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

How to seal and insulate a crawl space in a humid environment

Colleen Bruning-Fann | Posted in General Questions on

We purchased a second home on a lake in mid-Michigan in Winter. With Summer, we discovered a moisture problem in the very narrow (16″ deep) crawl space. The previous owner had put 6″ fiberglass batts under the floor to insulate the crawl space and used plastic film as a vapor barrier over some of the ground. When we crawled through this narrow crawl space, we discovered the fiberglass batts were wet and falling into the crawl space, mold was forming on the floor joists, and there was water puddling on the vapor barrier covering the ground. The house rests on a foundation of pressure treated posts with pressure treated wood forming a barrier to keep animals out of the crawl space. It doesn’t seem possible to condition the crawl space due to air leakage through the boards.

We would like to remedy the moisture problem and insulate the crawl space but aren’t sure what to do.

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

    The correct approach is to excavate soil from your crawl space to improve access.

    Once this is done, you can either:

    1. Install new insulation in the joist bays (following the advice in this article: How to Insulate a Cold Floor) and remove the crawl space walls so that the wind flows freely under your house.

    2. Pour new concrete stem walls and create an unvented conditioned crawl space as explained in this article: Building an Unvented Crawl Space.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |