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

Extruded foam over slab

Eric Dopierala| Posted inEnergy Efficiency and Durabilityon

I have an existing pole barn that I’m converting to a workshop. Since this building will be heated I would like to insulate the existing slab which is pitched to middle so that it could be washed down back in the day. I will be putting down a layer of plastic with treated sleepers over it ripped from 1 1/2” at the end to 2 1/2” in the middle and then covered with plywood . If I use 1 1/2” XPS will the 1” air gap in the middle be inefficient? Am I better off having someone spray open cell spray foam that fills the void completely? Thank you.

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.

Replies

  1. Jon R||#1

    Consider leveling the floor with more concrete, omitting the sleepers, using epoxy as a vapor barrier and using EPS (possibly of higher than usual density). See below (figure 7) regarding epoxy vs plastic:

    https://buildingscience.com/documents/insights/bsi082-walking-the-plank

  2. Expert Member
    Dana Dorsett||#2

    What he said- the sleepers aren't necessary. Also consider using EPS rather than XPS, since the performance of XPS will eventually decline to that of EPS of similar density as it loses it's high global warming potential HFC blowing agents.

  3. Steve Knapp CZ 3A Georgia||#3

    Re Dana's comment. You might be able to source reclaimed EPS at quarter to a third the cost of new product. Check Craig's List and/or do a general browser search.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |