Flashing — water-shedding detail for roofs and walls

A flashing is a water-shedding building material that redirects water away from joints, penetrations, and transitions in roofs and walls.

Flashing diagram — labeled parts, dimensions, and installation context

What It Is

Flashing is the thin metal or membrane material installed where water is most likely to enter a building assembly. It works by lapping over adjacent materials so water is directed out and down instead of into the structure.

Types

Common types include step flashing, counter flashing, valley flashing, kickout flashing, drip edge flashing, and vent or window flashing. Different details are used for roofing, siding, and masonry.

Where It Is Used

Flashing is used around chimneys, roof valleys, skylights, vents, windows, doors, decks, and roof edges. Anywhere two surfaces meet, flashing is usually part of the water-management detail.

How to Identify One

Look for thin metal edges or hidden membrane layers at transitions and penetrations. Rust, open gaps, and caulk-only repairs are clues the original flashing may be missing or failing.

Replacement

Replace flashing when it corrodes through, comes loose, was installed in the wrong sequence, or was omitted entirely. Proper repair often requires selective tear-off around the problem area.

Flashing — FAQ

What does a flashing do?

It redirects water away from joints, penetrations, and transitions in roofs and walls. In a home, that helps the surrounding system work the way it should.

How can I tell if a flashing needs attention?

Water stains near chimneys or roof intersections are a major clue. Loose metal, rust, and sealant-heavy repairs are other common warning signs.

Can I replace a flashing myself?

Some exposed flashing repairs are DIY-friendly, but many critical details are buried and easy to get wrong. Proper overlap matters more than surface caulk.

How much does flashing repair or replacement cost?

A small piece of flashing is cheap, but access and surrounding tear-off often dominate the price. Costs rise when roofing, siding, or hidden rot also need repair.