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Ted's Energy Tips 
Great information here. I came searching for
Question:
I had a question that no one has been able to accurately answer.
Was curious if you had any thoughts on my situation.
Master bedroom and bathroom have vaulted ceilings approximately 13′ tall. Non vented, so no soffit or ridge vents. The ceiling is insulated with batt insulation. There is a ridge beam that is metal.The beam is sandwiched with 2x10s The 2x10s are only approximately.1″ above the finished drywall ceiling. In the summer the metal beam sweats. The sweat is getting onto the back of the ceiling drywall. The drywall has started cracking and a 3’x3′ piece has fallen off.
Question is will spray foam help remedy this problem.
If so could I just remove a few feet of drywall on both sides of beam and insulate with spray since this is an unvented roof. I was thinking of lowering the ceiling by 6″ and encasing the beam in closed cell foam. The lowering will also keep the 2x10s that are sandwiching the beam from coming into contact with the drywall. Trying to limit thermal bridging.
Thanks for your time,
Adam
Ok, so if it’s a summer problem, then the beam is staying cold enough for the condensation to form on it, like a beer glass in summer. If the beam is coated with spray foam, that cold surface will no longer be exposed to the air’s moisture and the issue should stop.
The potential problem is that any part of the beam that isn’t coated in foam is still going to be exposed and condensation may form on it. For example the top that isn’t accessible.
So, doing what you discussed will greatly reduce the issue but it won’t necessarily eliminate it 100%. But it’s probably the best solution you can hope for.
Question- do you think all the condensation is coming from the inside of the house or the outside? If you think it’s humid outside moisture getting into the roof and condensing on the beam, then you’d want to try to foam the beam from the top also, to fully encase it. That’s a pain as that would involve cutting back the top of the roof to get access. That would be the most thorough solution. But there’s no easy way to know if it’s necessary.
I’d start with your suggestion and see how it goes over the long term. You can go crazy looking for the perfect fix.