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Community and Q&A

Insulating a crawl space

Greg Smith | Posted in Energy Efficiency and Durability on

Situation: Existing uninsulated very shallow crawl space with a concrete floor that doesn’t have insulation or vapor barrier under the slab located in climate zone 6 just a few miles south of the “border” for climate zone 7.

My plan is to insulate the space with 4″ on the walls and 2″ on the slab of type 1 EPS and then cover that with about as much blown cellulose as I can fit in the space (about 2′ high). It is empty space – no mechanicals of any sort in there.

Does it make sense to seal it up once it’s insulated? Or because of the climate zone would insulating the wood floor and then venting the space be more appropriate?

Should there be a vapor barrier on top of the slab and under the EPS in either case?

Or is there a better all around option for insulating the space?


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  1. GBA Editor
    Martin Holladay | | #1

    I don't recommend using cellulose in a crawl space. Crawl spaces tend to be damp. The only insulation products that make sense for crawl spaces are foam insulations: either sprayed polyurethane foam or rigid foam. EPS is fine.

    I would advise you to stick with rigid foam. If you want to increase the R-value, just add thicker foam.

    For more information, see Building an Unvented Crawl Space.

  2. Greg Smith | | #2

    Thanks Martin.

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