GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

Use scrap polyiso for inground gutters?

agurkas | Posted in GBA Pro Help on

I have bunch of scrap 1 1/2″ fiberglass-faced roofing polyiso left over from basement insulation project. Next large project I will be working on is fixing grading issues around the perimeter of the house, removing all the bushes right next to foundation, and putting down washed p-stone (likely). I have read before on GBA about those inground insulation “skirts”, but there XPS or EPS is recommended with EPDM on top. Would it be bad to just use scrap polyiso under EPDM?

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. GBA Editor
    Martin Holladay | | #1

    If you already own the polyiso, I would go ahead with your plan. The price is right.

  2. Expert Member
    Dana Dorsett | | #2

    The price may be right, but the material is wrong. Unlike EPS and XPS, polyiso is hygroscopic- it can and will wick up water and hang onto it when buried. It's effectiveness as insulation falls very dramatically when that happens.

    Given the amount of labor involved in that project it's probably worth buying some EPS instead.

  3. charlie_sullivan | | #3

    It's a tough call whether to go with Dana's advice or Martin's. To me, it depends on whether your main purpose is water diversion or insulation. If the main purpose is water diversion, and throwing some insulation in while you have it dug out is just a bonus, it can't hurt. But if you are counting on getting some R-value for your effort, EPS is not very expensive and will be much more reliable underground insulation.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |