GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Reverse swimming pool crawlspace?

heartnhome | Posted in Energy Efficiency and Durability on

I have a 1960’s ranch with a full basement under 80% of the house.  The other 20% is over a crawlspace that’s connected to the full basement.  The crawlspace is known to take on 4″-6″ of water in heavy rain, and being coastal Rhode Island this isn’t uncommon (zone 5).  There’s no sump, but the water always disappears anyway and appears to be dry until the next storm.  The floor of the crawlspace is a rat slab right on top of dirt, so it seems that what doesn’t become vapor just gets absorbed back into the ground

I need to encapsulate the crawlspace and know that part of the water problem is most likely drainage from outside due to the slope of the yard.  Excavation and drainage from the outside is out of budget for now.

Does it make sense to air seal the rim joist with rigid foam, then lay poly on the floor/walls and tape the seams like crazy to keep the water under the poly, like a pool cover, until the exterior drainage can be taken care of?  Or will this cause other problems?

Thank you for any help – hope I got all the details in there.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Peter Engle | | #1

    Your approach might help to reduce the amount of dampness in the crawl/basement and probably won't cause any new damage. But I think you're missing the big point - it's really not good to have this much water entering the crawl space when it rains.
    You seem to already know the general reason but you might be ignoring some simple fixes. Clean your gutters, if you have them. Clogged gutters can dump tons of water against the foundations. Run your downspouts as far away from the house as you can. These two measures cost almost nothing and can fix 90% of interior water problems. Sometimes just a little bit of regrading can also help, and it is literally dirt cheap. If you have water ponding against the foundations when it rains, fill those areas with dirt and slope it away from the house. Even getting the water a couple of feet away from the foundations can make a big difference. Use clay-rich dirt, not topsoil. This can be a great DIY job. You can have a yard or two of dirt dumped in the driveway and move it yourself.
    Check the crawl vents. I've seen plenty of houses that have sunken areas around the vents that act like funnels to channel surface water into the crawl. If so, seal them up and fill the wells with dirt as above. You might be surprised how much of an effect you can have on crawl flooding with very simple and cheap interventions.

    1. heartnhome | | #3

      All makes sense - there are gutters, currently clear. Definitely can see if I can get them to direct water further away. I'll also have to look into the regrading.

      Thank you Peter!

    2. burninate | | #7

      Adding one note to this:

      A common problem in my area involves people digging holes in their low-water-permeable soil right up against the house so that the surface slopes towards the house, and then filling those holes with mulch and high-water-permeable garden soil (with a few bushes) to bring it up to grade. The water passes right through the mulch (it doesn't even "see it" from a grading perspective) and quickly through the garden soil and is then funneled against the foundation by the shape of the low-water-permeable subsoil.

      If you want an overview of how a novice might fix their crawlspace water problem by going all the way and putting in DIY drain tile, this was pretty thorough:

  2. Jon_R | | #2

    +1 on reducing the amount of water entering. If this doesn't do it, then consider adding a sump pump. In any case, keep the crawlspace dry (air exchange with a dehumidified basement will work).

    1. heartnhome | | #4

      Sump pump sounds like a great idea too. Luckily the full basement area is totally dry.

      Thanks Jon!

  3. Expert Member
    BILL WICHERS | | #5

    If your basement is dry but your crawlspace floods, that makes me think there is some “easy” way for water to get into your crawlspace. I’d look for that and fix it first. If it’s a dirt floor in the crawlspace, it would be terribly difficult to put in some drain tile and a sump to be sure the water doesn’t accumulate. You do NOT want standing water in there, and it’s a bigger deal once you’ve encapsulated the crawl space.


  4. walta100 | | #6

    I think you need to be very careful about what you do to your house. It seems your house has found a balance where whatever water is getting in is able to dry out and escape before mold can get growing and wood starts to rots.

    The word encapsulate is the language of huckster salesmen and is best avoided. The word implies that the crawl space is somehow separated from everything. Even if that were possible things could get moldy very fast as any moisture would have no way to escape.

    A crawlspace needs to be vented to the outdoors or conditioned and connected to the indoors space so it can dry to the indoors or the outdoors.

    If rain water is running toward your house you may need to move a lot of dirt divert the water away.

    DO NOT insulate or air seal anything until you find where the water is coming from and how to keep it out.


    1. Expert Member
      BILL WICHERS | | #8

      I agree about the crawlspace encapsulation. I have visions of the liner lifting up like a boat if water gets in ;-)

      Absolutely best to figure out where that water is coming from and fix that first. My thinking with a sump and some drain tile is for extra insurance just in case something gets missed somewhere.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |