Insulating a Dirt Floor Crawl Space - Cold Weather Climate

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Posted by: from Odessa
3/22/2014 at 10:20:50 AM


In the process of buying a house. A wartime era 1.5 story house, which had an addition added maybe 10~ years ago (10'x20'). The house has a full basement, but the addition is just a crawl space. Noticed the floor in the addition was rather cold, and low and behold there is no insulation in the crawl space. There is currently poly on the dirt floor and duct work both in and out of crawl space to move the air around.

What I was contemplating was putting batt insulation in the joists, spray foaming any nooks and crannies that misses, putting up a 1 1/2" rigid insulation on the underside of the joists with taped joints to act as a vapour barrier (breaking the vapour barrier on the warm side rule) and then re-doing the poly on the ground with an accoustic seal around the block wall.

I'm sure my next issue will be looking into getting the knee wall in the attic properly insulated also.

Thoughts, opinions?

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Date/Time3/22/2014 at 12:18:49 PM

Sounds like you know what your doing.

Be sure you seal the foam insulation properly against the foundation as well. Then you have a complete vapour.

But you have the right idea. And sight unseen, should work well for you.

James Fram

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Date/Time3/22/2014 at 12:24:14 PM

James Fram again. Sorry if my last post threw you off.

Your vapour barrier must be on the inside/ warm side. You can put poly within and around all of you floor joists. Be sure to Tuck tape them well. Then add your insulation. The foam board insulation is great inside basements, because it can act as you whole vapour barrier plus the insulation. But in your case I would go with a high R factor fiberglass pink or robuxel insulation.

James Fram

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Rodney from PGCrenovations in Cambridge
Date/Time3/22/2014 at 7:44:15 PM

Insulating is a great idea but, if done wrong can be a big repair. Your best way to insulate the crawl space is spray foam. You might think it is expensive but trust me, it will be far better than anything you are thinking of and please don't take that the wrong way. By the time you add up all the labor you are going to put into this plus materials and gas running to the building supply store. Forget it, hire an insulation company to spray an R-12 into the crawl space where needed and enjoy a warm floor and the saving from lost heat in the crawl space.

I applaud your effects but even us pros have to use spray foam, sometimes it better for our clients.


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