Faced or unfaced?
I have talked to you before. Hopefully you can help me once more. I’m in Zone 2a. The building is metal. It’s going to be a/c only.
I wanted to foam it — but $$$$, so I’m going to put a vapor barrier in the cavity, an air space will be maintained at the metal, then put a Johns Manville wool/fiberglass batt in the wall, then drywall and paint.
Now, the ceiling is the Q. I think that the insulation in the ceiling should be kraft-faced to the cool side. The soffits will have vent panels installed and I’m going to put a reflective product in between the roof rafters to help control heat. I’ve been told not to do the kraft-faced paper, but I don’t see why. In the end I hope to end up with about R-40 +/-. What do you think?
Thanks again. Keep up the good work!
Bill
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Replies
Bill,
Traditionally, kraft facing is faced to the warm side of the assembly. In a heating climate, it usually faces the interior. In a cooling climate like yours, it would make more sense for it to face the exterior.
But vapor retarders are not required by code in your climate zone, nor are they needed for this type of insulation. Unfaced insulation is fine. If you have faced batts, you should face the batts toward the hot side of the assembly. But don't worry about it.
Vapor barriers aren't necessary in zone 2A, but "smart" vapor retarders such as kraft facers (on either side) are fine. They become vapor open when the humidity is high, and will not create a moisture trap.
You do need AIR barriers on both sides of any fiber insulation to be fully effective. It's fine to use radiant barriers facing an air gap on the exterior side, though it's pretty expensive for the modest performance it adds to an R40 assembly. If you go that route, PERFORATED aluminized fabric versions of radiant barrier still offers reasonable drying capacity into the air channel (at about 5 perms), while still being sufficiently air-retardent for getting the full performance out of the fiber.
In regards to face/unfaced, I talked to a person at a insulation mfg co. She had said that I could take faced ins an turn it around put the paper to warm side [toward the metal] an use it as vapor barrier/retarder. Would this work??? TKS BILL
Bill,
If you read my first answer (Comment #1), you'll see that I already addressed your question. I wrote, "If you have faced batts, you should face the batts toward the hot side of the assembly."
Yes, this will "work." A vapor retarder is a vapor retarder. Facing it toward the warm side of the assembly is the correct way to face it. But stop worrying about it -- this detail doesn't matter very much.