Insulating ceiling over unheated basement
bunderwater
| Posted in General Discussion on
I want to insulate the ceiling above an unheated basement. It’s not feasible to properly insulate the basement now, so I just want to insulate the ceiling so the floors aren’t as cold In the space above. Climate zone 4b.
The floor joists are exposed, and 7” deep. There is no vapor barrier anywhere currently.
what I’d like to do is put up 7” (two layers of 3.5” R-15 – unless one is enough) of rockwool between the joists, but I think I need a vapor barrier below the subfloor. what kind of vapor barrier would be best for this? Something to put up between the joists against the subfloor, and then put rockwool up between the joists?
Replies
Why 2 layers of 3.5"? Rockwool comes in 7.25" thick R30 batts sized for 2x8 joists. Don't know about the vapor barrier. Is the basement at exterior temperatures?
The basement isn’t at exterior temps, but not that far off. Low 50s (F) when outside temps are high 30s, for instance. The room above might be at 70F. Two layers or one, just a function of what I have/access. A bit easier to get the 3.5” thick stuff.
I do not think you need a vapor barrier in your zone.
If you cannot insulate the basement now, you might get better results by sealing and insulating the rim joist above the basement wall. (and making sure the rest of the basement wall is sealed as well as you can.)