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Old 03-04-2012, 02:44 AM   #1
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Crawlspace perimeter drain and sump pump needed?


I've read numerous articles about crawlspace moisture issues and solutions online but can't seem to find an answer to a drainage question. I have a central NC crawlspace that is musty, lightly moldy and the odors are coming into the main level of the house. Last year, I installed a 6mil vapor barrier over 100% of the floor and up the walls. I also put in a portable dehumidifier and created an underground gutter downspout system to get water away from my foundation. Current grading is good on all sides except the front of the house which is level. (No way to change this without a huge expense) The odors have lessened and the crawl space is better than years past. However, I still have the mustiness odor coming in the space and I am thinking of redoing the project with a thicker liner, better seals, etc and insulate the walls, remove old floor R-19 insulation (condition the area) and perhaps add a perimeter drain to help dry out the ground. I don't have much in the way of ponding, but there are a few very small areas (6" x 6" or so) of water under the vapor barrier and the rest you can see droplets of moisture on the underside as well. It is doing its job but I was thinking of putting in a perimeter drain which will be a lot of work for one person. Is this overkill and usually reserved for homes with more standing water, after a rainfall or will this drastically dry the ground out and reduce the moisture levels within the crawl even with minimal if no standing water? Thanks

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Old 03-04-2012, 07:35 AM   #2
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Crawlspace perimeter drain and sump pump needed?


Is it water vapor or water that you are dealing with?

If it is water vapor, then the footing drain will not be the solution. If it is water vapor, condensation may be forming on the bottom surface of the vapor barrier. It would do this if the vapor barrier was at the dew point temperature. If this is the problem, try keeping your vapor barrier at a temperature above the dew point temperature. (Perhaps by insulating on top of your vapor barrier, etc.)

If it is subterranean water, the drain will help. You could dig a few 6 inch diameter holes in the floor of the crawlspace, a foot deep or so, and see if they fill up with water in a day or two. If so, you probably need a footing drain.

Regarding the dehumidifer: What is the relative humidity in the crawlspace? (Perhaps you own one of those inexpensive humidity measuring tools like one you can get at Grainger, etc.) The dehumidifer will not remove moisture from below the vapor barrier.

I had an interesting basement seepage problem years ago. My new house needed to have a perimeter under-floor footing drain retro-fitted after we had moved in due to seepage. Years later, when the next row of new houses were built, they discovered the presence of an old farmers field drain tile that had been cut during the construction of the new house. They blocked that drain tile,and it eliminated the seepage to my house.

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