ventilating crawl space
Is the crawlspace completely separate from the rest of the house?
Is it dirt or poured concrete?
Is it vented to the outside?
Is it heated?
What room is over the top?
What part of the country do you live in?
Jay J -Moderator
PS: God Bless America!
If the moisture problem is UNDER the plastic, there shouldn't be any problems. If water is on TOP of the plastic, then you do have a problem. Either way, first, make sure the plastic is 6 mil thick and held down on the edges with gravel or Pressure Treated lumber. Water on top means that water is 'running', or 'dripping', onto it. The source is from the outside; not the crawlspace floor. You mentioned that there have been water-related problems in the past in the crawl. Well, one needs to do an assessment of the 'situation' OUTSIDE of the crawl before any work is done.
During the next rainstorm, don a raincoat, boots, and an umbrella (keeping an eye out for lightening!) As the rain comes down, watch where the water is running off of the roof. Is it running over or 'behind' the gutters? Is it running out of 'seams' in the gutter where 2 gutter-pieces meet? Is the water in the downspout leaking anywhere? Is the water that runs out the downspout running BACK towards the foundation? Is water running off of a roof line where there needs to be a gutter? Is there any pooling of water near the foundation? Does a neighbor's water, or water from another part of your lot, run back towards the foundation? If the answer is yes to ANY of these questions, then fixes need to be made.
(Hang in there w/me ...) Over 90% of the causes of water in a crawl are due to problems associated w/the 'things' I mentioned just a moment ago. Fixing them may alleviate enough of your problem that the water will stop entering the crawl (except, perhaps, in a 100 year storm.)
Regarding the power vent - I don't recommend it. All this would do is draw warm, moist air from outside and 'dump' it into a cool, dry crawlspace. As you know, warm air holds MORE moisture than cool air. So, if you were to do what you're being advised to do, the moisture will condense-out of the air and on to your joists, and on TOP of your plastic, thus, creating a mold/mildew problem. Drawing in air under power will compound this effect a great deal whereas under 'natural conditions', you don't even see it occurring.
Also, the floor above the crawl should be insulated. I know Virginia does experience a Winter season. The insulation should be R-30, or better, with the Kraft side facing the UNDERSIDE of the heated floor. (The Kraft is a vapor barrier.) DON'T go nailing up any plastic onto the bottom of the joists. This will only trap moisture. And to boot, if your floor is cold in the Winter, consider laying Insulation Board (that you would custom cut out) over top of your vent opening (from the outside.) You can use whatever you want to keep them in place for Winter. And when Summer comes, you remove them to vent the crawl. The Board I'm referring to can be bought at any Home Center. It's 2" thick ...
Once you take a look at the water drainage and its 'movement' around the foundation, and fix any problems listed above, you should be in a better position to evaluate if you still have a problem. I believe this will make the need for a power vent moot. Again, IMO, a power vent is a bad move. My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!
[This message has been edited by Jay J (edited November 27, 2001).]
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