Mineral wool vs rigid foam for joist cavities
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| Posted in Energy, Heating & Insulation on
There is a stud wall between my conditioned living room and unconditioned garage where the joist bear down on a beam in my garage. I want to insulate the joist cavity this weekend as I’ve torn all the drywall down. I was thinking it would be easy to just cut a piece of R23 mineral wool and pressure fit it into the cavity. I was also thinking of cutting and cobbling rigid foam. What are the expert opinions on either? I was thinking mineral wool would be faster/easier, but provide less of an air barrier. I will eventually cover the ceiling of the garage with rigid foam to act as insulation/air barrier for the 2nd floor “garrison” that is overhanging into the garage as well.
Replies
You've basically nailed down the pros/cons of the rigid vs rockwool. Generally speaking attached garages should be outside of the thermal/air barrier of the conditioned space, so rigid would be the better option in this case since rockwool is not an air barrier.
If your cavities are pretty uniform, you can cut and cobble the rigid foam pretty quickly. Leave some space on the edge and finish with canned great stuff foam.
Which side of the wall have you removed drywall from?
rigid foam boards will require lots of fussy work to get installed and sealed. (a Pro foam gun will help a lot if you decide to do it this way)
you might be better off with another method of vapor barrier and air sealing, and go with the fiber insulation.
You need an acceptable fire barrier between the garage and home. (drywall of the proper thickness will do)