Place rigid roam against the rim joists,then caulk along the insulation. Airtight insulation reduces heat loss through the rim joist (band joist). Fiberglass insulation and expanding foam seal the open top of hollow concrete blocks. The main benefit of weatherizing the basement rim joists is air sealing. It's not so much about insulating that area, so perhaps this article should be really be . Dec 1, 2014 - The second issue concerns the best way to insulate rim joists. . Your trying to win arguing with him and all the rest of us is getting old. Fun to . Dec 13, 2011 - Without a vapor barrier at the rim space, you'll have relatively warm, moist air passing through the fiberglass insulation and then condensing at the rim joist. This can create mold or rotting. There are only two ways that I ever recommend to insulate the rim space: rigid foam or spray foam. Oct 10, 2018 - The interior of a basement wall can be insulated with rigid foam or closed-cell spray foam. . and Victoria) concluded that 'for all types and sizes of basements . It's easier to insulate and air-seal the rim joist area with exterior . Foam board insulation at rim joists Foam Board Insulation, Basement Insulation, Home . Before & After: Air Sealing Around Rim Joists in Neenah, WI - Dr. Uninsulated rim joists are huge energy losers. Now's the time to insulate and seal your rim joists. One option is to seal the rim joists with rigid insulation cut to fit. I live in an older home with a small unfinished basement and wanted to insulate the basement rim joists. I was looking around and the best .