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

Do You Need to Tape & Seam Seal XPS Over 6 Mil Poly in Basement?

cloves2016 | Posted in General Questions on

Hi everyone,

I had a question. I live in NJ zone 4. My basement is 4 feet underground and 4 feet above. I am doing an XPS reto install on the interior walls. I put down a 6 mil poly (5 inches up on all walls) and then 2 inches of XPS on the floor and lower walls. I have been using Dow Spray foam inbetween the wall of XPS and the XPS on the floor.

Do I need to seam seal all the joints using Tyvek tape (both wall and floor)? Or does the 6 mill poly below the floor eliminate the need to seam seal?

In the picture attached you can see the poly comig up from the floor. The black stuff is foundation coating (used to hold up the poly)

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

    You'll hear builders argue in favor of both sides of this question. If you have 6-mil poly under your rigid foam, you aren't going to get much air leakage through your floor assembly. But tape is relatively cheap, and many builders prefer to make their air barrier redundant.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |