Roof Flashing Types: Where Each One Goes and What It Does

Roof flashing is thin metal (or sometimes a flexible membrane) that sends water away from the spots where a roof meets a wall, a pipe, a chimney or its own edge. The main types are step, base, counter, apron (continuous), drip edge, valley, kickout, and the collars and curbs around vents, chimneys and skylights. Each one solves a different joint, and most leaks start at one of those joints, not in the middle of the shingles.

TL;DR

• Step flashing is a series of small bent pieces woven into shingle courses where a sloped roof meets a vertical wall.
• Counter flashing is the top layer. It covers the upper edge of step or base flashing, usually at a chimney or masonry wall.
• Apron (continuous) flashing is one long piece. Drip edge is a different part that protects the roof edge and fascia.
• Match the metal to the roof and the climate. Galvanized steel is common, while copper and aluminum last longer.
• Flashing problems often look like “mystery” leaks. A free inspection can find the failed joint before the ceiling stains show up.

Table of Contents

• What flashing does and where it is required
• The main roof flashing types
• Quick comparison table
• Common mix-ups, settled
• Choosing flashing material
• Signs your flashing needs attention
• Get your flashing checked in Baytown
• FAQ
• Sources

What flashing does and where it is required

The asphalt roofing industry’s residential manual describes flashing as thin sheet metal placed between roofing components and a wall or protrusion so water runs toward gutters and drains and away from the building interior. Shingles shed water on open slopes. They can’t do that at a joint, a gap or a hole, so metal fills the job there.

The 2018 International Residential Code, the model code many US jurisdictions build on, calls for flashing at roof-wall intersections, around skylights and other roof openings, at roof penetrations, and wherever the roof changes slope or direction. It also says the flashing must be integrated with the roof covering and underlayment to form a watertight assembly. Local codes can differ, so your roofer or building department has the final word for your address.

That list is also a map of where leaks start. Walls, chimneys, pipes, valleys and skylights all need flashing, and each needs a slightly different shape.

The main roof flashing types

Step flashing

Step flashing is where a sloped roof runs into a vertical wall, such as the side of a dormer or a second-story wall. Small rectangular pieces, each bent at 90 degrees, are installed in layers with the shingles. IKO describes it as pieces installed in layers with shingles along roof-to-wall joints. Each shingle course gets its own piece, so water that gets behind one shingle lands on the metal below and is passed down to the next course.

The EPA-backed Building America Solution Center says step flashing is typically preformed, with 5-inch legs and a 7-inch length, often called 5 by 7 step flashing. The 2018 IRC sets a floor for asphalt shingle roofs: base flashing against a vertical sidewall must be continuous or step flashing at least 4 inches high against the wall and 4 inches wide above the underlayment.

Base flashing

Base flashing is the bottom layer in a two-part system. IKO identifies it as the bottom piece in two-part flashing, for example at chimneys that need two pieces. Step flashing often serves as the base flashing on a sloped roof. On low-slope and flat roofs, base flashing is usually a formed or membrane piece turned up the wall or curb.

Counter flashing

Counter flashing is the cover. The Insurance Institute for Business & Home Safety defines it as formed metal secured on or into a wall, curb, pipe or rooftop unit to cover and protect the upper edge of base flashing and its fasteners. It is typically the top part of a two-piece assembly that laps over a base flashing whose fastening is independent.

You see it at chimneys, parapet walls, and the edges of rooftop equipment. Water that runs down the wall hits the counter flashing, drops onto the base flashing, and runs out onto the roof.

Apron (continuous) flashing

Apron flashing is one long piece, not a stack of small ones. IKO describes continuous, or apron, flashing as a long single piece of metal that carries water down onto the shingles below. You find it at the bottom of a chimney, below a dormer wall, or where a roof slope butts into a wall at the bottom edge. On metal or rubber membrane roofs, continuous flashing is also used in place of step flashing.

Drip edge

Drip edge runs along the eaves and rakes, not at a wall. This Old House describes it as angled metal along roof edges that redirects water away from the eaves and into gutters, which helps protect the fascia. The Building America Solution Center adds that this L-shaped metal also helps keep rain, wind and wildfire embers out of the gap between roofing and fascia board.

For high-wind areas, the same program recommends drip edge at eaves and rakes, overlapped at least 3 inches and fastened at no more than 4 inch spacing. That matters on the Gulf Coast, where wind-driven rain is part of the job description. If you have ever wondered how drip edge differs from a gutter apron, our guide to drip edge vs. gutter apron covers it.

Valley flashing

A valley is where two roof slopes meet and funnel water. It carries more water than any other part of the roof. The Department of Energy’s building science education site advises peel-and-stick membrane in valleys and roof-wall intersections, then metal flashing over the membrane, integrated with the shingles. Valley leaks are common and often get blamed on the wrong spot, so see our page on roof valley leaks for the usual causes.

Vent pipe, chimney and skylight flashing

Anything that sticks up through the roof needs its own collar, boot or curb flashing: plumbing vents, flue stacks, chimneys, skylights, even solar mounting brackets. When a roof is redone or a new penetration is added, the Building America Solution Center says to inspect and add or replace flashing and sealing around every penetration to keep a continuous water control layer.

Chimneys are the most complex case, because they combine step flashing on the sides, an apron at the bottom, and counter flashing set into the masonry. A roof leak around a chimney usually traces back to one of those layers.

Kickout flashing

Kickout (diverter) flashing sits at the lower end of a roof-wall joint, where the step flashing ends at the eave. It turns runoff into the gutter instead of letting it run down behind the siding. The Building America Solution Center recommends it at the eaves of roof-wall intersections, especially in hurricane-prone, heavy-rain regions. A missing kickout is a classic cause of rotted wall sheathing that shows up years later.

Quick comparison table

Common mix-ups, settled

Step flashing vs. counter flashing

They work as a pair, not as alternatives. At a chimney, This Old House explains that step flashing is woven into the shingle courses as the first layer, while counterflashing is embedded in the chimney’s mortar joints and folded down to cover the top of the step flashing. Step flashing belongs to the roof. Counter flashing belongs to the wall or masonry.

There is a practical reason for the split. Where the chimney and roof can move differently, the residential manual says to use apron flashings fastened to the roof deck and counter flashings fastened to the masonry so the counter flashing slides over the apron without affecting water runoff. IKO notes the same benefit of two-part flashing: the base and counter pieces can move with the roof material as it expands and contracts.

Step flashing vs. apron flashing

Step flashing runs up the side of a wall along the slope. Apron flashing runs along the bottom of a wall or chimney, across the slope. One is many small pieces that follow the shingle courses, and the other is a single long piece. On a chimney you will usually see both, with counter flashing over them.

Drip edge vs. flashing

Drip edge is technically a type of flashing, but it does a different job. Wall and penetration flashing seals joints in the middle of the roof. Drip edge guards the perimeter, so water leaves the roof over the gutter instead of curling back onto the fascia. A roof can have perfect wall flashing and still rot at the eaves without drip edge, and the reverse is also true.

Choosing flashing material

This Old House says material choice depends on roof type, pitch, budget, looks and regional climate. Its summary of options:

• Galvanized steel: the most common and cheapest, but the least durable of the metals.
• Aluminum: among the longest lasting. It and galvanized steel are listed at roughly 20 to 40 years.
• Copper: highly corrosion resistant, and it can last 100 years or longer.
• Lead: very long lived, but rarely used now because of health and environmental concerns.

Roofing Elements Magazine notes that galvanized steel is often used on asphalt shingle roofs and should be G-90 galvanizing or better to resist rust. In regions with salt air, chemical exposure or high rainfall, it says aluminum, copper, stainless steel or silicone-based flashings may be better options. Baytown sits on the upper Texas Gulf Coast with humid air and heavy rain, so that is worth weighing for your own roof.

Two more rules save money. First, IKO says plain aluminum reacts with alkaline surfaces like concrete and masonry, so it must be coated there, and coated near the coast too. Second, the Journal of Light Construction advises flashing material that is at least as durable as the roof covering. Thin aluminum on a roof meant to last decades makes little sense, and a longer-lived metal can lower life-cycle cost because flashing is expensive to redo.

Flexible options exist as well. Roofing Elements Magazine explains that EPDM, PVC and butyl-based flashings suit irregular shapes or areas that move or vibrate. On a flat or low-slope commercial roof, membrane flashing is the norm alongside the roofing system itself.

Signs your flashing needs attention

You rarely see flashing fail directly. You see what it lets through:

• Brown stains on a ceiling or wall near a chimney, dormer, skylight or vent.
• Staining or peeling paint on siding below a roof-wall joint, a common sign of a missing kickout.
• Rust, gaps, lifted edges or old caulk smeared over a joint.
• Shingles curling or missing along walls and edges after a storm.
• Damp attic wood or insulation on one side of the house only.

Caulk or roofing cement alone is a temporary patch, not a flashing system. If you see those signs, get a roofer to look at the joint before the decking underneath is soaked. Our guide to roof flashing repair covers causes and when repair makes sense. After a hailstorm or high winds, damaged flashing is often part of a covered loss, which is where insurance claim help comes in.

Our view on flashing

Most of the roofs we’re called to look at don’t need a new roof. They need the right piece of metal in the right place. A failed chimney apron, a missing kickout or a rusted pipe boot is a repair, and we say so.

We photograph the problem joint so you can see what we see, and we explain the options plainly. If the roof is near the end of its life, we walk you through that honestly too, including how the claim paperwork works when storm damage is involved. Flashing is cheap compared with the water damage it prevents, so we think it deserves the same care as the shingles.

Get your flashing checked in Baytown

If any of those signs sound familiar, we offer free, no-obligation inspections for homes and commercial buildings in Baytown and nearby communities. We check every flashing joint, show you photos, and recommend repair when repair will do. See our roof repair services or book a roof inspection.

Active leak during a storm? Our emergency roof repair team is available seven days a week.

FAQ

Is counter flashing the same as continuous flashing?

Not exactly, although some guides use the terms loosely. Counter flashing is defined by its job: it covers the top edge of base flashing. Continuous flashing is defined by its shape: one long piece. A continuous piece can serve as base flashing, and a separate counter flashing then covers it.

Do I need drip edge if I have flashing everywhere else?

Yes, in most cases. Drip edge protects the eaves and rakes, which wall and chimney flashing never touch. The 2018 IRC flashing rules focus on walls, openings, penetrations and slope changes, so check your local code and ask your roofer whether drip edge applies to your roof.

How long does roof flashing last?

It depends on the metal. This Old House puts aluminum and galvanized steel at about 20 to 40 years and copper at 100 years or more. Exposure, installation quality and movement of the roof also affect the real lifespan.

Can flashing be repaired without replacing the roof?

Often, yes. Many flashing failures are local: a rusted collar, a lifted apron or a missing kickout. A roofer can replace the failed piece and reintegrate it with the surrounding shingles. If the shingles around it are also worn out, replacement may be the better value, and an inspection will show which case you have.

Which flashing type is used at a chimney?

Usually all of the layered types together: step flashing on the sides, an apron at the front, and counter flashing set into the masonry on top. Where the chimney and roof can move independently, the apron and counter pieces are fastened separately so they can slide against each other.

Sources

• Residential asphalt roofing manual, flashing chapter
• IRC 2018 R903.2 flashing requirements
• What is Roof Flashing? IKO North America
• Flashing of Roof-Wall Intersections in Existing Homes, Building America Solution Center
• Metal Flashing guidance, IBHS
• Leakproof Flashing, This Old House
• What Is Roof Flashing? This Old House
• Look for Missing Roof and Wall Flashing, Building America Solution Center
• Roof Edge Protection, Building America Solution Center
• Moisture Barrier and Flashing on the Roof, Building Science Education
• Flashing of Penetrations in Existing Roofs, Building America Solution Center
• The Complete Guide to Roof Flashing, Roofing Elements Magazine
• JLC Field Guide: Flashing

Recommended

• Roof Flashing Repair: Causes, Costs and When to Call a Pro
• Drip Edge vs. Gutter Apron: What Each One Does