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Old 12-29-2014, 01:36 PM   #16
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Save the foil faced stuff. It won't serve any purpose here used in this assembly.
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Old 12-29-2014, 05:01 PM   #17
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Would you recommend any vapor barrier then? I thought the foil was what lowered the perm rating.
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Old 12-29-2014, 06:54 PM   #18
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Perhaps WoW was thinking that without an air space the foil wouldn't radiation decouple the floor from the concrete slab .... IMO, use the faced as it is a vapor barrier which is exactly what you want in your application. Hot exhaust, warm engine parked just after driving in rain/snow will deposit a large amount of moisture on the ceiling, you don't want that in your FG with only 1" of foamboard because of the higher perm rating (vapor open) than 2" XPS. As per article is fine, it mentions above a garage there as well.

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Old 12-30-2014, 08:19 AM   #19
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I was referring to the radiant barrier portion of the ISO as noted by Gary.

I would stick with poly faced XPS. Should be cheaper and tends to be a bit more flexible as well. It will give you all the perm rating resistance that you need out of that assembly.
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Old 12-30-2014, 10:25 AM   #20
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We just went through the same thing last year, and were very happy with the results, R30 batts fiberglass batts in the ceiling, R13 fiberglass batts in the 2x4 walls, 1/2" foil backed Poly ISO, then 5/8" drywall on top. The air sealing with the rigid foam made a huge difference, garage is basically a conditioned space now. I can't remember why we went with foil backed Poly ISO, but I don't think at the 1/2" it was much more expensive.
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Old 12-30-2014, 09:42 PM   #21
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Thanks again Gary and WoW.
I'll be price comparing foil and poly faced XPS tomorrow and will be moving on it by New Year's.
Ocelaris: thanks for commenting. I was reading through your thread from last year. I wanted to ask how the project turned out but haven't hit my requisite 15 posts for a PM. Good to know you're happy with the results.
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Old 12-31-2014, 09:51 AM   #22
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I just dropped you a line with some links to pictures. One thing you might consider is putting some OSB behind the drywall in some places so you have something to screw into. It's very difficult to find a stud with insulation over drywall. On the inside walls we put Poly ISO, but on the outside walls without 1/2 poly iso we put OSB behind the drywall to attach shelves, hang ladders etc... Here's a quick run down, and my PM has links to more.










Finished

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Old 12-31-2014, 11:01 AM   #23
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Great work Ocelaris!!

Thanks for posting that up. Looks fantastic!
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