Architectural Sheet Metal and Roofing
Architectural Sheet Metal and Roofing
This domain tests flashing, drainage, metal roofing, and weatherproofing. The goal is to shed water and allow thermal movement.
Core rules
- Flashing: base, counter, cap, step, apron, valley, and drip edge. Lap upper pieces over lower pieces so water runs off, not into, the lap.
- Drainage: size gutters and downspouts for roof area and local rainfall; keep outlets clear; use scuppers where parapets trap water.
- Standing seam: concealed clips allow panels to expand and contract. Fasten clips, not the panel pans, and use the specified clip spacing.
- Dissimilar metals: separate copper, aluminum, and steel to prevent galvanic corrosion; use isolating washers or tape.
- Underlayment: install an ice barrier at eaves in cold climates and maintain proper laps.
Worked example
A 20-ft copper roof panel sees a 100 F temperature change. Copper expands about 9.4 x 10-6 in./in./F. Expansion = 240 in. x 9.4 x 10-6 x 100 = 0.23 in. The reasoning: provide an expansion joint or clip detail that allows about 1/4 in. of movement; pinning both ends would buckle the panel.
Traps
Fastening through standing-seam pans; reversing flashing laps; putting copper against aluminum; using too few downspouts; and ignoring ice-dam protection.