I’m almost finished with my new metal building. It’s basically a wood post and beam, metal sheathed garage…no insulation, no interior finish, no plywood roof decking. The metal is exposed on both sides. The top two feet of the side walls are screened for light and ventilation. (In fact, one end wall is still open.) I know about the principles of condensation, but did not expect it to occur because the temperature above and below the metal roof is equal and there’s plenty of air flow. Do you think interior roof insulation with a vent space above would solve the problem or merely catch the drips?
Dave
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Although the air is presumably quite close in temperature above and below, the metal is often not the same temperature as the surrounding air as it heats and cools more slowly.
Airflow only does so much to eliminate condensation, that's why the standard detailing for metal roofs has moved away from skip sheathing to sheet underlayments in direct contact with the underside, which appears to be more effective - sort of like the insulated roof of a car.
Before you go too far trying to remedy the problem you might want to watch it for a while. We built a metal shop that had heavy enough condensation that it rained inside for the first month, but has never had any problem since.
I've dealt with this a couple of times for one customer--remove the metal roofing (installed over purlins with no felt), remove the purlins, install a CDX deck, install Ice and Water Shield over the entire deck, and reinstall the metal roofing. It solves the dripping problem.
Google 'night sky radiation'... interesting reading.