Roofing Systems and Moisture Management
Roofing and moisture-management questions test membrane identification, drainage, flashing, and how you report leakage risk without guessing at remaining life.
Membrane types
Low-slope membranes include built-up roofing, modified bitumen (SBS or APP), EPDM, TPO, PVC, metal, and spray polyurethane foam. Steep-slope roofs include asphalt shingle, metal, tile, and slate. Identify by seams, surface texture, and coatings; do not rely on color alone.
Drainage and details
Key details include roof drains with strainers, scuppers, overflow drains or scuppers, crickets and saddles, roof curbs, expansion joints, parapet copings, terminations, and penetration boots. Ponding is standing water 48 hours after rain and points to insufficient slope, blocked drainage, or deck deflection. Overflow outlets should sit above the roof surface but below the parapet or curb height.
Worked example
A TPO roof over a warehouse shows ponding near two drains, a crushed drain strainer, and an overflow scupper set 2 inches above the membrane. Reasoning: the crushed strainer restricts flow; the scupper is too high to provide backup drainage before ponding loads the deck. Report both, recommend a roofing contractor clear and repair the drains and evaluate slope, and note that widespread ponding may indicate structural deflection.
Traps
Pronouncing remaining roof life from a walk; calling a roof failed because of blisters; missing overflow drainage; and walking a wet or fragile roof. Also: treating an interior stain as proof of an active leak when the cause is unverified.