What is metal roof flashing, and what pieces does a metal roof need?
Short answer. On a metal roof, flashing is the set of formed metal trim pieces that seal every edge and transition: eave trim, rake trim, ridge and hip caps, valley pans, sidewall and endwall flashing, and transition pieces where the slope changes. They are usually made from the same steel and finish as the panels and sealed with foam closures and butyl tape rather than caulk.
The main pieces
- Eave trim: along the bottom edge, directing water into the gutter.
- Rake or gable trim: covering the panel edge along the sloped sides.
- Ridge cap: covering the peak, often vented, with foam closures underneath to block wind-driven rain and insects.
- Hip cap: the same idea along the hips.
- Valley pan: wide metal in each valley under the panel ends.
- Sidewall flashing: where the roof runs alongside a wall, tucked behind the siding or covered by a counterflashing.
- Endwall or headwall flashing: where the top of a slope meets a wall.
- Transition flashing: where the slope changes pitch.
- Pipe boots and curb flashing: for vents, skylights and other penetrations.
How it differs from shingle flashing
Shingle roofs use small step flashing pieces woven into each course. Metal panels are long and continuous, so their flashing comes in long formed pieces sealed with closures and tape. Metal also expands and contracts with temperature, so trim on standing seam systems is attached in ways that let panels move without tearing the seal.
Match the metal
Flashing should be the same metal and coating as the panels. Copper and lead should never touch galvanized or Galvalume steel, because they corrode it.