How should insulation work with a metal roof on a house?

Metal over a solid deck

• The metal itself adds almost no insulating value.
• Attic floor insulation, air sealing and ventilation work the same as under shingles.
• Synthetic underlayment between the deck and the panels manages any condensation that forms on the underside of the metal.
• Rain noise is usually muted by the deck, underlayment, attic and ceiling insulation.

Metal over open framing

On porches, carports and detached buildings with panels screwed to purlins, warm humid air hits the cold underside of the metal on clear nights and condenses, raining back down. Solutions include a condensation control membrane or felt backing on the panels, faced insulation with a vapor retarder, or a solid deck with underlayment.

Spray foam under the deck

Spray foam under the roof deck creates an unvented attic and works with metal like with shingles, as long as it is built to the code's unvented attic rules. It also hides leaks, so flashing details must be excellent.

Reflective finishes

Light colored and cool rated metal finishes reflect more sunlight, cutting heat gain into the attic. In Georgia sun, that can matter as much as adding insulation.

Ventilation still matters

A vented attic under metal needs intake and a metal compatible ridge vent with vented closures. See metal roofing in Georgia and best shingle colors for Georgia heat.