I am going to insulate my rim joist in preparation for installing staple up pex. What thickness foam should I use? Is 2'' good or should it be thicker?
dave11 said:I used the 2 inch thick Foamular, R-10. Any thicker and it gets hard to cut and place, though I'd recommend cutting it on a table saw if you have one, to get really neat cuts. I had read that the foamular is better than using any foil-faced insulation, which could in theory trap moisture against the rim joist, though I'm not sure how much that really happens. Since you're installing radiant, you probably will need to leave an air space between the foamular and the radiant reflector, to keep the joist bays warmer.
velvetfoot said:Here's a thread with my tortuous journey.
I went crazy. It gets harder and more expensive with more layers.
https://www.hearth.com/econtent/index.php/forums/viewthread/31340/P0/
pybyr said:I agree that expanding foam can be useful for this, especially if you have varying sizes/ spaces to fill in addition to easily-cut foamboard shapes. I got one of these last December--
http://www.stonetooldepot.com/index.asp?PageAction=VIEWCATS&Category=328
-- if you're going to be doing this (expanding foam) in any quantity, it's far easier, more controllable, and less expensive than the hardware -store throwaway can-with-straw foam dispensers. You can also use part of a foam cartridge, close the gun (via a knob on the back) and set it aside for hours or maybe even days - and then come back and use the rest of the foam (unlike the throw-aways that clog themselves shut if set aside for more than a brief while). Just _don't_ get it on you- it's quite an adhesive (I've actually used it for that, also, in a pinch, and for non-critical uses).
You can get these other places, but the above place has a location near me, and their prices seem better than some other options I'd found (and they're good folkls)