08:21AM | 11/14/02
Member Since: 09/27/02
3 lifetime posts
We are putting a 300 sq ft addition on our house in northern Virginia. There is a crawl space under the new addition. Since the addition increases the size of our kitchen and adds a laundry room, we also have HVAC ducts and pipes running through it.

The builders vented the crawlspace as required by County code. But I am looking into issues of mold, moisture, etc. and have found multiple ways to deal with these. One is to open the vents in winter and close them in summer. Sounds OK for moisture, but not so hot for keeping the temperature of my pipes above freezing (though I did have them wrap heat tape around them) and keeping the floor warm.

Another approach is to insulate the crawlspace and run the HVAC into it, making it into sort of a mini-basement. Since it's only 300 sq feet and under 3 ft high throughout, I figure this would not be too much of a strain on my furnace and air conditioning.

I also found something called a Smart Vent ( which is a powered vent that comes on only when the temperature is above 43 degrees and there is less moisture in the outside air than in the inside air. The theory is that the air entering the crawlspace will then always be dryer than the air inside it, and it will thus be dried out.

Does anyone have any experience or knowledge of any of these approaches? My wife is worried about mold growing in there, so I want to feel pretty good about how we deal with it.


06:29AM | 11/15/02
Member Since: 03/13/00
1678 lifetime posts
Assuming the bottom surface will be dirt or gravel, I strongly recommend a layer of plastic. It will greatly reduce the moisture level in the crawl space. It made a huge difference in mine.
As to the moist air that comes in through the vents, I leave my vents closed all year.


11:25AM | 11/15/02
Member Since: 06/03/01
327 lifetime posts
Think you may have the thought backwards. Normally, you would close the vents in winter and open in summer when relative humidity is worse. By all means, use the plastic and cover with stones to keep it in place.


10:06AM | 04/03/13
Here's a site with more information


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