Roof flashing is thin material, usually metal, that seals the joints and gaps where the roof surface is interrupted or meets something else. Chimneys, walls, skylights, vents and valleys are the usual places. Flashing is not decorative. It is how a roof handles the spots where plain shingles cannot do the job alone, and it is one of the most common places a leak begins.
Where is flashing used on a roof?
Anywhere two surfaces meet at an angle or something pokes through the roof, water can find a way in. Flashing bridges those joints.
| Location | What the flashing does |
|---|---|
| Valleys | Carries water down the channel where two roof slopes meet |
| Chimneys | Seals the joint between brick or masonry and the roof, usually in several pieces |
| Walls and dormers | Steps along the wall where a roof meets a vertical surface |
| Skylights | Seals around the frame so water flows around it |
| Plumbing and vent pipes | Collars or boots seal around pipes that pass through the deck |
| Eaves and rakes | Drip edge shields the roof edge (what is drip edge) |
| Roof-to-roof transitions | Seals where a low slope meets a steeper one |
Why do leaks start at flashing?
Flashing sits where movement, heat and water concentrate, and it is made from different materials than the shingles around it. A few things go wrong:
- Expansion and contraction. Metal, masonry and wood move at different rates with temperature changes.
- Aging sealants. Caulk and roofing cement dry out, shrink and crack.
- Poor original installation. A missing piece or flashing tucked in the wrong order lets water slip behind it.
- Rust and corrosion. Some metals wear out before the shingles do.
- Storm damage. Wind can lift flashing, and hail can dent or crack soft metals and plastics.
- Debris. Leaves and buildup in valleys and against walls hold water where it should drain.
Our owner has posted about leaks that were hard to track down, including one on a flat roof where water showed up in odd places. Leaks that appear far from where water gets in are a common headache, and flashing details are one of the first places a roofer checks. See how to find a roof leak for the general approach.
What is flashing made from?
Common materials include galvanized steel, aluminum, copper, lead for some pipe boots, and rubber or plastic for pipe collars. Some flashings are bendable and field-formed, while others are made as factory pieces for specific roof features. The best choice depends on the roof, the weather and what the flashing touches. Mixing certain metals can cause corrosion, so a roofer matches materials with care. Manufacturer instructions often specify what they want used with their shingles, and local requirements apply too, which vary by city and county.
What does good flashing work look like?
Water flows over the flashing and shingles in a shingle-like overlap, from the top down. The upper piece overlaps the lower one so water cannot get behind. Sealant is a backup and not the main protection. A well-flashed roof depends on layering, fastening and correct materials more than on caulk. If a repair is mostly a blob of sealant over a joint, ask what is underneath and whether it is a temporary fix.
When can flashing be reused and when is it replaced?
On a replacement, some flashing is replaced with new material, and some pieces may be reused if they are in good shape and compatible with the new roof. Chimney and skylight flashing is often reworked at the same time. Crews can only judge it up close, and the comparison pages on chimney flashing repair vs replace and skylight replace vs reflash cover the trade-offs.
Frequently asked questions
Is flashing the same as drip edge? Drip edge is a form of flashing for the roof's edges. Flashing as a category covers many types around the roof.
Can I fix flashing leaks myself with caulk? Caulk may slow a leak for a time but often hides the underlying problem. It also means getting on the roof, which we do not recommend. Have a roofer look.
How do I know if flashing is failing? From the ground, look for bent, lifted or rusted metal around chimneys, walls and vents. Inside, look for stains near those spots. Do not climb the roof to check.
Does a new roof come with new flashing? Often yes for most pieces, but it depends on the roof and what is reusable. Ask your roofer to list which flashings are replaced on your estimate.
How long does flashing last? It depends on the material, installation and exposure. Some wears out before the shingles do.
Is flashing damage covered by insurance? Policies differ, and cause of loss matters. Read yours and ask your agent.
Talk to us about your roof
Total Roof Protection OKC can inspect your roof's flashing and explain what we see. Call 405-415-5841 to schedule an inspection. An inspection describes your roof and does not predict an insurer's decision.