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

What is the best practice and material to insulate my crawspace ceiling?

redeft | Posted in Energy Efficiency and Durability on

I own a 22’X32′ ranch home(vacation property) in upstate New York. I had the crawlspace “encapsulated” last year which took care of the bulk of the moisture problems. I’m left with fiberglass batts in the ceiling(floor of the living space) that are starting to fall and make a general mess of the space. Is closed cell spray foam a good option to fix this problem? What other issues might I encounter? What about rodents? They try to move in every fall, but I’ve been able to keep them at bay with prudent use of traps. A little more, my oil storage tank is located in the crawlspace but the boiler and other utilities are in a separate room on the main floor. What if any are issues with allowing air flow in and out of the crawlspace?
Any and all answers are greatly appreciated.

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. wjrobinson | | #1

    Call Doug at Northeast Sprayfoam.

  2. GBA Editor
    Martin Holladay | | #2

    First, read this article: Building an Unvented Crawl Space.

    The best approach is to insulate the crawl space walls and make sure the crawl space isn't vented.

    If you want to insulate the crawl space ceiling, remove and throw away the fiberglass batts, and insulate under the floor joists with a continuous layer of 2-inch-thick polyisocyanurate.

  3. Expert Member
    ARMANDO COBO | | #3

    If you have ducts or pipes in a well sealed and unvented crawl space, I usually prefer to insulate the perimeter wall with rigid foam and spray foam around the rim joist; that helps keep pipes and ducts warm. Don’t forget to provide ventilation for that crawl space.

  4. GBA Editor
    Martin Holladay | | #4

    Your advice is confusing. Are you advocating in favor of sealed crawl spaces or ventilated crawl spaces?

    My own preference is for sealed crawl spaces.

  5. redeft | | #5

    Martin, Thank you for the prompt reply.
    So a little more information- The walls have Silver Glo® Insulation Panels, glued and screwed, then there is a 20 mil poly reinforced vapor barrier on the floor to about 12" up the wall. My incoming water line is insulated as it is from a well and always cool, I plan to insulate the waste line from the bathroom also. There are four windows in the crawlspace(Anderson® Basement Windows) which I plan to seal shut after reading your article. I also am planning on adding two floor registers at either end for passive ventilation of conditioned air.
    Is the spray foam a good idea or should I go with rigid foam board? My guess would be that the rigid foam board would be cheaper and I can install it myself.

    Thanks again

  6. GBA Editor
    Martin Holladay | | #6

    I'm not familiar with SilverGlo insulation. It's hard to tell from the website whether it is a true R-11 foam (in other words, a product that is 1.5 to 2 inches thick) or whether it is a thin product with a radiant barrier and an inflated R-value claim.

    If you already have 1.5 to 2 inches of rigid foam insulation on your crawl space wall, you may not need additional insulation. However, if you want to boost the insulation R-value, more rigid foam or spray foam can always be added. Be sure to check on local building codes to find out whether the foam needs to be protected with a thermal barrier like drywall.

    In addition to installing at least one floor register to connect the conditioned space above with the crawl space below, you also need to install either an exhaust fan in the rim joist or a supply duct in the crawl space connected to your forced-air heating and cooling system. More information on these details can be found in the article I linked to.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |