When I bought my house, the termite inspector found some damage to a 4 foot section of rim joist. The seller hired a crappy termite contractor to remedy. They shot a length of 2×8 over the rotten section and filled the gap with cement. There are a couple of penetrations for NM cable and an external gas hookup in that section, and they notched the new board so as not to have to disturb them. Last winter that whole area was unbelievably drafty–wind literally blowing directly in. I used spray foam all around and behind the new board. I drilled a few 1/4″ holes in the new board, stuck the foam nozzle in one of them and it took quite a bit of foam before I saw any ooze out of other holes. The draft in the basement is gone but the wall and floor above are still cold and drafty. The wall is uninsulated. Outside the house is vinyl siding over the previous exterior, the bottom edge of which looks like some kind of wood shingles. So finally, my question: Assuming the nozzle fits, would it be OK to spray some foam behind the wood shingles in the problem area? I’d basically be trying to hit the rim joist near those penetrations, but from the outside. The reason I hesitate is I wouldn’t want to create a trap for moisture, but I think the risk of that might be less than the cost of having a hole in your house that is invisible to all but cold air and insects. Love to get everyone’s thoughts on the matter.
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Sorry Eldon, missing info, there is no basement?, your rim joist sits on piers, full foundation, crawl space?, no access from inside?, or are you talking about insulating the floor, wall ??
wane, I think the attached image will explain. I haven't exactly confirmed the balloon framing but it's the only thing that makes sense.
I think I understand now, but not sure why you wouldn't drill from the inside to spray if it is built this way. However, usually the wall is built on top of the subfloor, which sits on top of the rim joists, not the mud sill as you diag illustrates. More than likely the whole wall is poorly insulated so doing behind the rim joist wouldn't help much. You could always remove a baseboard and cut a hole in the drywall, or just call an insulation contractor who can insulate the entire wall. Insulation is a gift that keeps on giving!
I believe this type of framing is called balloon framing. The house is circa 1930. The walls are plaster & wood lath. I think all the first floor walls are uninsulated. Someday I'll get to that but I thought that maybe applying foam behind the bottom edge of the sheathing might seal gaps that allow cold air into the wall cavity. It's something that would take 5 minutes to do; it might help or it might not. I just want to know if it will hurt anything. I could drill into each stud bay through the rim joist from inside but that would take a lot more than a couple cans of foam. I'd rather get the whole wall insulated.
You won't hurt anything using
You won't hurt anything using the spray foam as you have been IF your siding is shedding water properly.
Best I can suggest is look the area over after some heavy weather and if it is dry then there should be no problem with the spray foam.
I really would take the advice and get a professional to insulate the entire wall. Your method is hit or miss at best.
Terry