Detail Work: Edges, Upstands, Outlets and Penetrations
Why details fail
Most leaks originate at details, not field membrane. Candidates must know how to form upstands, edge trims, drip edges, verge and eaves details, outlets, rainwater outlets, penetrations, and expansion joints. Upstands require a minimum height above finished roof level and a termination that prevents water tracking behind the membrane.
Forming details
Understand reinforcement at corners and changes of direction, fillet or chamfer at internal angles to avoid bridging, and the use of pre-formed outlets and collars at pipes. Know that drip edges must project beyond the wall face to shed water clear of the building.
Traps to watch
- Upstand too low, allowing water to overtop in wind-driven rain.
- No fillet at internal corners - membrane bridges and splits.
- Termination not mechanically fixed or sealed, letting water track behind.
- Outlet not reinforced, or fall not directed to the outlet.
Worked rule of thumb
For upstands, remember the H-T-R rule: Height above finished surface (per specification), Termination fixed and sealed, Reinforcement at corners and changes of direction. A detail that fails any of H, T or R is a defect waiting to happen.