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Crawlspace insulation



Our floors get cold in the winter, and I'd really like to fix that this summer, so I've been looking into crawlspace insulation.  Currently, there is nothing insulating our floors from the crawlspace, other then the subfloor.  Seems there are 3 options for a crawlspace


1) Close all the air vents, place plastic on the ground to prevent moisture, then place insulation around the outer crawlspace walls

2) Install insulation between the floor joists

3) Install a thick plastic membrane on the crawlspace ceiling (suggested by a home depot employee)


I don't feel comfortable with #1 as we live near the bay and the soil has a lot of moisture, and any holes in the plastic will allow moisture in and result in mold if the vents are closed off (theres a lot of sharp rocks/soil down there).  I don't like option #2 as it would be very hard to hang insulation in a 2ft workspace, and any moisture would rise to the top of the crawlspace, hit the moisture barrier, and condense in the fiberglass, bringing down the insulation.  Not to mention, if a mouse found his way in there, I would quickly have a nest in my crawlspace.


Option 3 seems like it wouldn't do much to be worth the effort. 


Is there another option?



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Posted 2011-07-11T19:39:38+0000  by travismikjaniec travismikjaniec

First off you never want to cover the vents. Think of this like your attic only in reverse. It's a cold zone so you need ventilation to prevent mold. But unlike your attic you have a dirt floor which wicks moisture so it needs a vapor barrier on the dirt. You'll notice that some insulation has a kraft paper backing. That is the vapor barrier. By installing it with the paper against the wood floor between the joists you allow moisture to flow through the insulation just like your attic but not condense on the wood above it. One last thing make sure you seal any cracks or penetrations in the floor before installing insulation.


Hope that answers your question


From a guy in the business

Posted 2011-07-12T04:52:11+0000  by dsentor

Hey dsentor.  Welcome to the Home Depot community!

Thanks for your tips.  Your advice is right on. 


Hello travismikjaniec.  A 2 foot crawlspace is really tight quarters to work in, but if you want a cure for cold floors, that is where you will find it.  While more and more homes have sealed, (conditioned), crawlspace areas, I think given the moisture issues that leaving the vents open is your best bet.  This rules out option 1.


Option 3 is a variation of using faced insulation without the insulation.  This will not make your floors any warmer.


As for option 2, keep in mind that the closer you get to the floor the warmer it will be.  Condensation happens due to cold, not heat.  Using faced insulation as dsentor suggests should work fine as long as the facing is against the floor.  I agree that with only 2 feet of space this will be a difficult job.  It’s also possible that mice can crawl up into the insulation, but the force of gravity will make this a poor nesting area.R19Floors.jpg



Owens Corning has a couple of videos that you might find helpful:


Owens Corning.JPG


You can find them at this link:  Videos


One video is for conditioned crawlspaces, the other for unconditioned spaces like yours.


Notice that in both cases it is recommended that you put down plastic sheeting on the floor.  To the extent that the plastic remains intact, it will help to keep moisture levels in the crawlspace air to a minimum.


Once again, welcome both of you to the community.

If there is anything else you need, we are here to help.


Posted 2011-07-12T18:35:41+0000  by Chris_HD_CHI
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