What Is Roof Flashing? Types, Purpose, and Signs It's Failing
Roof flashing is sheet metal, shaped to fit one specific spot, that keeps water out of a roof where the roof surface meets a wall, chimney, vent pipe, or another roof slope. The International Association of Certified Home Inspectors (InterNACHI) defines flashing as "sheet metal fabricated to a specific shape and designed to prevent water from penetrating the roof system" (InterNACHI). Shingles shed water across open roof areas, and flashing handles the joints and edges where shingles alone cannot.
This guide explains what roof flashing is, what it does, the 7 main types, what it is made of, the signs it is failing, and when flashing needs a roofer instead of a tube of caulk.
Flashing is the waterproofing at roof joints. It is shaped metal that blocks water where shingles meet a wall, chimney, pipe, skylight, or valley (InterNACHI).
Leaks often start at flashing, not at shingles. A 2009 Roofing Contractor technical article estimates that "nearly 90 percent of all roof leaks occur at flashings and penetrations" (Roofing Contractor).
7 common types: step flashing, counterflashing, kick-out flashing, valley flashing, pipe flashing, skylight flashing, and drip edge (Hunker; PNNL).
Corroded flashing needs replacing, not sealing. InterNACHI says flashing that has failed from corrosion should be replaced immediately.
Have a roofer look at suspected flashing leaks. Damage behind siding can stay hidden for years (PNNL).
What Is Roof Flashing?
Roof flashing is thin, rust-resistant metal installed at the joints of a roof to direct water away from places where it could get in. Hunker describes flashing as "a bridge between the shingles and the vertical (or non-roof) elements" of a roof, and notes that most flashing is thin, rust-resistant metal such as galvanized steel or aluminum, though some is rubber or other material (Hunker).
A roof has more joints than most homeowners notice: where a slope meets a wall, around a chimney, around each plumbing vent, where two slopes meet in a valley, at the eaves and rakes, and around skylights. Each joint is a place where water can run behind the roofing material. Flashing covers each one, and you often see only a thin strip of it, or none at all, because flashing may be hidden behind the roof covering (InterNACHI).
What Does Flashing Do on a Roof?
Flashing gives water a path off the roof and keeps it from running behind roofing and siding. Each flashing piece is layered with the shingles so that water moves down and out, over the top of the material below it.
Flashing matters because those joints are where roofs tend to fail. The Roofing Contractor article names "improper termination design, improper workmanship or use of inappropriate materials" as the causes of flashing-related leaks, and calls improper flashing "the single leading contributor to up to three-quarters of all roof failures" (Roofing Contractor). That article is trade press from 2009 and its figures are estimates, so treat them as a rough guide to where leaks start.
Metal flashing also outlasts the common alternative. Hunker puts it plainly: "Flashing is much longer-lasting and far more reliable than any caulked joint" (Hunker).
Types of Roof Flashing
Roof flashing comes in about 7 types, and each one matches a specific part of the roof. The table lists where each goes. Details follow below.
Type | Where it goes | What it does |
Step flashing | Where a sloped roof meets a vertical wall, dormer, or chimney | Overlapping L-shaped pieces carry water down the roof |
Counterflashing | Over the vertical edge of step flashing, such as on a brick chimney | Covers the top edge of the flashing below it |
Kick-out flashing | At the bottom of a roof-to-wall joint, where the eave meets the wall | Diverts water into the gutter |
Valley flashing | Where two roof slopes meet | Forms a channel for water |
Pipe flashing | Around plumbing vent pipes | Seals the opening around the pipe |
Skylight flashing | Around the skylight curb | Seals the head, sill, and sides |
Drip edge | Along roof edges | Guides water into the gutters |
Sources: Hunker; PNNL Building America Solution Center.
Step Flashing
Step flashing is a series of overlapping metal pieces installed where a sloped roof meets a vertical wall. Each piece laps over the one below it, shingle-fashion, so water runs off the roof instead of behind the flashing. The Pacific Northwest National Laboratory's Building America Solution Center, a U.S. Department of Energy resource, says step flashing should extend "at least 4 inches up the wall from the roof deck and at least four inches out along the roof deck" (PNNL).
Counterflashing
Counterflashing covers the vertical part of step flashing where there is no siding to do the job, such as on a brick chimney (Hunker). Step flashing handles the roof side of the joint, and counterflashing handles the wall side.
Kick-Out Flashing
Kick-out flashing, also called a diverter, sits at the lower end of a roof-to-wall joint and sends water into the gutter. PNNL says it "directs rainwater into rain gutters, where it can be carried away from the structure." Without it, heavy rain can overflow at the wall and run down behind the siding. The same page warns that water inside a wall can damage sheathing, framing, and insulation and promote mold, that fiber cement, vinyl, and brick veneer can hide the damage for years, and that an improperly integrated diverter "can do more harm than good" (PNNL).
Valley Flashing
Valley flashing creates a channel for water where two roof slopes meet (Hunker). A valley carries water from two slopes at once, so it is a joint to include in any roof inspection.
Chimney Flashing
Chimney flashing is a combination of the types above. Step flashing runs along the sides of the chimney, and counterflashing covers the masonry edge on a brick chimney (Hunker). A chimney is a large penetration with several sides, which gives water more places to get in.
Pipe Flashing
Pipe flashing, also called boot or jack flashing, is a rubber boot with a metal base that fits around a plumbing vent pipe (Hunker).
Skylight Flashing
Skylight flashing is a set of head, sill, and step pieces around the skylight curb. When a skylight leaks, Hunker says, "it's usually due to improper or failed flashing" rather than the skylight itself (Hunker).
Drip Edge
Drip edge is a metal strip along the roof edges that guides water into the gutters (Hunker). It is the type of flashing most homeowners can see from the ground. Read more in our guide to what a drip edge is and why your roof needs one.
What Is Roof Flashing Made Of?
Galvanized steel is the most common flashing material, followed by lead, copper, and aluminum. InterNACHI describes the materials this way (InterNACHI):
Galvanized steel: the most common flashing material. It is sometimes painted to look like new or aged copper.
Lead: used where flashing must conform to a shape, and on tile roofs because it fits the tile profile.
Copper: seen on high-end homes, especially in coastal areas. InterNACHI lists 16-gauge as the most common and estimates a lifespan of about 70 years, which varies by environment.
Aluminum: possible but uncommon.
Building codes set a minimum for metal flashing. PNNL quotes the 2018 International Residential Code (IRC) section R903.2.1: "the metal shall be corrosion resistant with a thickness of not less than 0.019 inches," which PNNL equates to 26-gauge galvanized sheet (PNNL).
Signs Your Roof Flashing Is Failing
Corrosion, gaps, and water stains near a joint are the main signs of failing flashing. InterNACHI treats corrosion as a graded defect: moderate corrosion can mean replacement is coming soon, severe corrosion needs replacement soon to avoid moisture damage, and flashing that has failed from corrosion should be replaced immediately. Corrosion speed depends on the metal, the flashing quality, and the climate (InterNACHI).
Look for these signs from the ground and from inside the house:
Rust or corrosion on visible metal at the chimney, walls, or vents
Flashing that is bent, lifted, cracked, or pulling away from the roof or wall
Ceiling or wall stains near a chimney, a skylight, or where the roof meets a wall
Sealant or tar patches on a joint, which can mean someone has already tried a fix
Gutters that overflow at a roof-to-wall joint
Because water behind siding can stay hidden for years (PNNL), a clean-looking wall does not prove the flashing above it is working. For a longer checklist, read our guide to signs your roof flashing needs repair and how to tell if a roof leak is coming from flashing damage. If you already see water inside, start with what to do about a leaking roof right away.
Roof Flashing Repair: Patch, Replace, or Call a Roofer?
Flashing repair depends on the damage: a small gap may be repaired, but corroded or badly bent flashing is replaced. InterNACHI's guidance is that flashing which has failed from corrosion should be replaced immediately (InterNACHI). A caulk or tar patch over failed flashing hides the problem for a while, and Hunker's comparison, that flashing outlasts any caulked joint, explains why patches tend not to hold.
Step flashing and kick-out flashing are layered into the shingles and siding, so fixing them often means lifting the surrounding material. That is a job for a roofer, and working on a roof is a fall risk. A temporary fix can buy time during a storm, and our guide to temporary roof leak fix solutions covers short-term options.
Flashing repair belongs with roof repair. When flashing is worn out along with the rest of the roof, it makes sense to ask any contractor whether the existing flashing will be reused or replaced as part of a roof replacement. For a sense of repair costs in New Jersey, see our guide to roof leak repair cost in NJ.
Flashing and Building Code
Building codes require kick-out flashing in some projects. The building department of Hopkins, Minnesota, summarizing IRC section R903.2.1, says kick-out flashing must be at least 2½ inches long and is required "when simultaneously re-siding and re-roofing," but not "when only re-roofing existing buildings" (City of Hopkins). That is a Minnesota city's reading of the model code. New Jersey adopted the 2021 IRC into its Uniform Construction Code with state amendments, effective September 6, 2022 (NJ Department of Community Affairs), so ask your township's construction office which rules apply to your project.
How Hidalgo Brothers Can Help
Hidalgo Brothers LLC provides roof repair, flat roofing systems, roof installation, roof replacement, and roof inspections and maintenance for homeowners in Wharton and throughout Morris County, NJ. A roof inspection is the practical way to find out whether flashing around your chimney, walls, and vents is sound, and storms are a good reason to book one: read why a roof inspection after every major storm catches damage you cannot see from the ground. Overflowing gutters at a roof-to-wall joint also point to the gutter side of the system, which we cover under seamless gutters and gutter repair.
Request an estimate through the Hidalgo Brothers contact page or call (973) 525-6835. Hidalgo Brothers LLC is at 350 W Dewey Ave, Wharton, NJ 07885.
FAQs
What is flashing on a roof?
Flashing on a roof is sheet metal shaped to a specific spot to keep water from entering the roof system (InterNACHI). It goes at joints and openings: walls, chimneys, vent pipes, skylights, valleys, and roof edges.
What is step flashing on a roof?
Step flashing is a series of overlapping L-shaped metal pieces layered into the shingles where a sloped roof meets a wall, dormer, or chimney (Hunker). Each piece laps over the one below it so water runs down the roof and not behind the flashing.
What does kick-out flashing do?
Kick-out flashing directs water from the roof edge into the gutter at the point where the eave meets a wall (PNNL). Without it, water can run down the wall and damage the sheathing, framing, and insulation.
Can you seal roof flashing with caulk?
Caulk can cover a small gap temporarily, but it does not replace working flashing. Hunker states that flashing "is much longer-lasting and far more reliable than any caulked joint" (Hunker). Corroded flashing should be replaced (InterNACHI).
Is drip edge the same as flashing?
Drip edge is one type of flashing. It is a metal strip along the roof edges that guides water into the gutters (Hunker). Other types, such as step flashing and valley flashing, work at different parts of the roof.
Sources
Retrieved October 15, 2026.
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