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Should I lay out EPS insulation on my crawl space floor?

Dysd | Posted in General Questions on

First let me start by saying thank you for taking time out to answer my questions. I know there has been a lot of discussions on crawl spaces.
I purchased a home in need of some exterior rehab, the crawl space is my main concern, I want to turn it in to a conditioned space. I have moisture there but I am not sure if once I am done putting down spouts on the gutters, cleaning gutters, and correcting the furnace condensation line from discharging in to the crawl space plus re-hooking up the separated flex vent how much moisture will be there due to the negative slope around the house.
My budget is limited i was considering putting down 45 mil epdm over the gravel then 2″ eps over the epdm and on the walls. The materials listed are free for me, I also considered nailing fan foil to the uninsulated floor joist.

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  1. GBA Editor
    Martin Holladay | | #1

    In case you haven't seen it yet, I'll point out that there is a GBA article on the topic. Here is the link: Building an Unvented Crawl Space.

    You forgot to tell us your geographical location or climate zone.

    I'm not sure what you mean by "the negative slope around the house." If you mean that the exterior grade slopes toward your house rather than away from your house, that's a big problem, especially in a case (like yours) where the existing crawl space is damp. Ideally, you would excavate the soil around your house so that the grade slopes away from the house on all four sides. This can be done by creating a swale on the uphill side.

    Usually, it's best to wait after this work is complete to confirm that the crawl space is dry before proceeding with insulation work.

    Once your crawl space is dry, you can proceed with the plan to install a vapor barrier and insulation. If the EPS is free, there is no reason not to install it on the floor. I advise you to lay down a strip of OSB from one side of the crawl space to the other, on top of the EPS, as a catwalk for access (for maintenance workers).

  2. user-1072251 | | #2

    The EPS should be installed on the stone, with the poly on top of that. Tape the joints, tape the poly to the wall foam. or to the foundation wall if there is no wall foam.

  3. Dysd | | #3

    Thanks for your response, I was given enough EPS to also cover the walls, if I understand everything I have been reading (probably over reading lol) I should stop the eps and poly before it is even with the rim joist? I wasn't going to use poly because everyone mentions 10 or 20 ml poly and that is out of my price range, a friend of mine gave me black 45 ml epdm along with the eps to use a the vapour barrier. I know the epdm has a higher permeance than the ploy but I was hoping it would be suitable for a crawl space. Thanks in advance for everyone's assistance.

  4. GBA Editor
    Martin Holladay | | #4

    The EPDM will work fine.

    In addition to insulating your walls, it's also a good idea to install insulation at the rim joist area. Here is a link to an article the explains what you need to do: Insulating rim joists.

  5. Dysd | | #5

    Thank you all for your feedback, I am working under there today removing all the old hvac equipment and old duct work. The previous owner had new hvac installed in the house but left all the old equipment in the crawl last question any suggestion on what to use to tape the epdm to the eps? I know eps is sensitive to adhesives. Thanks again everyone sites like this are invaluable.

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