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Community and Q&A

Spray foam in crawl space under floor

AlexM | Posted in General Questions on

Can anyone share recommendations on how best to handle the following:

I just purchased a new (to me) cabin. It is in decent condition. Pocono Mountains, PA. It’s a single story on a crawl space – approx 4.5 ft high above a rat slab. Rat slab is in decent condition. Signs of some slight moisture around the perimeter. The walls have 2-3″ if closed cell spray foam on them. The floor and floor joist above the crawl space also have 2″ of spray foam on them (joists are flashed, joist bays are 2″).  The crawl space vents are still open, so it is a vented crawl space, but with insulated walls and insulated floor. There is no visible vapor barrier on the floor (maybe poly under the concrete, but not sure…).

So my questions are:

1. If there is no sign of mold or other problems, can I just leave this like this? Maybe just putting a small dehumidifer into the crawl space and letting it be, or 
2. Do I need to remove spray foam insulation from the floors and joists, close the vents, install a vapor barrier and a dehumidifer and make this a fully enclosed crawl space?

It seems like option 2 is the “right” way to do it… but I imagine removing closed cell foam is difficult/expensive, and am wondering if this is manageable as is?

p.s. I have no idea how long ago the install was done – it all looks good though – as in, not damaged or covered in mold or otherwise aged.

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  1. Expert Member
    Akos | | #1

    "If there is no sign of mold or other problems, can I just leave this like this"

    Since it is vented and in good shape I don't see why not.

    Sealed crawl would be more efficient but you have to now condition the crawlspace. This can be done many ways (dehumidifier, exhaust fan, transfer ducts) and might make the floor a bit warmer. If you do this, I would keep an eye on the crawl humidity to make sure the amount of conditioned air is sufficient to keep it about house levels. What you want to avoid is creating a space that is between indoors or outdoors, so when sealed it should be solidly part of the house. The spray foam on the floor joists doesn't need to be removed but it is redundant now.

    If it was my place, unless there is a good reason to change (say putting mechanicals down there), I would leave it as is.

    1. AlexM | | #3

      Can I just clarify - are you stating that if I did seal the crawlspace by closing the vents and then adding a dehumidifier, that I would be okay to leave the insulation on the underside of the floor?

      I assume this is fine so long as humidity levels are maintained in the crawlspace... but if they raised, then there would be a problem, right?

      1. Expert Member
        Akos | | #4

        Correct. As long as the crawl is conditioned and humidity is kept in check the insulation can stay. In the winter time you might need to put a small baseboard heater in there as well to keep it near (a bit bellow is fine) house temperature. Running this is no extra cost as the heat still stays within the house.

  2. AlexM | | #2

    Thanks, Akos. That's definitely the answer I was hoping to get... Although, truth be told, I am also looking at HVAC solutions as it currently just has baseboard electric - so there is a possibility I may want to hang an air handler and some duct work down in that space, complicating things a little.

    1. Expert Member
      Akos | | #5

      If you are on baseboard heat than a ducted heat pump in there would be an easy money saver if you can do it for a reasonable cost. Some of the DIY options (ie MrCool universal DIY), I would not be surprised the ROI would be a couple of years.

      One thing to watch when sealing a crawl is radon. Don't know if you have it in your area but if you have radon an exhaust fan or an ERV drawing stale air from the crawl might be needed.

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