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

No clear sign of mold after 33 years, so okay to again use batt and vapor barrier in basement? Batts started 2′ above floor. Can I batt all the way down?

Melville2 | Posted in General Questions on
I would do spray foam, but I can’t get an installer for 3 weeks, and tenant can’t wait.
Brick wall, no significant signs of water issues.  I know polyethylene vapor barriers should not be used in basements because moisture will be trapped.  I know batts without poly should not be used in basements because humidity will condense on the cold surface of the brick, resulting in perhaps-puddles on the concrete [sub]-floor.  I know spray foam is recommended on a basement brick wall if there are no water penetration issues and if the brick is not likely to get much water exposure and if the brick is strong enough to not be damaged by freeze and thaw cycles.
After a flood led me to eventually completely open the walls, I felt good getting rid of the old batts, and some of the pink fiberglass was dark, but I’m guessing with dust not mold.
No clear sign of mold after 33 years, so okay to again use batt (this time rockwool?) and vapor barrier in basement? Batts started 2′ above floor – meaning heat/cold flowed thru the drywall and cracks, thru the air gap next to the exterior double-brick wall. Can I batt all the way down?  (to the top of the wooden wall framing bottom plate)

Toronto, climate zone 5a



  1. Melville2 | | #1

    I said that I guessed the darker areas on the pink insulation were dirt, not mold. It wasn't just a random guess. I did consult articles like "How to Tell if Insulation Is Dirty or Moldy"
    ( and "Mold on Insulation" (

    I lived in the house for 20 years and I never experienced symptoms like allergies. Nor has any tenant since the basement began being rented 10 years ago. The 1st floor tenants have been here 7 years - no complaints.

  2. Expert Member


    The advice given on GBA generally falls into the category of: If you do this you won't have any problems. It doesn't follow from that that assemblies which are risky will necessarily fail, just that you can't be surprised if they do.

    I suspect your walls will continue to be fine if you replace what was there with a similar assembly (that is batts for batts, and I don't see much of a problem with extending them down to the floor). But adding poly, if there was none there before, might be what tips it into having mold problems.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |