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Spray foam on crawl space dirt?

user-4158387 | Posted in Energy, Heating & Insulation on December 11, 2014 11:32am

I have a crawl space that has spray foam between the floor joists and spray foam on the inside of the concrete walls and footer. It has plastic sheeting over the dirt.  All the vents are closed and I have put in a dehumidifier that drains to the outside.  The humidity stays around 40-45% and the temps are 63-68F.  I live in a very dry cold and hot climate, Wyoming at approx 5500 ft.  hot summers cold winters low temps -40, high temps 105F.

Has anyone ever tried spraying a crawlspace dirt floor with foam.  Seems to me it would seal the moisture out quite effectively, need no sealing of the plastic to the side walls and even make radon mitigation easier.

Since I have never hearedof it being done there must be a serious drawback, but other than price and a bit of fragility I can’t see why it would not work.

Any thoughts would be appreciated.

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Replies

  1. DanH | Dec 11, 2014 06:14pm | #1

    I think you'd have to quit calling it a "crawl" space.

  2. mark122 | Dec 11, 2014 11:32pm | #2

    spraying the ground is not something i have ever seen or heard of being done.

    I assume you have opend cell foam on the bottom side of your floor because closed cell will not allow the transefer of humidity the way that open cell does.

    Do you have a heat recovery system installed in the house?

  3. finefinish | Dec 13, 2014 02:47pm | #3

    Hi there, In cold climates dirt crawlspaces are usually just covered with heavy poly sealed to the insulated walls as you describe having.  This is all that is needed to control humidity in the crawlspace.  The temperature in a well insulated crawlspace like the one you have and the ground temperature within that space are probably quite close seasonally.  Your heat  inside the house during the winter should not be entering the crawlspace, not should your cool conditioned air enter the crawlspace in the summer.  Given that, it seems to me insulation at the dirt floor would be useless, like an insulated wall to separate 2 rooms that are perpetually 50*.  

  4. User avater
    deadnuts | Dec 13, 2014 08:30pm | #4

    not really

    user-4158387 wrote:

    Seems to me it would seal the moisture out quite effectively, need no sealing of the plastic to the side walls and even make radon mitigation easier.

    Any thoughts would be appreciated.

    Only if you spray closed cell icynene. However a heavy mill reinforced vapor barrier (10 mil+) will do it more effectivley and much more cost effectivley. The vapor barrier should lap up the concrete walls and the walls should be sprayed over it with open cell foam (reducing chance of wicking moisture to band areas).

    In our area, it is recommended that when the crawl space ground is isolated from moisture with a vapor barrier and the walls are insulated, that the main level floor is left uninsulated because you effectively have a conditioned crawl space that is somewhat conditioned (supply and return via air leakage) along with the rest of the home.You are conditioning the crawl space with a dehumidifier anyhow, why not nix that and let the home HVAC unit control this space as well?

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