Sealing plumbing vent through foam insulation
dfvellone
| Posted in General Questions on
Installing a 2″ plumbing vent through 2nd floor ceiling ccsf insulation, and I’m wondering if I should cut an oversized hole and then seal with canned foam, or cut a snug hole and seal with caulk. My concern is regarding what will best offer a seal that might resist any movement and retain its integrity over time.
Thank you, Daniel
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Replies
I would use an oversized hole and canned foam. If you're worried about movement, use the "Door and Window" type of canned foam that stays a little soft after curing.
Note that a hole saw on a drill will make a nice, clean hole in spray foam. If you need to go through a thick layer, use the hole saw first, then break off the "plug", and insert the hole saw to go deeper. This will give you a much cleaner hole than if you try to cut the hole by hand using any kind of handsaw.
I would try to cut the hole oversize enough to allow about a 1/4" to 3/8" gap all the way around the pipe, then fill the gap with canned foam until it oozes out a little when it cures. Note that canned foam won't cure properly in very thick layers, so if you have to go through more than about 2" or so of spray foam, I would add canned foam to about 1.5-2" thick, wait for it to cure, then add another layer, building up that way until you completely fill the hole. If you try to do the entire thick layer all at once, the inner part of the canned foam tends not to cure well so you end up with voids.
Bill