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Old 03-10-2014, 06:41 PM   #1
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Insulating Rim joist help


Previous owner installed fiberglass and I wanted to replace them because they have mold on them. I went ahead and compressed fit 2in foam board,but there is about 1/2in space between them.

Is there a certain type of foam I should use to seal around the foam? I was going to buy some DIY closed foam spray to add more R value, but its a little pricey and wanted to know what you guys thought first before I went that route. Thanks
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Old 03-10-2014, 07:14 PM   #2
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Insulating Rim joist help


Expanding foam is what you need.

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Old 03-11-2014, 02:33 PM   #3
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Insulating Rim joist help


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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Old 03-11-2014, 05:54 PM   #4
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Insulating Rim joist help


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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Old 03-11-2014, 07:26 PM   #5
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Insulating Rim joist help


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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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Old 03-12-2014, 07:38 AM   #6
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Insulating Rim joist help


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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Old 03-12-2014, 08:12 AM   #7
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http://building.dow.com/na/en/produc...gapscracks.htm

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In contrast, GREAT STUFF™ is a closed-cell foam. It forms a water-resistant outer skin when cured.
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Old 03-12-2014, 08:26 AM   #8
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Insulating Rim joist help


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.
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Old 03-12-2014, 08:33 AM   #9
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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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Old 03-13-2014, 03:00 AM   #10
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Good find Mike.

Thanks.

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