# Insulating Rim joist help



## joecaption (Nov 30, 2011)

Expanding foam is what you need.


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## Windows on Wash (Aug 30, 2011)

For a nice fit like that, you can just caulk the seam.

Expanding foam is open cell but does control the air movement. You should have enough vapor permeance control with the 2" XPS in there.

If you want to go fast, get a froth pack and just spray it.


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## word2yamutha (Mar 13, 2013)

Thanks for the replys guys. Is there a certain type of foam I should use? Im not sure which of the great stuff product foams to use? Does the foam have to be flame retardant?


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## mikegp (Jul 17, 2011)

Windows on Wash said:


> Expanding foam is open cell but does control the air movement.


 
I thought great stuff was closed cell? 

I would use Great Stuff gap and crack filler.


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## Windows on Wash (Aug 30, 2011)

I will have to read up on it but the stuff that expands rapidly is typically open cell (i.e. open cell expands much greater whereas closed cell does not).


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## mikegp (Jul 17, 2011)

http://building.dow.com/na/en/products/sealants/gapscracks.htm



> In contrast, GREAT STUFF™ is a closed-cell foam. It forms a water-resistant outer skin when cured.


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## mmoses101-1 (Oct 16, 2012)

mikegp, great info! I've always assumed that it was oc. In most applications that people are using GS it probably doesn't matter but it's good to know.:thumbsup:


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## mikegp (Jul 17, 2011)

Also, if you don't want it to expand too much get the Window and Door foam. I used the gap and crack foam on a door once and it pushed the frame out even though it had other directions to expand. I had to shave the frame down to get the door to close.


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## Windows on Wash (Aug 30, 2011)

mikegp said:


> http://building.dow.com/na/en/products/sealants/gapscracks.htm



Good find Mike.

Thanks.


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