How should roof penetrations (vents, pipes) be flashed?

• A. With heavy caulk only without flashing.
• B. With metal flashing, sealants, and counterflashing integrated with shingles.
• C. By not flashing to allow expansion joints.
• D. By placing a plastic cap without sealant.

Answer: (C)

Flashing around roof penetrations must create a continuous, weather-tight seal that sheds water away from the opening and moves with the roof as it expands and contracts. The way to do this is using metal flashing around the vent or pipe, sealing joints with appropriate sealants, and installing counterflashing to cover the base flashing. This system is then integrated with the shingles so water is kept out not just at the surface but along the flanges and joints where leaks are most likely to start.

Relying on caulk alone isn’t durable enough to handle temperature changes, UV exposure, and wind-driven rain, so it won’t reliably keep water out over time. Not flashing at all or using a plastic cap without proper sealing also provides clear failure paths for water to penetrate. Using metal flashing with sealant and counterflashing inside the shingle roofing creates a robust, long-lasting weather barrier around penetrations.