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Sealing Penetration of Plumbing Vent Stack Through Closed-Cell Spray Foam

dfvellone | Posted in General Questions on

I’ll soon be installing my main vent stack for my plumbing drains. The penetration through the second floor ceiling will be through closed cell foam. Is the sealing detail as simple as using canned foam to seal off the penetration?
Thanks, Daniel

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  1. Expert Member
    BILL WICHERS | | #1

    Canned foam will work fine for this. You can cut the spray foam with a hole saw, just cut the hole about 1ā€ larger diameter than the outside diameter of the vent pipe. This will leave about a 1/2ā€ gap all the way around the vent pipe that is easy to fill with canned foam. I would use one of the better grades of canned foam in this particular application too, I like loctite tite foam, my spray foam contractor likes the OSI quad foam in the black cans that fit the foam guns. Both are better than the usual great stuff material since they are denser and closer in consistency to the two part spray foam.

    Iā€™m assuming here that this is just an interior air seal and not a roof penetration. Going through the roof would also need the weather boot and associated flashing above the roof sheathing (assuming the typical shingle roof).


    1. dfvellone | | #2

      It is the interior penetration: through the second floor ceiling insulation into the unheated attic. From there, of course, the vent runs through the roof where a boot and flashing will be provided.

      I'm not familiar with that canned foam, having used Great Stuff Pro. Is it superior to Great Stuff Pro? I have noticed that Great Suff Pro's density is noticeably less than the commercially installed ccsf.

      1. Expert Member
        BILL WICHERS | | #3

        Great stuff is "one part" foam. It will never be as dense as the "two part" commerical stuff that the spray foam contractors install. Loctite's "Tite Foam" is MUCH denser (and also 2-3x more expensive) than great stuff, but I like to use it for more critical applicaitons where I think stuff might get mechanically stressed occasionally. This means I use it for putting rigid foam panels up in rim joist areas, and pipe penetrations where I think the pipe might expand/contract a bit with temperature changes. I look at the better grade of canned foam as cheap insurance.

        The OSI foam is used by my spray foam contractor to fill in small voids they find in their spray foam applications after they're done spraying. It looks about the same after curing, but it's not quite as dense, either.

        Great stuff is a good product, but as with anything else there are places where it's a good fit and other places where different products will often work better. I use great stuff (in the gun) for "normal" air sealing (holes around wires, gaps between boards, etc.), and I use the more expensive tite foam for rim joist panels where the canned foam is also supporting the rigid foam panel, and larger pipe penetrations. I have also found out the tite foam product holds up better outdoors over time, but it does degrade so it's best to protect it with something -- even if that "something" is just a heavy coat of paint.

        You can get Loctite Tite Foam in the box stores. It's usually right next to the Great Stuf, but it's in a smaller can for about double the price. They recently changed it from a mostly blue to a mostly red can too. The OSI stuff is in a black can and I haven't used it myself, but my spray foam contractor buys it by the case.


        1. dfvellone | | #4

          Thanks for this info. It's really helpful and I appreciate it.

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