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

How would you insulate this overhang?

Poot_Klopp | Posted in Green Building Techniques on


I’m planning on updating the insulation and air sealing this section of my home. Would you just follow the guidelines for cantilever flooring outlined below? The only reason I ask is the distance of my overhang vs what is shown in the article.

Thanks in advance!

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
  2. Poot_Klopp | | #2

    Thanks Malcolm, any chance you provide some insight into the difference between the two assemblies? Specifically, do you know why there is no need for rigid foam on the sub floor in your linked article?

    Also the first line in the article specifically mentions overhangs under 24". Any insight on that?

    1. Expert Member
      MALCOLM TAYLOR | | #3


      In the article I linked to they used Zip-R sheathing rather than rigid foam on its own. I don't think it matters much which you choose.

      The 24" refers to the typical code maximum for cantilevers. After that you usually end up with a floor supported by piers and beams. The insulation is very similar though.

      From bottom to top the layers are:
      - A protective cladding to stop pests.
      - A layer of rigid foam to reduce thermal bridging.
      - Cavity insulation - batt or blown. A sealed sub- floor.
      - (Ideally) a permeable floor covering.
      The more of the layers you air-seal the better.

  3. Poot_Klopp | | #4

    Malcolm, that all makes sense. Unfortunately the previous owners installed what I think is some kind of vinyl flooring. I need to find the exact product details. It is also installed over what like like 2-3 other layers of older flooring or sub flooring. I have seen that vinyl is not ideal in other articles. Are there any alternative solutions if it is vinyl? Or would the same setup be used?

    1. Expert Member
      MALCOLM TAYLOR | | #5


      It's not a big problem - especially when it is that high above grade. That's why I added "ideally".

  4. Poot_Klopp | | #6

    One other consideration. The far end of the joists connect/are open to my unfinished basement as shown in the picture here (you can see the old batts and some foam the old owners stuffed in).

    Should I block and seal as per the articles? Or would there be any benefit to leaving it open? The basement is "semi" conditioned. But has no insulation on the interior walls. The basement is getting air sealed and the rim joist foamed if that matters.

    1. Expert Member
      MALCOLM TAYLOR | | #7

      Definitely block off the joist bays at the exterior walls and air-seal.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |