Roof Flashing Types: Where Each Goes and What It Does

Step, counter, base, valley, drip edge and chimney flashing explained, plus copper vs aluminum vs galvanized and what matters on Tampa Bay roofs.

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Roof Flashing Types: Where Each Goes and What It Does

Roof Flashing Types: Where Each Goes and What It Does

Layered flashing around a brick chimney

💬 Hi, I’m the Hytz Roofing assistant. Short answer: roof flashing is thin metal (or plastic or membrane) that seals the spots where water likes to sneak in. The main types are step, continuous (L-shaped), counter, base, kick-out, valley, vent pipe, skylight, chimney and drip edge flashing. Each one belongs in a specific place, and a leak usually means the wrong type, a worn one, or a poorly installed one. Below, I’ll show you where each goes, how step flashing and counter flashing differ, how drip edge fits in, and which metal to pick for a Florida roof.

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TL;DR

  • Flashing protects roof edges, walls, chimneys, vents and valleys, where roofs leak most often.
  • Step flashing runs along a sidewall under the shingles. Counter flashing sits over the top of other flashing to cover the joint.
  • Drip edge is a flashing type for roof edges. It guides water into the gutter and away from the fascia.
  • Copper lasts longest, aluminum is light and affordable but needs care near salt air, and galvanized steel is the most common and least durable.
  • Leak or flashing repair on our roof repair page is published at $350 to $900.

Table of Contents

What roof flashing does 🛠️

Flashing is a thin strip of sheet metal or plastic installed around roof features such as chimneys, vents and flue pipes. It redirects water away and creates a watertight seal around penetrations and transitions. It can be made from metal, plastic or self-adhering membrane that meets building code.

Why it matters: roofs usually leak at transitions and penetrations, not in the open field of shingles. A roof can have perfect shingles and still drip into your living room because of a $20 piece of metal that failed.

Flashing is used in three kinds of places:

  1. Where a roof meets a wall.
  2. Where one roof plane meets another.
  3. Where something pokes through the roof, like a plumbing vent.

The main roof flashing types

Step flashing

Step flashing is a series of small right-angle metal pieces. One half sits behind the house wrap on the wall, and the other half is woven in with or under the shingles of the roof. You see it where a sloped shingle roof runs into a vertical wall, like a dormer side or a second-story wall over a porch roof.

Each piece overlaps the one below it, like a staircase. Water that gets past one shingle lands on the metal and runs down to the next course instead of soaking into the wall. BSC Information Sheet 303 describes it as moving the wall’s drainage plane onto the roof’s drainage plane.

Continuous (L-shaped) sidewall flashing

Continuous flashing is one long L-shaped piece instead of many small ones. Fine Homebuilding notes it is an alternative to step flashing that building code permits. The Building America Solution Center says either continuous L-metal or step flashing is used at roof-wall intersections, depending on roof type. On asphalt shingle roofs, step flashing is the usual choice.

Kick-out (diverter) flashing

Kick-out flashing sits at the bottom of a roof-to-wall joint, where the roof edge meets the sidewall. It diverts water away from the wall and into the gutter. That page lists kick-outs as required in several IRC editions and in the 2020 Florida Residential Code.

This little piece is often missing. Without it, all the water running down the step flashing hits the siding at one spot. The same source warns that a diverter that is undersized or not tied into the wall’s water barrier can let water into the wall cavity and cause damage and mold. Size and integration matter.

Base flashing and counter flashing

Base flashing sits at the bottom of a vertical surface and ties into the roof. Counter flashing (also called cap flashing) is the upper piece that laps over it. Together they make a two-part seal. We cover the difference in detail in the next section.

Chimney flashing

A chimney needs several pieces working as a system. The Building America Solution Center describes base flashing, step flashing and counterflashing. Base flashing handles the transition at the brick. Step flashing is layered with the roofing along the sides. Counterflashing is set into the mortar joints and laps over the others.

For wider chimneys, there is one more piece: a cricket. JLC says best practice is to use a cricket to divert water away from the upper edge of the chimney. It is a small peaked saddle behind the chimney that splits the water flow.

Valley flashing

A valley is where two roof slopes meet in a V. All the water from both planes runs down that line, so it is one of the highest-flow areas on your roof. Valley flashing is a metal channel (or a woven or cut shingle detail with underlayment) that carries the flow to the eave. A bad valley will leak during heavy Tampa Bay summer downpours.

Vent pipe flashing

Every plumbing vent pipe that comes through your roof has a flashing collar or boot. It is a flat base that sits under the upslope shingles, with a cone or sleeve around the pipe. Rubber collars wear out from sun exposure before the roof does. If you suspect one, see our guide to plumbing vent leak clues you can check safely.

Skylight and headwall flashing

Skylights are usually flashed with a kit made for the unit: sill, side and head pieces that overlap in order. Headwall flashing is the piece along the top of a wall that sits at the lower end of a roof slope, such as a dormer front. Both are common leak sources because several joints meet in a small space.

Drip edge

Drip edge is a metal strip along the eaves and rakes. It sends water off the roof edge into the gutter and keeps it from wicking back onto the fascia and decking.

Flat roof flashing

On low-slope and commercial roofs, flashing shows up at parapet walls, curbs, edges and drains. Parapets are a big one. Our post on parapet wall flashing parts and fixes walks through them. For rooftop units, see HVAC curb leak checks.

Quick reference table 📋

Flashing type Where it goes What it does
Step flashing Sloped roof meets a vertical wall Layers with shingles to shed water off the wall joint
Continuous (L) flashing Same wall joint, one long piece Alternative to step flashing where code permits
Kick-out Bottom end of a roof-wall joint Sends water into the gutter, not behind siding
Base flashing Bottom of a vertical surface Ties the wall or curb to the roof surface
Counter flashing Over the top of base or step flashing Covers the joint so water can’t get behind
Chimney flashing All four sides of a chimney, plus cricket Seals the brick-to-roof transition
Valley flashing Where two slopes meet Carries heavy water flow to the eave
Vent pipe flashing Around pipes through the roof Seals the penetration
Skylight flashing Around the skylight frame Seals the frame on all sides
Drip edge Eaves and rakes Guides water into the gutter

Step flashing vs. counter flashing

They do different jobs, and they often work together.

Step flashing is made of many small pieces woven in with shingles. It is built to handle a sloped roof running along a wall.

Counter flashing is one piece (or a run) that covers the top edge of another flashing. It prevents water from running behind it. On a chimney, it’s set into the mortar. On a flat roof wall, it’s tucked into a reglet or fastened to the wall, then sealed.

One rule from JLC is worth knowing: don’t fasten a flashing to both the chimney and the roof. The base flashing attaches to the roof only, and the counterflashing to the chimney only, so each can move on its own. Fastening both ties them together and tends to tear the seal when the house shifts or heats up.

Rule of thumb: step flashing is for sloped roofs along walls. Counter flashing is the cover piece that finishes a base or step flashing detail.

Step and counterflashing positions and roles

Drip edge vs. flashing

Drip edge is flashing. It just lives at a different spot. Wall and penetration flashing handles joints and holes. Drip edge handles the roof perimeter.

So you don’t choose one or the other. A good roof has both. If your estimate lists drip edge, step flashing and pipe boots as separate line items, that’s normal. Our guide to reading roofing estimate line items shows how to spot them.

Flashing materials: copper vs. aluminum vs. galvanized steel

The metal matters as much as the type.

Material Strengths Watch for
Copper Highly corrosion-resistant and long-lasting, develops a green patina Higher cost; don’t let it touch other metals in wet spots
Aluminum Durable and lightweight Can corrode if left unpainted and exposed to salty air or masonry materials
Galvanized steel Most common, easy to find Least durable: the zinc coating wears away, and masonry or pressure-treated wood speeds that up

The same source flags galvanic corrosion when different metals touch in a wet location. So match metals. Don’t put aluminum against copper, or use steel nails on aluminum flashing.

Code sets minimum thickness. As examples, the Los Angeles City standard lists 0.024 inch for aluminum, 26 gage G90 galvanized steel and 16 oz copper. Oregon’s residential code sets a floor of 0.019 inch for corrosion-resistant flashing metal and calls for sidewall step flashing at least 4 inches high and 4 inches wide. Those are other states’ codes, so your local building department and the roofing manufacturer’s instructions set the rule for your Florida roof.

Flashing on Tampa Bay roofs 🌴

Tampa Bay roofs deal with hard rain, strong wind, sun and salt air near the coast. That affects flashing choices in a few ways:

  • Salt air: aluminum left unpainted near the water is the case that This Old House warns about. Painted or coated metal, or copper, is worth asking about for waterfront homes.
  • Kick-outs: the 2020 Florida Residential Code is among the editions listed as requiring them, so a sidewall without one deserves a look.
  • Wind-driven rain: water can move sideways and uphill under laps, so overlap and sealing details matter at walls, valleys and penetrations.
  • Metal roofs: flashing and trim details count on coastal metal roofs. See our post on coastal Florida metal roofs for what to ask for in a contract.
  • Tile roofs: flashing under and around tile is often metal or membrane, and it may outlast or underperform the tile. It is worth checking at any tile roof inspection.

If you’re planning a shingle replacement, flashing should be part of the plan, not an afterthought. Our asphalt shingles page explains how we install them.

Our perspective

We see the same thing on Tampa Bay roofs again and again. The shingles look fine, but the leak is at a wall joint, a pipe boot or a chimney. Flashing is small, cheap next to the roof, and it decides whether a roof keeps water out.

That’s why we treat flashing as its own line of work, not a throw-in. When we replace a roof, we plan every wall, valley and penetration, and we use details that fit the roof material and the manufacturer’s requirements. As a GAF Master Elite® Contractor, we install to manufacturer standards, and our work is backed by manufacturer warranties.

Our advice: ask what flashing is going on each joint, what metal it is, and how it’s tied in. A clear, itemized answer is a good sign. We provide itemized estimates so you can see it.

Anthony

Signs your flashing is failing 🚨

  • Water stains on the ceiling near a wall, chimney or vent.
  • Rust, gaps or lifted metal at wall joints.
  • Dried, cracked sealant or caulk bunched along flashing. Caulk alone is a short-term patch.
  • Stains on siding below a roof edge, which can point to a missing kick-out.
  • Cracked pipe boots.

If water is coming in now, follow our 6 emergency steps for a roof leak in rain. Stay off the roof when it’s wet. Small flashing repairs are often the fix, and our published range for roof leak and flashing repair is $350 to $900. Chimneys, skylights and large wall runs can need more work, so we inspect first and give you an itemized estimate.

Get your flashing checked 💬

Not sure which flashing you have, or whether it’s the source of a leak? We can look at it. We handle roof leak and flashing repair and certified roof inspections across Tampa Bay and Central Florida. We’re licensed (Florida Contractor License #CCC1332551) and insured, and we can help with insurance claims if storm damage is involved.

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If you’re deciding between repair and a full roof replacement, our roof replacement cost guide lays out the numbers. Ready to talk? Request an estimate from Hytz Roofing.

FAQ

What are the most common types of roof flashing?

Step flashing, counter flashing, valley flashing, vent pipe flashing, chimney flashing, skylight flashing and drip edge are the ones most homes have. Kick-out flashing is a small but important piece at the bottom of roof-wall joints. Flat roofs add base, edge and parapet flashing.

What is the difference between step flashing and counter flashing?

Step flashing is a series of overlapping pieces woven into shingles along a sloped roof-wall joint. Counter flashing is a cover piece that laps over the top of base or step flashing so water can’t get behind it. On chimneys, both are used together.

Is drip edge the same as flashing?

Drip edge is a type of flashing placed along the eaves and rakes. It guides water off the roof into the gutter. It doesn’t replace wall, valley or vent flashing, which seal different spots.

Which is better, copper or aluminum flashing?

Copper is more corrosion-resistant and longer-lasting, but costs more. Aluminum is durable and lighter, and should be painted or coated near salty air. Avoid putting dissimilar metals in contact in wet spots, since that can cause galvanic corrosion.

Can flashing be repaired without replacing the roof?

Often, yes. Many flashing problems are local, like a worn pipe boot, a lifted sidewall piece or a missing kick-out. A roofer should inspect the surrounding shingles and underlayment too, since water may have been getting in for a while.

Sources