Base flashings, edge metal, drip edges, gravel stops and roof-to-wall transitions
Base flashings, edge metal and roof-to-wall transitions terminate the roof system and shed water away from the building. The exam tests edge securement, drip geometry, gravel-stop profile and transition sequencing.
Core rules
- Edge metal must be fastened to a continuous cleat or substrate, not just the membrane. Space fasteners per manufacturer and code; use compatible fasteners and washers.
- A drip edge projects beyond the wall or fascia and turns down so water clears the substrate. A gravel stop has a raised lip to retain ballast and a fascia face.
- Base flashing at a wall must extend high enough to remain covered by counterflashing after insulation and membrane thickness. Do not set the top edge at the finished roof line.
- Splice edge metal with expansion provisions; long runs need joints that allow thermal movement. Seal laps and end joints as detailed.
- Roof-to-wall transitions need a transition membrane or metal flange, a cant or fillet, and counterflashing that overlaps the base flashing.
Worked example
A reroof adds 4 in. of insulation to a low-slope roof, but the existing wall counterflashing is reused. The base flashing top edge now sits only 1 in. below the counterflashing, and the old reglet is at the original height. After settlement, the overlap opens. The correct repair is to extend the base flashing so it remains at least 4 in. behind the counterflashing, or raise the counterflashing in a new reglet. Do not simply caulk the gap; the base flashing must be mechanically lapped and the counterflashing must shed water over it.
Traps
Fastening edge metal through the membrane without a cleat; a drip edge that stops short of the fascia; reusing counterflashing after insulation is added; omitting expansion joints; relying on sealant at roof-to-wall transitions.