Q: My house is a tri-level and the windows on the second floor are very close to the lower roof, so there’s really no room to add strapping over my existing shingled roof. The problem is that I’ve read on your site that it’s code to install metal roofing over strapping if you have a cathedral ceilings below. I have cathedral ceilings under one part of the roof with no access to the attic on the other side of the gable. That is; one side of my gable roof is a vaulted ceiling with no attic and the other side of the gable roof has a small attic space with no access to that space. There is a ridge vent with soffit vents, but I doubt very much if there were baffles to encourage air movement installed on the vaulted side since the house was built in 1979. Do I have to worry about condensation under the vaulted ceiling part? The roof deck doesn’t seem springy to me now and I imagine the issue has been there all this time with a composite shingle. One more thing. We have experienced problems with ice damming even though we have 2′ vented overhangs. I’ve found that I have to keep the ridge vent cleared of snow in the winter to keep it open and venting. Has anyone else had this problem. I’m not getting out there on a metal roof in the winter, so should I consider putting in a turret vent?
A: The ice damming is a result of the construction method. Unless something is changed, a metal roof will likely have little impact on that. It may help some but probably not much.
It really is not code to have battens underneath metal roofing over vaulted ceilings. The code says all roof systems need at least 1/2″ vented space. It is not particular to metal.
The problem I have seen though is that because metal roofing transfers cold easily you could end up with a condensation issue that did not exist before.
I would suggest adding ventilation if at all possible. If impossible, then an airgap or even a thin insulation board would be helpful, based upon what your roofing manufacturer suggests.
If it is impossible to do either, frankly, I would consider not using metal in order to avoid the chance of changing the thermal dynamics in a way that results in condensation issues you have not had in the past.