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  1. #1
    Join Date
    Jun 2013
    Posts
    2

    Default Why is my crawlspace dirt moist?

    The dirt in my crawlspace is always damp (looks dark brown), even in the summer months. This is near Seattle.

    This in turn creates a musty odor which seeps into the living area.

    I need someone to help me figure out where the moisture comes from, so I can perhaps shut it down. There is a neighboring house that is several feet more elevated than my house. I wonder if the water run-off from their lawn could be the source of the problem.

    What kind of contractors can help me with this?

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    5,081

    Default Re: Why is my crawlspace dirt moist?

    Any general contractor can help you here.

    You got to find a way to reduce the humidity in the crawlspace: increase ventilation by using fans and adding vents.

    You can place a dehumidifier in there and see how much water it extracts every day.

    You can also place a 6mm moisture barrier plastic sheets on the ground.

  3. #3
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,359

    Default Re: Why is my crawlspace dirt moist?

    It may be that groundwater is a normal occurrence where you are. As DJ said, install a vapor barrier on the ground in the crawlspace. Make sure that foundation vents are kept open, especially in the winter. If your floors are not insulated, insulate them. In the Seattle area, you will have greater moisture problems in the winter than in the summer.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  4. #4
    Join Date
    Aug 2007
    Location
    Portland, Oregon, formerly of Chicago
    Posts
    1,583

    Default Re: Why is my crawlspace dirt moist?

    I live in the Portland, Oregon area with clay, volcanic soil and high water tables. Even with a crawlspace only a couple feet deep, it can be moist down there during the rainy season - Oct thru May . Vented crawl spaces are the norm here as temps are quite mild in winter. All the utility and water lines are down there.

    At a minimum, the earth should be totally covered with 6 mil plastic to keep the moisture trapped below. If you don't do this, no dehumidifier has a ghost of a chance of keeping up. Typically, the floor area is insulated to keep the house above foot warm.

    I don't really understand why this type of foundation treatment is so popular here. I am originally from Chicago where crawl spaces and deep basements are common. These areas are treated as part of the house envelope, if not outright heated, they are at least closed from the exterior. Again, utilities and water lines are down there so they have to be kept above freezing.

    Recently, many companies in the Portland area have been specializing in closing off the crawl spaces and encapulating the whole crawl space with 20 mil plastic. The vents are sealed shut , the walls insulated and even heat diverted into that space. At this point, insulation below floor is not neccessary. Where groundwater has been a problem, sump systems are installed. In effect, they are adopting the Mid-West type crawlspace.
    Last edited by ordjen; 09-28-2013 at 03:28 PM.

  5. #5
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,359

    Default Re: Why is my crawlspace dirt moist?

    Quote Originally Posted by ordjen View Post
    I don't really understand why this type of foundation treatment is so popular here. I am originally from Chicago where crawl spaces and deep basements are common. These areas are treated as part of the house envelope, if not outright heated, they are at least closed from the exterior. Again, utilities and water lines are down there so they have to be kept above freezing.
    In the midwest, you are more likely to see basements even in modest homes due to the fact that utility lines (water, sewer) must be buried at least 6 feet deep and also due to the severe winters. When it's 30 below, it's easier to keep the house warm with a basement than with a vented crawlspace. Besides, the water meter needs to be indoors for the same reason: extreme winters.

    In temperate regions such as the Pacific Northwest, a vented crawlspace is more common because it's a lot cheaper than a full basement, a full basement isn't necessary for protection of utilities (18" is standard depth for frost protection), and energy bills will be higher with a full basement because of the increased space that must be heated and cooled. Besides, groundwater tends to be a greater problem here than in the midwest; keeping the basement dry in the rainy season is a lot harder to do than in the midwest. But the main reason you see vented crawlspaces is because it's cheaper.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

  6. #6
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,360

    Default Re: Why is my crawlspace dirt moist?

    What they said about the sheet plastic under ceement plus;

    with our very high water table and not-uncommon flooding there are no basements in my fair city.

  7. #7
    Join Date
    Aug 2007
    Location
    Portland, Oregon, formerly of Chicago
    Posts
    1,583

    Default Re: Why is my crawlspace dirt moist?

    Fencepost,

    I am sure you are correct about cost being the determinent, but if I were custom re-building this house, I would suffer the extra expense and make it a little deeper and enclose the area into the house envelope. Code calls for a minimum 24inch space, but when air ducts etc. are in the way, you really do a belly crawl to get around down there!

    The oher thing I never saw in the Mid-West is the floor construction. Back there a floor would have 2x joists with 3/4 inch subfloor and flooring on it. Usually a steel I Beam would go down the middle of the basement. This house has 4x8 joists with 1 1/2 tongue and groove subflooring which is supported by 24 piers and posts. I must admit it is solid! But then, Oregon is wood country!

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