Ventilation under Metal for Cathedral Ceiling?

jason Levasseur
I am having a bit of trouble finding the “final word” on the need for ventilation of a metal roof over a cathedral type ceiling. Do I need to provide continuous ventilation from the soffit to the ridge -- between the insulation and the sheathing -- the same as one should do with an asphalt shingle roof? -- Thanks.
Eric Novotny
An informed customer is the Best Customer!
Why type of penetrations are in the Cathedral ceiling, if any? Is there any ventilation now? Did the roof ever sweat before? What is the existing construction, insulation type, and depth? Ventilation has nothing to do with shingle (roof material) cooling. It sole purpose to to prevent condensation as a result of the migration of warm moist air from the living space below. If you are insulation with something like spray foam or have a tight envelope (air barrier) the necessity for ventilation is nil.
Todd Miller
Isaiah Industries, Inc.
The international building code does call for ventilation in these circumstances. Older homes which maybe got by without ventilation did so because other parts of the house were not airtight. However, over time, we ten to make houses tighter and we also introduce more moisture sources into them. That creates a recipe for condensation when homes are not vented. As you stated, metal roofed homes need ventilation same as do homes with other types of roofs.
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