What Is Flashing in Roofing? Types, Materials, and Costs Explained

Roof flashing is thin metal installed anywhere the roof meets something else. That means chimneys, walls, valleys, skylights and vent pipes. Its job is to steer water away from those seams and down into the gutters.

Shingles do fine on the flat parts of a roof. Trouble starts where the roof gets interrupted. If your shingles look fine and you still have a leak, check the flashing first.

What Does Roof Flashing Do?

Water runs downhill until it hits something. On a roof, that’s a chimney, a dormer wall or a pipe sticking through the deck. Without flashing, water slips into the gap and soaks the decking underneath. Flashing overlaps the shingles like a shingle itself, so water hits the metal and gets carried past the opening.

When flashing fails, the leak rarely shows up right below it. Water runs along the decking and rafters first, then drips somewhere else. That’s why a ceiling stain in the hallway can turn out to be a chimney problem. Our 12 tips for finding and fixing roof leaks shows how to track it down.

8 Types of Roof Flashing

Step Flashing

Step flashing is made of small L-shaped pieces that run up the side of a wall or chimney, one piece per row of shingles. Each piece tucks under the shingle above it and laps over the one below. Water steps down the wall and never gets behind it.

Counter Flashing

Counter flashing caps the step flashing. On a chimney it’s cut into the mortar joints and bent down over the top of the step flashing. Without it, water runs down the brick and slips behind the step flashing.

Valley Flashing

A valley forms where two slopes of the roof meet, and it carries more water than any other part of the roof. Metal valley flashing lines that channel so heavy rain and snowmelt drain off fast instead of soaking into the shingle edges.

Drip Edge

Drip edge is the metal strip along the bottom edges and sides of the roof. It throws water clear of the fascia and into the gutter. Without it, water curls under the shingles and rots the fascia boards. See what a drip edge is for the details.

Chimney Flashing

Chimney flashing isn’t one piece. It’s a set: an apron across the front, step flashing up the sides, counter flashing over the top of that, and a back pan or cricket behind the chimney so water doesn’t pool there. Leave out any one piece and the chimney leaks.

Vent Pipe Flashing

Plumbing vents come through the roof inside a pipe boot, which is a metal base with a rubber collar that seals around the pipe. The rubber dries out and cracks in the sun, often well before the shingles wear out. A cracked boot is one of the cheapest leaks to fix and one of the most common.

Kickout Flashing

Kickout flashing sits at the bottom of a wall where the roof edge stops. It’s a small angled piece that kicks water out into the gutter. Without it, water pours down the side of the house and gets in behind the siding.

Skylight Flashing

Skylights need flashing on all four sides. On the sides it’s usually step flashing, with a head piece at the top and an apron at the bottom. Many skylight kits come with their own flashing kit, and using the right one matters as much as the skylight itself.

Roof Flashing Materials

Aluminum is the most common choice on homes because it’s light, easy to bend and doesn’t rust. Galvanized steel is stronger and costs about the same. According to This Old House, both typically last 20 to 40 years.

Copper costs much more and can last 100 years or longer. You see it on high-end and historic homes. Stainless steel can last over 50 years. Rubber is used only for pipe boot collars, and plastic flashing doesn’t hold up in direct sun.

How Long Does Roof Flashing Last?

Metal flashing can last as long as the roof if it was installed correctly. The weak spots are the sealant and the rubber. Caulk shrinks and pulls away. Rubber boots crack. Freeze-thaw winters speed both up, because water gets into small gaps, freezes and opens them wider.

That’s why the flashing should be replaced along with the shingles. Old flashing that’s bent, rusted or nailed through won’t seal properly against brand new shingles.

Signs Your Roof Flashing Is Failing

From the ground, look for rust streaks, lifted or bent metal, gaps at the chimney and caulk that’s cracked or missing. Inside, look for stains on the ceiling near the chimney, on upper walls under a dormer or around a bathroom vent.

In the attic, check the rafters and decking around each penetration for dark water marks. If the wood around the chimney is stained but the shingles are fine, the flashing is letting water in.

How Much Does Roof Flashing Cost?

National cost guides put an average flashing repair at $200 to $500 and a full flashing replacement at $300 to $1,500, according to This Old House. Chimney flashing repairs often run $600 to $1,500, and valley repairs range from $250 to $2,000, according to RoofingCalc.

What you’ll actually pay depends on the pitch, access, the material and how much wood has rotted underneath. We give you a fixed written price after a free inspection, along with photos of the exact flashing that failed. Book a free roof inspection to get yours.

Can You Repair Flashing Yourself?

You can re-caulk a small gap or reseat a loose piece if you’re comfortable on a ladder. That buys you a season, not a fix. Caulk smeared over rusted or bent flashing just hides the problem until the next freeze.

Replacing step or counter flashing means pulling shingles and sometimes cutting mortar. A mistake there turns a $300 roof repair into a ceiling repair. Leave anything around a chimney or skylight to a roofer.

Flashing on a New Roof: What to Insist On

Ask every roofer who bids your job one question. Will you install new flashing at every chimney, wall, valley and vent, or reuse what’s there? Reusing old flashing saves the roofer time. It doesn’t save you anything if the new roof leaks in two years.

On every Pro Craft roof replacement, new flashing and new pipe boots are already in the price. Walk through our roof installation process to see where each piece goes. After the job, here’s how to tell if your roofer did a good job.

FAQs

What is the purpose of flashing on a roof?

It seals the joints where the roof meets chimneys, walls, valleys and vents. It also sends water away from those openings and into the gutters.

Does flashing go over or under shingles?

Both. Step flashing tucks under the shingle above it and laps over the one below. On a pipe boot, the shingles above overlap the top edge and the bottom edge sits on top of the shingles below.

What is the best material for roof flashing?

Aluminum and galvanized steel suit most homes. Copper lasts the longest but costs far more. Correct installation matters more than the metal you pick.

How do I know if my roof flashing is leaking?

Look for ceiling stains near the chimney, skylights or vents, rust or gaps at the metal, and water marks on the attic wood around each opening.

Should flashing be replaced with a new roof?

Yes. Old flashing won’t seal properly against new shingles. Replacing it during the reroof costs far less than tearing into a new roof later.

What happens if a roof has no flashing?

Water runs straight into the seams at the chimney, walls and vents. It rots the decking and framing and leaks into the house.

How much does it cost to repair roof flashing?

National averages run $200 to $500 for a repair and $300 to $1,500 for full replacement. Chimney work often runs higher.