Should a metal roof be vented?
Why metal does not change the rule
Ventilation exists for the attic, not the roofing material. Moist air from cooking, showers and breathing works its way into the attic, and Georgia summers add plenty of their own humidity. Without airflow, that moisture condenses on the coldest surface. Metal cools quickly at night by radiating heat to a clear sky, so its underside can drop below the dew point even on mild nights, which is why unvented metal over a damp space drips.
How metal roofs are vented
- Ridge: a vented closure or profiled vent under the ridge cap that matches the panel ribs, so air leaves while insects and rain stay out.
- Eaves: soffit vents feed the attic as usual. Some systems also use vented eave closures.
- Underlayment: a high temperature synthetic underlayment over solid decking protects the deck from any condensation that forms.
- Open framing: on porches, sheds and barns where panels sit on purlins with no deck, an anti-condensation fleece backing on the panels keeps drips off whatever is below.
When a metal roof is not vented
Some homes use an unvented design with spray foam against the deck. That is legitimate when it is designed as a whole, with insulation and air sealing to match, but it is not the same as simply leaving out the vents. If you are switching from shingles to metal, keep the existing ventilation plan unless the whole assembly is being redesigned. More in metal roofing in Georgia and roof ventilation basics.