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Community and Q&A

Fixing a Wet Crawlspace

AlexD2022 | Posted in General Questions on

I’ll be taking possession of a house in Salem Oregon that has a substantial amount of water in the crawlspace – however no obvious signs of mold.

There are a few issues when I looked into the crawl (didn’t feel like spelunking down there so didn’t go through the whole space) and perimeter of the house. Mainly the vapor barrier is poorly laid and looks to be ~6 mil and there’s one corner of the house that is really poorly graded and looks to be directing water into the crawlspace via the air vents along with a downspout that is directing water right at the crawlspace entrance.

Obviously I need to fix the grade outside and maybe add some kind of well in front of the vents to make sure water doesn’t get in there. However is it a good idea to install an interior perimeter drain with a sump pump along with a new 15 mil vapor barrier? In my mind once water has gotten into the crawl you’ve already lost, however the bids I got for installing an interior drain system have been reasonable and I’m worried setting up an exterior system will be more expensive and much more disruptive even though I easily have the required slop on my property to daylight to the street. Additionally the interior drain could be set up now while to do an exterior drain everything would probably need to be hand dug since I don’t think the ground will dry out enough any time soon to get any kind of machinery to help with the digging.

Lastly, once I do fix the water issues, am I better off converting to a sealed crawl (I do have HVAC ducts in the crawl) or to keep it vented? I’ve read before on GBA that it’s not entirely clear how beneficial sealed crawlspaces are in the PNW.

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  1. walta100 | | #1

    If you are willing to trash the landscaping and spend the money an exterior drain to daylight is the perfect solution.
    The interior solution is OK until it rains when the electricity is out.

    It seems like the house has found a dry enough balance point to survive, seems like you should be OK if you can resist the temptation to change things like closing the vents, adding insulation or air sealing.

    A good machine operator can do amazing things. Try not to tell them how to do their job. If they say it is too wet listen, short of that let them make the call and do the work.


  2. Expert Member
    BILL WICHERS | | #2

    I would try to correct this as much as possible on the exterior, but I'd still put in an interior drain as some extra insurance while you're putting in the new liner. Think of the exterior gutters and grading as your main defensive measures, and the interior drain is the backup plan. Normally I wouldn't worry too much, but if you have a lot of standing water in your crawlspace already, then you have big problems.


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