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Community and Q&A

Crawl space spray foam in CZ 3c

Cousinmike | Posted in Energy Efficiency and Durability on

I’m currently undergoing a whole house renovation in the Bay Area, CA (CZ 3c) and have an existing vented crawl space to work with. I’d like to spray foam the subfloor (vs encapsulating the crawl space) but wanted some clarification around a couple options.

1) I had thought that closed cell was my only option here, but saw Dana’s reply (#2) in this Q&A:

Is using open cell a viable (and even preferred) option in my climate zone?

2) If going with closed cell, is encapsulating the entire floor joist with foam necessary in my CZ to prevent moisture-related issues in the subfloor, or can I get by with only spraying cc foam between the joists?


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  1. Expert Member
    BILL WICHERS | | #1

    Why do you want to insulate the subfloor instead of conditioning the crawlspace? It's usually easier to encapsulate and insulate the crawlspace, and that generally performs better too.


  2. Cousinmike | | #2

    Encapsulation is not commonly performed here so I’m not confident it would be done well. On the other hand, spray foaming the subfloor is something that should be relatively straightforward.

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