I have a low slope unvented vaulted/cathedral ceiling that I am reinsulating. I have applied 1.5" of closed-cell spray foam insulation to the underside of the sheating and I am going to batt the rest of it. My main question is concerning whether or not to use faced or unfaced batts. I have been told that it shouldn't matter if I use faced batts because the ceiling is unvented and no moisture should get in, and the only moisture that would get in would be from the inside of the house so the faced batts would be better anyway. On the other hand, I have been warned about creating the double vapor barrier...so, faced or unfaced?

Key word: "no moisture should get in".

It is very difficult (practically impossible, actually) to seal construction so that no moisture ever gets in, so it's best to assume moisture will get in, and design the assembly that way. In your case, having already installed spray insulation directly to the underside of the roof plane, I feel you have gotten off on the wrong foot. What should be directly under the roof plane is a ventilated air space. The absence of vents, and an air space in the wrong place, if there is one at all, will surely invite trouble, so it hardly matters what you do in the rest of the assembly.

I would first check to see if 1.5 inches of closed cell foam is enough to prevent condensation. You are in the northern part of the country, so it may not be enough. Personally here in Minnesota, I wouldn't take that chance. As far as batted vs unbatted. I would go with unbatted if you can. Batts are a very unreliable vapor retarder so vapor is going to get through anyway, so the batts may work against you.

Thanks for the responses...
Richard--I understand that some feel unvented is better than vented, while I know people (and I have read various literature) who swear that an unvented cathedral ceiling is the way to go. So, pick your poison I guess...cathedral ceilings are difficult to insulate. Mine is unvented with no ridge vents or soffit vents, thus making it a vented roof would have been quite the undertaking, so I am trying to make the best of what I've got and just seal everything up tight. I also note that I have a metal roof that was installed on top of a built up roof. I only say this because the metal roof does not sit directly on the sheating...ther is an inch and half of built up roofing in between, thus in theory, the sheating would not get as cold as it would if the metal was directly on the sheating.

Any other comments about faced vs. unfaced batts would be welcomed also. Thanks for the speedy replies!