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

Using XPS on basement wall with two different vertical surfaces

Smoke Teff | Posted in General Questions on

I’m finishing the basement of a row house in Philadelphia. The bottom 2/3 or so of my brick foundation is covered in parged concrete about 4″ thick. In other words, the vertical surface of the wall runs up from the floor to about 5′ in height, then there is a 4″ horizontal shelf leading to the brick foundation, which makes up the top 2′ of the wall. (The pictures should make this clear.)

I am planning to use XPS board to insulate the walls. Should I do anything to make the XPS against the brick flush with the XPS against the concrete? I was thinking I could stack two more layers of 2″ thick XPS against the brick, then run a single panel that should adhere flush to the concrete and the two extra layers of XPS on top. Or should I just adhere a single layer of XPS to all the surfaces (including a 4″ horizontal strip/shelf) on top of the parged concrete? This would leave an unfilled cavity behind the wood framing at the top of the wall.

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.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |