Roof flashing: the kinds, where it goes, and the code's rules for each
Flashing is the metal, or sometimes roll roofing, that seals the joints where a roof meets a wall, changes slope or direction, or is cut for a chimney, vent or skylight. The code calls for it at every wall-roof intersection, change of slope and roof opening, in corrosion-resistant metal at least 0.019 inch thick (No. 26 galvanized), with a cricket behind any chimney wider than 30 inches (IRC R903.2).
Anthony Hicks30+ years in construction. Updated November 5, 2026.
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Where flashing goes
The code calls for flashing wherever water could get in at a joint (IRC R903.2.1):
- Where a roof meets a wall, along the side or at the top of a slope.
- Wherever the roof changes slope or direction, such as a valley or a break in pitch.
- Around roof openings: chimneys, vent pipes, skylights.
- Where an eave runs into a sidewall, a flashing that turns the water away from the wall, often called a kick-out.
Metal flashing has to be corrosion resistant and at least 0.019 inch thick, No. 26 galvanized sheet (R903.2.1).
The kinds
| Flashing | Where | What the code says |
|---|---|---|
| Step or continuous sidewall flashing | Where the roof slopes up beside a wall | At least 4 inches high and 4 inches wide, turning water onto the roof or into the gutter, its upright leg under the siding (R905.2.8.3) |
| Base and cap flashing | Around chimneys and at walls | Base of metal at least 0.019 inch or mineral-surfaced roll roofing of at least 77 lb per 100 sq ft; cap of metal at least 0.019 inch (R905.2.8.1) |
| Kick-out | Where an eave meets a sidewall | Diverts water away from the wall (R903.2.1) |
| Valley lining | Valleys | At least 24 inches wide in metal for an open valley (R905.2.8.2) |
| Drip edge | Eaves and rakes | Lapped 2 inches, nailed at 12 inches or closer (R905.2.8.5) |
| Vent pipe flashing | Pipes through the roof | Installed to the shingle maker’s instructions (R905.2.8.4) |
The guide to roof valleys covers valley linings and the drip edge guide the edges.
Chimneys and crickets
A chimney gets base flashing at the roof and cap (counter) flashing over it. On the uphill side of any chimney or penetration more than 30 inches wide, measured across the slope, the code calls for a cricket or saddle: a small peaked roof that splits the water around it, covered in sheet metal or the roofing (IRC R903.2.2). A skylight flashed to its maker’s instructions can go without one.
Common questions
What are the types of roof flashing?
Step and sidewall flashing, base and cap (counter) flashing, kick-out flashing, valley linings, drip edge and pipe flashing, each in a place the code names.
What metal is roof flashing?
Corrosion-resistant metal at least 0.019 inch thick, No. 26 galvanized sheet, under the residential code (IRC R903.2.1).
Does flashing get replaced with a new roof?
Step flashing, pipe boots and drip edge are lines on a reroof estimate, each priced on its own: by the piece, by the linear foot, or as a reset where the old metal is reused.
Why does a roof leak at the chimney?
A chimney breaks the roof plane, so it relies on its base and cap flashing, and on a wide chimney its cricket, to shed water.