What is the purpose of flashing on a roof?

• A. To seal joints in the gutter.
• B. To promote ventilation in the attic.
• C. To prevent seepage of water into a building around any intersection or projection in a roof.
• D. To help attach shingles to the roof deck.

Answer: (C)

Flashing is a waterproofing detail placed at roof joints and around any projections to keep water from entering the building. By lining intersections where two roof planes meet, or where the roof meets chimneys, vents, skylights, or walls, flashing directs water to shed away from the interior. It creates a sealed barrier that accommodates movement from temperature changes and wind, so rain doesn’t find gaps to seep through.

This is different from sealing gutters, which handle water that’s collected along the eaves, or from attic ventilation, which is about improving air flow. It’s also not about attaching shingles; nails secure shingles, while flashing sits at the joints to prevent leaks.