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Optimal size holes for drain and vent pipes through non-bearing bottom and top plates?

Jeff Cooper | Posted in General Questions on

What size holes would you recommend drilling to run 1-1/2″ABS vent pipes through the top plates and 2″ ABS drain pipes through the bottom plates of interior, non-loadbearing 2×4 walls so that they have a bit of room for expansion/contraction and they can be air-sealed with caulk or spray foam?  I expect the answer may depend on which material will be used for sealing; which is better?

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Jeff,

    I've always used a 2" hole saw for 1 1/2" abs and 2 1/2" for the 2". That gives you a pretty snug fit with about an 1/8" gap. I use a flexible caulk like Big Stretch to seal them.

    Both are large en0ugh that they need protection plates in a 2"x4" wall.

    1. Jeff Cooper | | #2

      Extremely helpful, Malcolm; thank you!

  2. Andy S | | #3

    1/8-1/4" gap is usually what I see on new builds. Don't know if it's a real reason, or one of those "that's just what we've always done" excuses, but I've been told it helps reduce squeaks when the pipes expand and contract from heat.
    Fireblocking caulk or foam is required here for all those penetrations. Probably required where you are too.

  3. Jeff Cooper | | #4

    Thank you, Andy.

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