Pre-existing unvented cathedral ceiling– will there be problems?
My client has a house built in the 1970s with cathedral ceilings, a shallow (2 in 12) roof, 2×12 rafters, and T&G pine ceiling. The ceiling was insulated (looks like R-38 faced batts), but there is neither ridge nor soffet venting. The owner had a membrane roof put on about 2 years ago and now wants to remodel. I am concerned about an unvented roof with a relatively “leaky” ceiling– won’t there be issues with moist air getting into rafter space and condensing on the underside of the roof deck? Unfortunately, there is intermittent blocking between the 2×12 rafter bays, and it has a boxed soffet as well. He lives 100 yards from the ocean in climate zone 4 (mendocino coast). Any help is appreciated.
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Replies
Cynthia,
The builder definitely made a bunch of mistakes, but it's hard to predict if the roof will have problems. The colder the winter weather, the more likely this roof will have condensation problems. The higher the indoor relative humidity, the greater the chance of problems.
So, if winters are mild and the indoor air is dry, everything might be OK. If there is a cold winter, and if the indoor air is humid, the roof assembly could get very wet.
Most homeowners don't take any action until they see signs of a problem. But when it's time for new roofing or a new ceiling, it probably makes sense to correct all of the errors.
More information here: How to Build an Insulated Cathedral Ceiling.