What are the correct flashing details for a roof-to-wall intersection?
Short answer. A correct roof-to-wall detail layers, from the deck out: self-adhering membrane turned up the wall, step flashing at least 4 by 4 inches under the code and at least 2 inches longer than the shingle exposure, nailed only to the deck, a kickout at the bottom, housewrap lapped over the flashing's wall leg, and siding or counterflashing over that, held off the shingles. Each layer must lap so water always lands on the layer below it.
The checklist, in installation order
- Membrane. Self-adhering ice and water membrane on the deck along the wall, turned up the wall sheathing several inches. GAF allows 4 by 4 inch step flashing only when a full 36-inch width of its leak barrier runs along the wall and at least 5 inches up it.
- Kickout first. At the bottom of the wall, where the eave meets it, install the kickout so the first step flashing laps over it.
- Step flashing. Code minimum 4 inches up the wall and 4 inches onto the roof; GAF's preferred size is at least 5 by 5, with each piece at least 2 inches longer than the shingle exposure. One piece per course, nailed to the deck only, high on the roof leg.
- Housewrap. The water-resistive barrier laps over the wall legs of the step flashing and kickout. Tucked behind them, it becomes a reverse lap.
- Siding. Installed over the housewrap, stopping above the roof by the siding maker's required clearance, with no nails through the step flashing.
- Masonry walls. Counterflashing set into a mortar joint, lapping down over the step flashing's wall leg.
Headwall detail
- Membrane up the wall.
- A continuous apron over the top shingle course, with generous legs on the roof and up the wall.
- Housewrap and siding lapped over the vertical leg and held off the roof.
Where the details meet
- Corners where a sidewall meets a headwall or a dormer front need a pre-bent or soldered corner piece, lapped so the upper piece always sits over the lower one.
- A valley ending at a wall needs extra membrane and a diverter so valley water does not dump against the wall.
- Windows close to the roof need enough clearance for proper flashing and siding laps.
Georgia's adopted code is the 2024 IRC with state amendments as of January 1, 2026, and the shingle maker's instructions add their own requirements. See roof flashing explained and ice and water shield in Georgia.