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stymie222 06-15-2011 08:21 PM

Should I insulate this ?
22'X30' addition- crawl space only. Block foundation walls.
I have installed 4'x8' sheets horizontally, of O Corning 2" foam board along entire inside of block wall foundation.
Do I now need to insulate between the 16"OC I Joists, or is the crawl space now insulated enough ?

autx790 06-16-2011 07:11 AM

Where are you located? At least down south, if you put fiberglass or even open cell spray foam in between the joists they will hold moisture and will not hold up and eventually could cause rotting unless you create an air tight seal around it. If you've completely sealed up the walls with insulation, you'll probably want to put down a moisture barrier along the ground.

stymie222 06-16-2011 07:20 AM

Live in Iowa. Very cold winters.
Would 6" thick batts be adequate for 9 1/2'" I joists, or go for the 9 1/2" batts ?
I don't know if this info is right- The Mid American energy consultant said I didn't need the I joists insulated if I installed the foam board. Kind of shook my head on that one.

I will put down 6mil poly on entire floor.

Thanks for the reply.

autx790 06-16-2011 08:17 AM

If the space is now sealed up i'm not sure how much gain you receive in insulating between the joists. I just know that if your going to seal up your crawlspace but dont put a membrane down on the ground, you will get moisture coming up from the ground.

You could read the info here on crawl spaces, they have some good info on how best to do all this.

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