What layers make up a commercial flat roof system?
A commercial flat roof is a stack of layers, from the structural deck up to the edge metal, and each one handles a different load or exposure.
| Layer | Job on the roof |
|---|---|
| Deck | Steel, wood or concrete base that carries the roof and the people on it |
| Vapor retarder | Slows indoor moisture from reaching the insulation in humid or heated spaces |
| Insulation | Polyiso or similar boards that control heat flow and set the slope in tapered systems |
| Cover board | Thin, hard board that shields insulation from foot traffic and hail |
| Membrane | TPO, EPDM or another sheet that sheds water |
| Flashing and edge metal | Seals walls, curbs, drains and the roof perimeter |
Leaks on new roofs tend to start at flashing around curbs, parapet walls and drains, so those details get the closest attention during installation.

