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

EPS rainscreen for walkout basement

Ithinkicanfixthat | Posted in General Questions on

Green builders,

I am planning on waterproofing the below-grade portion of my walkout basement. I plan to use a water based adhesive to apply a HDPE based waterproofing against the masonry blocks. Next, I will add 2” of rigid EPS. Lastly, I’ll finish off the below grade portions with a dimple board. For the above grade portions, I will create a rainscreen using furring strips and finish with cedar siding.

Is it OK to drill through the waterproofing membrane in order to attach furring strips to masonry walls on top of the EPS ? Will this potentially ruin the life of the HDPE membrane?

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


    If you are only fastening the rain-screen battens above grade to support siding:

    - Is there any advantage to extending the HDPE membrane high enough that the fasteners would penetrate it?

    - Why does it matter if the membrane is penetrated by the fasteners above grade?

    1. Ithinkicanfixthat | | #3

      Do you not recommend only extending the HDPE membrane above grade?

      I wanted to waterproof the masonry above grade to really remove moisture from the basement.

      1. Expert Member
        MALCOLM TAYLOR | | #4


        Above grade the foundation is protected from moisture by the rigid insulation, rain-screen gap and siding - just like framed walls above. None of them need a water-proof membrane on the outside.

  2. Expert Member
    BILL WICHERS | | #2

    If you’re really worried, squirt some silicone in the hole before inserting the fastener. The silicone will squish around as you tighten the fastener and help to seal the hole. I do this all the time on exterior masonry anchors to prevent water from getting in and freezing, then damaging, the masonry around the anchor.

    HDPE itself is pretty impervious and won’t be damaged by a fastener hole or any resulting leaks. The only worry might be that if you stress the HDPE sheet around the fastener you could potentially tear it, but it’s a tough material and should be pretty resistant to damage in normal situations.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |