Does a metal roof have felt under it?
Short answer. A properly installed metal roof on a house has underlayment beneath the panels, but today it is usually a high temperature synthetic sheet or self-adhered membrane rather than traditional asphalt felt. Older metal roofs, especially on barns, sometimes have felt or nothing at all.
The layers under a typical residential metal roof
- Solid decking: plywood or OSB fastened to the rafters or trusses.
- Self-adhered leak barrier: at eaves, valleys, around chimneys and skylights, and over the whole roof on low slopes. It should be rated for high temperatures.
- Synthetic underlayment: over the rest of the deck, also rated for the heat metal produces.
- Slip sheet, if required: some standing seam systems call for one so panels can slide as they expand.
- Metal panels: fastened with clips or screws, with trims and closures at edges.
Why felt fell out of favor under metal
- Felt absorbs moisture and wrinkles, which can show through thin panels.
- Asphalt in felt can soften and stick to hot metal.
- Synthetics are lighter, stronger, and hold up better if exposed to weather during the install.
Felt is still permitted in many cases, but most metal manufacturers now recommend high temperature synthetic or membrane products.
How to check what is under yours
From the attic you will usually see only the underside of the decking. At a gable or eave, a roofer can lift a trim piece to see the underlayment. If you see panels fastened straight to purlins with daylight between them, there is likely no underlayment.
Read synthetic underlayment vs felt and metal roofing in Georgia.