GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

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

etting | 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?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member


    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. etting | | #2

      Extremely helpful, Malcolm; thank you!

  2. andy_ | | #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. etting | | #4

    Thank you, Andy.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |