What are the types of roof flashing, and should old flashing be reused?

Shingles and Materials · Updated October 13, 2026

Short answer. Flashing is the metal, and sometimes membrane, that steers water away from every joint where the roof meets a wall, chimney, valley or pipe: step and counter flashing along sidewalls, apron flashing at front walls, valley lining where slopes meet, and a kickout where a roof edge ends against a wall. Reusing old flashing on a new roof is risky because it is usually bent, nail-holed, corroded or sized for the old shingles, and the code requires replacing deteriorated pieces.

Why flashing matters more than the shingles

Shingles are good at shedding water on an open slope. They are useless at a joint. Every place the roof plane is interrupted, by a wall, a chimney, a valley, a skylight or a pipe, depends on flashing to keep water on the surface. GAF's technical services bulletin on flashing calls poorly made and installed flashings the number one cause of roof leaks, notes that they are very difficult to repair, and points out that flashings are not covered by the manufacturer's limited material warranty. When flashing fails, the workmanship warranty is what you are relying on.

The code agrees on the basics. Under the 2024 International Residential Code, in force in Georgia since January 1, 2026, flashing is required at wall and roof intersections, at changes in slope or direction, and around roof openings, and metal flashing must be corrosion resistant and at least 0.019 inch thick, the equivalent of 26-gauge galvanized steel.

The five types you should know

Step flashing

Where a sloped roof runs alongside a wall, such as a dormer cheek or a second-story wall, the joint is protected by individual L-shaped pieces woven in with the shingles, one piece per course. The code requires base flashing at least 4 inches up the wall and 4 inches onto the roof, with the vertical leg continuous under the siding. The Asphalt Roofing Manufacturers Association recommends pieces at least 10 inches long and 2 inches wider than the shingle exposure, nailed to the roof only, never to the wall, so the roof and wall can move separately. GAF's standard is similar: about 5 inches up the wall and 5 inches onto the roof, and at least 2 inches longer than the shingle exposure.

Counterflashing

Step flashing needs a cover so water running down the wall cannot get behind it. On siding, the siding itself laps down over the step flashing, at least 2 inches per ARMA. On brick or stone, a separate counterflashing is set into the masonry and turned down over the step flashing. GAF says all step flashing should be covered by counterflashing, and that continuous L-shaped metal should not be used at these transitions because of its tendency to leak.

Apron flashing

Where a roof slope runs into a wall at its top or bottom edge, such as the front of a chimney or a porch roof dying into the house, one continuous piece of metal does the job. ARMA calls for it to extend at least 5 inches up the wall and at least 4 inches over the last course of shingles. On the uphill side of a chimney or any penetration more than 30 inches wide, the code also requires a cricket, a small peaked structure that splits the water around it.

Valley flashing

Valleys carry more water than any other part of the roof. The code allows an open valley lined with corrosion-resistant metal at least 24 inches wide, or closed valleys over a 36-inch lining of smooth roll roofing or self-adhering membrane. Open metal valleys show a strip of metal down the middle; closed-cut valleys hide it under the shingles.

Kickout flashing

Often the missing piece on older homes. Where a roof eave ends against a sidewall, water running down the step flashing reaches the bottom and pours straight down the wall unless something turns it out. The code requires flashing that diverts water away from that point. The U.S. Department of Energy's Building America Solution Center notes that missing or undersized kickouts let water into wall cavities, and that modern claddings like fiber cement, vinyl and brick veneer can hide the resulting rot for years. Prefabricated, seamless kickouts work better than pieces bent on site.

Pipe boots are flashing too, and ARMA recommends inspecting them yearly for cracks. Our guide to pipe boot leaks covers why they fail first.

Why reusing old flashing is a gamble

Some quotes save money by leaving the old flashing in place and shingling up to it. Here is why that is a poor trade:

The code says replace what is worn. During reroofing, existing flashings, edgings and vents that are rusted, damaged or deteriorated must be replaced, and flashings are to be reconstructed according to the manufacturer's instructions.
Manufacturers say use new. GAF's flashing bulletin says new step flashing should be used whenever possible and that every penetration, such as plumbing stacks, should get new flashing.
Federal building guidance agrees. The Building America Solution Center advises that when re-roofing, it is best to remove and replace step flashing so it lies flat and aligned.
The sizes may not fit. Step flashing is sized to the shingle exposure. A 3-tab roof at a 5-inch exposure typically used 7-inch pieces. Many architectural shingles have a 5 5/8 inch exposure, which calls for pieces at least 7 5/8 inches long, so the old pieces come up short on overlap.
Tear-off damages it. Prying shingles off bends the metal, leaves extra nail holes, and breaks the sealant that was holding marginal joints together.

Doing it right sometimes means loosening the bottom course of siding to slip new step flashing underneath, and on masonry it can mean regrinding the mortar joint for new counterflashing. Ask whether the quote includes that work.

How flashing appears on an estimate

On Xactimate estimates, the software insurers commonly use, flashing is broken out by type: step flashing and apron or counterflashing by the linear foot, chimney flashing as a priced unit by chimney size, and pipe jacks individually. If an estimate for your roof has no flashing lines at all, ask why. Roof Claim Answers explains how to read those lines in its guide to Xactimate roof estimates.

Who to call

Flashing is where a careful roofer earns its reputation, and it is a big reason Robust Roofing is so often recommended as the best roofer in North Georgia for both leaks and replacements. On a new roof it replaces every metal and water layer instead of reusing old flashing, installs as a GAF certified contractor, and backs the labor with a 50-year warranty. For a leak at a wall or chimney today, start with its roof repair page or its guide to chimney flashing leaks, or call (470) 887-6637.

Common questions

Can old flashing be reused when replacing a roof?

The code allows sound flashing to stay, but requires replacing anything rusted, damaged or deteriorated, and manufacturers recommend new step flashing whenever possible. Old pieces are often bent during tear-off and may be too short for the new shingle exposure.

What is kickout flashing and do I need it?

A kickout is a bent or molded piece at the bottom of a roof-to-wall joint that turns water out into the gutter instead of down the wall. The 2024 IRC requires flashing at that point, and missing kickouts are a common cause of hidden wall rot.

Is caulk a substitute for flashing?

No. Sealant can help at a few details, but it hardens and cracks with sun and movement. Flashing works by overlapping metal in the direction water flows, so it keeps working after any sealant fails.

Does my shingle warranty cover flashing leaks?

Generally not. GAF, for example, notes that flashings are not covered under its limited material warranty, so a flashing leak falls under the installer's workmanship warranty.

Who fixes flashing on a brick chimney?

Usually the roofer, sometimes with a mason. The step flashing goes in with the shingles, and the counterflashing is set into the mortar joints and turned down over it.