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Heating & Air Conditioning

Insulating a crawl space addition

15 years ago

I have 15' x 12' crawl space addition off my family room that is colder than other rooms in the house. There is no insuation in between the joist, or along the foundation walls. There is very little space to crawl into the crawl space add insulation underneath.

I see 2 options:

1 Is it effective to insulate the outside walls with rigid foam, if so what would you recommend?

2. I am having the house resided from Aluminum to a Hardie Fiber Cement product. While the sidding is off can the rim joist be removed and the interior walls of the foundation be insulated? If so what material would you recomend. Would this be effective as well?

Thanks,

SAK

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Comments (3)

rjoh878646
15 years ago
Insulating the outside is not that feasable. The foam board used for ground contact is R-5 per inch. To get any insulating value would require 2-3"'s. Plus you have to flash it at the top, bury the bottom edge into the ground and coat it with a special stucco material to keep it from self destructing from UV exposure.

You do not remove rim joists on a whim. They are removed and replaced when the have rot issues. Removing a rim jost requires jacking the house up. No easy task,and no fun. This is the voice of experience.

You have 2 solutions to insulate, get in the crawlspace and lay down a 6 mil vapor barrier and use fiberglass, or hire someone to spray closed cell foam in between the floor joists and on the interior side of the exterior walls of the crawlspace. Expensive,effective and waterproof.
sakskc
Original Author
15 years ago
rjoh,

Thank you for the informative reply.

Regarding the spray foam option:
Is this an expanding foam that can be sprayed inbetwen the joist without support like a net?
How would it be sprayed between the joist, by drilling through the Rim Joist?
Will this require the vapor barrier?

crawling under the crawl space is only possible for a Hobbit, the floor to joist height is 16" max

Thanks,

SAK
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pjb999
15 years ago
Not sure how keen/how much room someone doing the spray foam would need, it MAY be possible for them to squeeze in that space, the good news is, the spray foam needs no support and no vapour barrier, as it acts as its own air/vapour barrier and is highly effective as an insulator.

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