Crawlspace Ventilation?


Old 07-01-15, 06:35 AM
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Crawlspace Ventilation?

I live in Alabama and have a large, tall crawlspace in about 3/4 of my home with 1/4 unfinished basement.
I use a dehumidifier in the basement and was just wondering if I should leave the crawlspace vents closed or open?
Crawlspace smells a little musky closed or open, and I have a lot of items stored there.
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Old 07-01-15, 07:05 AM
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Most newer homes have crawl space vents that can be opened and closed. I leave mine open in summer and only close them during the coldest winter months. And... crawl spaces always smell musty. Storing items in a crawl space is risky unless they are in airtight plastic containers.
Old 07-13-15, 07:44 AM
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When you put in a dehumidifier, you want to seal the crawl space. Otherwise the hot wet air will continue to come into the crawl space. I added one 2 weeks ago and the humidity went down from 89% to 50%.. it is so dry after only a week. Even the cement walls are drying. I read various articles that as well as closing the vents, also added some foam to seal them.
Old 07-13-15, 07:54 AM
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If your outside summer air is hot humid it will carry a lot of moisture. The irony for vents when dealing with moisture is they should be closed in the summer and open in the winter, but that is difficult when dealing with temperature.

The other option with a crawlspace is to permanently seal it and condition that space. This approach eliminates that musty smell, which is probably mold. A good vapor barrier on the floor and rigid insulation on the walls as illustrated in the link below.
BSI-009: New Light In Crawlspaces — Building Science Information

I always like photo #5.
Just a note, but during the heating season, 1/2 the air you breathe passes through that musty crawlspace.

Old 07-13-15, 08:09 AM
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Close the vents and seal with polystyrene. Make sure you have a complete VB. All areas overlapped and sealed and run up the outside walls to at least ground height.
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