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Vented crawl space insulation, Southern California

Mike Simanyi| Posted inEnergy Efficiency and Durabilityon

I’m in the early stages of rebuilding my house, which happens to have a ventilated crawl space. I believe I’m in climate zone 3B, and my project manager is encouraging me to simply use fiberglass batt between the floor joists to achieve the required R-13 insulation.

When I suggested a combination of that as well as rigid foam beneath the joists (per figure 7 here:http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces?topic=resources/cond-crawlspaces), he discussed it with the insulation contractor. Apparently there is a fire code issue with that particular configuration.

Can anyone suggest “best practices” for my situation. I’ve read a great deal in the past couple months, but still feel quite uneducated on the subject. I’m sure I’ll be discussing this with the insulation contractor soon, so any suggestions are appreciated.

Mike

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Replies

  1. GBA Editor
    Martin Holladay||#1

    Mike,
    In some jurisdictions, local code officials insist that rigid foam be protected by a layer of 1/2-inch drywall. That is one option. (Of course, you should check with your local code official before proceeding.)

    You might also specify Thermax, a brand of polyisocyanurate insulation that has a facing that has passed fire testing and is usually accepted in this application without the need to install drywall.

    The third option is to create an unvented conditioned crawl space. For more information on this option, seeBuilding an Unvented Crawl Space.

  2. Expert Member
    Dana Dorsett||#2

    In crawlspaces it's often less foam to insulate the foundation walls rather than the bottoms of the joists.

    It's easier to reliably air seal the foundation walls than the sub-floor too.

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