Types of roof flashing and how they work

Roof flashing directs water around the places where a roof cannot be one uninterrupted surface. It protects the edges, walls, valleys, chimneys and openings that shingles alone cannot handle.

When you replace a roof, the flashing deserves its own conversation. Two proposals can name the same shingle while including very different work around a chimney or behind siding. Ask which flashing will be replaced, which will remain and how the contractor will connect it to the roof and wall materials.

For the broader budget, see our roof replacement cost guide. This article explains the flashing details that help define that scope.

How flashing keeps water moving out

Think about overlapping roof shingles: water runs from an upper layer onto the surface below it. Many flashing details use that same drainage principle. Their overlaps should carry water outward and downhill instead of directing it behind the roof or siding. [1]

Flashing can include formed metal, flexible boots and membranes. It must fit the roofing system and connect to the surrounding materials. A well-made piece installed in the wrong place, or with the wrong overlap, can still let water in.

Sealants have a role where the product’s instructions call for them. They should not be used to improvise a missing drainage detail. For example, a correctly integrated wall flashing can direct water out even when water gets behind the siding. [1]

Common roof flashing types

Type	Where it goes	What it does
Step flashing	Along a sloped roof where it meets a sidewall or chimney	Overlapping pieces carry water onto the roof surface
Apron or headwall flashing	Where a roof meets the face of a wall or the downhill face of a chimney	Bridges the transition and directs water onto the roofing below
Counterflashing	Above base or step flashing, often at masonry chimneys	Covers the upper edge of the lower flashing
Kickout flashing	At the bottom of a roof-to-wall intersection	Diverts concentrated runoff away from the wall and toward the gutter
Valley flashing	Where two roof slopes meet in an open valley	Forms a protected path for concentrated runoff
Drip edge	Along eaves and rake edges	Directs water off the roof edge and helps protect the wood beneath
Pipe boot flashing	Around plumbing vent pipes and similar penetrations	Seals the pipe opening while tying into the roof covering
Skylight flashing	Around a skylight or its raised curb	Connects the opening to the surrounding roofing and drainage layers

The details below describe typical residential applications. Metal roofs, tile roofs and membrane roofs can require different systems from asphalt shingles. Installation must follow the selected products and applicable requirements. [1, 2, 3, 4, 5]

Step flashing

On an asphalt-shingle roof, step flashing is usually a series of bent metal pieces installed with successive shingle courses along a wall. Each piece overlaps the one below it, so water is repeatedly directed back onto the roof. The wall side must connect correctly with the wall’s drainage layer and siding. [1]

Most of the detail is concealed. Seeing metal along the wall does not establish that the pieces overlap correctly or extend where they need to. During replacement, ask whether access behind the siding is included if the existing detail needs correction.

Apron flashing and counterflashing

Apron flashing handles a transition such as the downhill face of a chimney or a roof running into a wall. Counterflashing protects the upper edge of the lower flashing. At a masonry chimney, it is commonly integrated into the masonry joint above, overlapping the roof flashing below. [2, 6]

This two-part arrangement also accommodates movement between the roof and chimney. A bead of sealant applied across an exposed joint does not demonstrate that the underlying assembly is properly flashed. [2]

Ask the contractor to explain the whole chimney detail. “Chimney flashing included” should identify the sides being addressed and whether the work includes the connection to the masonry.

Kickout flashing

Kickout flashing is the small diverter at the bottom of a roof-to-wall junction. It turns runoff away from the wall and toward the gutter. Without an effective diverter, concentrated water can repeatedly wash the siding and enter the wall assembly. [7]

It is easy to overlook because it is a small component. If a gutter, roof edge and wall meet in the same spot, ask how that junction will drain. Adding a gutter alone does not answer the flashing question. See missing kickout flashing and what HomeCloud reports priced it at on our flashing repair cost page.

Valley flashing

A valley collects water from two roof slopes. In an open metal valley, a visible channel carries that water down the roof, with the roofing cut back on each side.

Closed valleys have roofing over the valley and may use a different underlying protection detail. An absence of visible metal is not, by itself, proof of a missing component. The appropriate method depends on the roofing manufacturer and system. IKO, for example, recommends open metal valleys for its shingles. [3]

Ask which valley detail the proposal includes. If two contractors propose different methods, compare the manufacturer requirements and the work involved rather than choosing solely by appearance.

Drip edge

Drip edge is the metal along a roof’s perimeter. At the eaves, it helps carry water toward the gutter and away from the fascia, the board behind the gutter. Along rake edges, it helps protect the edge of the roof assembly. Its relationship to the underlayment, roofing and gutter matters. [7]

A roof can have new shingles and still have poorly coordinated edge details. Ask whether new drip edge is included and whether the gutter position allows water to drain where intended.

Pipe boots and skylight flashing

A plumbing vent pipe needs a fitted flashing assembly. Many boots use a flexible collar around the pipe and a base integrated with the roof. The collar must fit the pipe, and the assembly must suit the roof material. Oatey cautions against using an oversized collar and filling the gap with sealant. [4]

Boot materials and seals do not necessarily last as long as the surrounding roof. Ask what will be installed during replacement rather than assuming existing boots will remain suitable. Outside a full replacement, see plumbing vent boot and pipe repair.

Skylights usually need flashing matched to the unit, mounting style, roof material and slope. Manufacturer-designed systems coordinate the upper, side and lower drainage details. VELUX, for example, describes kits designed to shed water without depending on exposed sealants for the primary protection. [5]

If the roof is being replaced around an older skylight, price the options while access is available. The decision to retain or replace the unit should consider its condition and the compatible flashing system.

What a chimney cricket does

A cricket is a small raised roof shape on the uphill side of a chimney. It divides the water flow and sends it around the obstruction. The cricket itself needs correctly integrated roofing and flashing. [6]

It is related to flashing but is not simply a strip of metal. Ask whether the chimney needs a cricket, whether an existing one is serviceable and what the proposed work includes.

Does flashing always need to be replaced with the roof?

The answer depends on its condition, compatibility and the manufacturer’s requirements. Existing flashing can have holes, corrosion, incorrect overlaps or dimensions that no longer suit the replacement roof. Some sound, well-integrated components may be retained when the system permits it. Oatey’s guidance, for example, calls for replacement of its standard pipe flashings when the roof is replaced. [4]

The proposal should make that decision explicit. If flashing behind siding will be reused, ask how its condition and integration will be evaluated. If replacement requires siding, trim or masonry work, that work needs an allowance or a defined price.

What to ask before signing a roof proposal

Which flashing and pipe boots are being replaced?
What existing flashing will remain, and why is it suitable?
Does the price include access behind siding and repairs to disturbed finishes?
How will the valleys, chimney and skylights be handled?
Are the flashing materials compatible with the selected roofing and adjacent metals?
How will concealed damage discovered during removal be documented and priced?

Request photographs of details that will become concealed. They provide a useful record of the work without requiring you to climb onto the roof.

Flashing is part of the roof’s water-management system, so its scope belongs in the replacement budget. Pair this guide with our comparison of roof materials and expected lifespan when reviewing proposals.

HomeCloud can help you understand the roof’s observed condition and the proposed repair or replacement work, including the details that are easy to miss in a one-line estimate.