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Community and Q&A

Slab on grade and plumbing penetrations

jhrockwell | Posted in Green Building Techniques on

I am looking for specific information about detailing plumbing waste lines for a slab on grade on Cape Ann (north of Boston, Zone 5A). I am concerned about sub-slab insulation, the air barrier, vapor barrier and general coordination of excavation, concrete and plumbing trades. I am familiar with Building Science Corporation’s recommendations for polyethylene location and “no fines” in the stone layer.

Thank you,
John Rockwell
Rockport, MA

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  1. davidmeiland | | #1

    Prior to the pour, tape the pipe penetrations to the plastic sheet, then put a piece of pipe insulation around each pipe that sticks up flush with top of slab. Later, if you want to, you can trim the pipe insulation below the slab a bit and replace with canned foam. There are a few useful details shown near the end of this document

  2. Jesse Thompson | | #2

    The 100K House folks used to have a very good page on using Stego wrap and how to seal penetrations, luckily the Google cache is still visible:

  3. spearrock | | #3

    I am wondering about this too. To bad those links are bad. Is there a newer thread with these informations?


  4. spearrock | | #4

    and how do you cut circular holes in XPS (or EPS) for plumbing penetrations?

    1. Expert Member
      BILL WICHERS | | #5

      I usually use a hole saw of the right size, and cut the hole by hand by twisting the hole saw back and forth. You can a reasonably clean hold this way, although there is usually some tearing. It's not important that the hole be perfect, so ends up working fine.

      Note that in XPS you can twist the hole back and forth. In EPS, which is more crumbly, it sometimes works better to twist the hole backwards only, opposite of how it would normally turn while using it in a drill. Going backwards makes it more gentle on the material, and you have less issues with tear out that way.


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