Rim joist insulation in finished basement
AndyNelson
| Posted in General Questions on
Hello-
I’m in the process of renovating my basement and would like to insulate my rim joists. I would prefer to use EPS as it is generally easy to come by in my area. However, I know that code requires a thermal barrier (such as drywall) over the EPS. My question is whether I have to put drywall directly on the EPS, in the rim joist, or whether the finished ceiling (drywall) in the basement is enough to meet code.
Thanks
Andy
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Replies
I would check with your local building department. In my opinion, the ceiling should suffice here since the rim joist is no longer exposed to the occupied space, but there could be local code issues. You can usually use mineral wool over the EPS here to provide fire protection instead of drywall, and that’s easier to install and also provides additional insulation (make sure your EPS is thick enough for your climate zone if you go this route to avoid any moisture issues). Note that you CANNOT substitute fiberglass batts for mineral wool in this particular application. You have to use mineral wool here and not fiberglass since mineral wool is fire rated.
Bill
Thank you! I had not thought about mineral wool and I will have extra after I'm done insulating the above ground walls (it's a walk out). I was planning to go with at least 3" of EPS in the rim joist area which I think should be sufficient to address any potential moisture issues (i'm in 5a). Though I may have to trim the EPS back a bit to accommodate the mineral wool batts.
At any rate, thanks so much for the mineral wool suggestion. I will investigate my local code to ensure this will be fine before I do the work.
Thanks again!
Andy