped ceiling, so I need to worry about fire in that part. I was thinking about using the fire rated foam board with aluminum facing, but since there will be foam around the edges, drywall will probably be better.

[Bob10]

" insultating rim joists" I talk to mine in a polite manner right up until they give me trouble and then the insults fly

[EricU]

haha Bob, I didn't even notice that. I just switched to a wireless keyboard, and things ain't going in my favor. I used to use an IBM type M, so everything is a downgrade. I might have to get one of the modern type M keyboards with usb.

I try not to insultate anything like a water heater or a refrigerator that can get back at me. I'm hoping the rim joists can be big about it.

[Bob10]

watch your step