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Insulating basement crawlspace


legopig's Avatar
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02-12-08, 04:25 PM   #1  
Insulating basement crawlspace

I recently bought a home with a crawlspace underneath, and am looking at adding insulation under the floor. I have read differing opinions when it comes to vapor barriers on the fiberglass batts - should I have them or not?
(The crawlspace is vented, with a bare earth floor that has stayed very dry through the wet winter so far, but is not covered with any vinyl/plastic sheeting.)

 
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02-12-08, 06:26 PM   #2  
Fiberglass insulation inhibits the flow of air and heat trapped between two surfaces. Without some kind of cover on the bottom, the batts under your floor would be more like air filters than flow stoppers. My living room is over a crawl space, and I plan to add batts and then cover the bottom of the joists with some of that foil-back "double-bubble" barrier material to seal it all up really well.

 
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03-03-08, 12:53 PM   #3  
Posted By: legopig I recently bought a home with a crawlspace underneath, and am looking at adding insulation under the floor. I have read differing opinions when it comes to vapor barriers on the fiberglass batts - should I have them or not?
(The crawlspace is vented, with a bare earth floor that has stayed very dry through the wet winter so far, but is not covered with any vinyl/plastic sheeting.)
A vented dirt crawlspace is more liklety to stay dry in the winter than in the summer. The reason for this is that hot air holds more moisture than cold air. When this warm air enters your crawlspace in the summer, the cooler air of the crawlspace will cool the air entering through the vents and raise the relative humidity. The newly-cooled air cannot hold as much moisture as it could before, and it drops the extra moisture on whatever surfaces it can find, which makes everything damp and moldy.

This isn't the worst part. Warm air rises. As the air leaves your home through the upper levels, it's going to suck air from the lower levels, including your crawlspace. The humid, moldy air is going to rise into your home and into your lungs. If you insulate your subfloor, that humid air will pass through the insulation, making it moist, which causes it to lose its value as insulation.
Our web site has a lot of good information about wet and moldy crawlspaces that you should check out. <A HREF="http://www.basementsystems.com/crawlspace/">Click here to check out or crawlspace products</a> or <A href="http://www.basementsystems.com/learning_center/mold/">click here to see our tutorial on mold and moisture in crawlspaces.</a> It's worth doing a little research on.

~Jacques

 
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