Exposed Rockwool Comfortbatt in conditioned space?
canada_deck
| Posted in General Questions on
I believe you are allowed to have exposed Rockwool Comfortboard in your conditioned space. (e.g. as a thermal barrier over rigid foam when used to insulate rim joists in an unfinished basement.) Are you also allowed to have exposed Rockwool Comfortbatt within your conditioned space? Are there any concerns about offgassing or loose fibers if it is not behind a vapor barrier or drywall?
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Replies
canada_deck,
I don't think there is any explicit code interdiction against exposed batts. What would preclude it is that Canadian codes require a warm side vapour-barrier, so you would need either impermeable foam as you have on basement walls and rim-joists, or a membrane of some sort.
Fluffy insulation like rockwool aganst the rim joist is a risky because water vapor will find it way thru the insulation to the cold surface and condense into liquid water. Mold and rot seem likely.
https://www.greenbuildingadvisor.com/article/insulating-rim-joists
Walta
Thanks both. I'm uncertain about what to do with some rim joists.
Current situation:
- On the opposite side of the rim joists is a deck. When the deck was installed, the entire rim joist was flashed on the outside with a flashing tape that would act as a vapor barrier. (3M™ All Weather Flashing Tape, 8067.)
- Since this building was built, the rim joist cavities just had some loose pink insulation shoved in them. There have been zero issues with mold.
- As a part of a larger project, all the insulation in that room has been removed (including out of the rim joist cavities.)
So I now need to do something. One other note is that the shape of the room has a lot of angles so the cavities are all different sizes and shapes.
Options:
1) Leave them exposed. Seems like a poor option.
2) Shove loose permeable insulation back in those cavities (this time the Rockwool stuff). I understand it has risks but I could easily pull it out in a year to check if it has created any moisture issues and then adjust my approach if required. It didn't cause any problems over the past 30+ years in this particular room.
3) Shove the loose permeable insulation in those cavities and then add a poly vapor barrier sealed with staples and Tuck Tape. This means that I would not be sandwiching the rim joist alone between two vapor barriers. (In theory there could be some migration through the few inches of wood in the cavity.) With this approach, it would also be easy for me to cut off the plastic from one or two cavities in a year to check how they are doing and then easily staple it back on.
4) Foam inserts, spray foam around the edges, and then ComfortBoard on top as a thermal barrier. I realize this is the commonly prescribed approach but I worry about tightly sandwiching that rim joist on both sides with a vapor barrier and it will be the messiest to inspect down the road.
In a similar vein, I've been thinking about how to insulate the sections of concrete wall without needing to drywall over foam and while also ensuring some air flow if moisture behind the foam is a problem. Would it be crazy to put some of the insulated DriCore floor panels against the wall?
I would be concerned with fibers if it were me, that stuff can be pretty nasty. Also keep in mind you poly is also creating a vapor sandwich. You could use something like Henry vp100, they have a 12” roll that might work well and it is already adhesive (though you may need supplemental tape).