Where Is Step Flashing Used on a Roof

Step flashing is a critical roofing detail used where a roof surface meets a vertical wall or penetrating feature to prevent water intrusion at intersections. This article explains the exact locations, materials, installation basics, common mistakes, inspection tips, and repair options so homeowners and inspectors can identify when and why step flashing is required.

Location	Why Step Flashing Is Used	Typical Material
Roof-To-Wall Intersections	Diverts water from wall downward onto roof surface	Galvanized Steel, Copper, Aluminum
Chimneys And Sidewalls	Seals vertical masonry or siding against roof	Galvanized Steel, Copper
Dormers	Protects junctions of dormer wall and roof plane	Galvanized Steel, Aluminum
Skylights (perimeters)	Helps shed water away from skylight curb	Aluminum, Galvanized Steel

What Is Step Flashing And How It Works

Step flashing consists of individual L-shaped pieces of metal installed sequentially where a sloped roof meets a vertical surface. Each piece overlaps the next and is integrated with the roof shingles and wall weather barrier to create a continuous water-shedding system. Properly installed step flashing channels water over shingles and away from the wall, preventing leaks at this vulnerable junction.

Primary Locations Where Step Flashing Is Used

Step flashing is used wherever a sloped roof abuts a vertical surface or penetrating element. The most common locations include roof-to-wall intersections, chimneys and sidewalls, dormers, and skylight perimeters. These are the typical places inspectors and roofers check first for step flashing presence and condition.

Roof-To-Wall Intersections

Where the roof plane meets an exterior wall, step flashing is essential to prevent water from running behind siding or into wall assemblies. Each flashing piece is tucked behind the wall cladding and nailed to the roof deck under each shingle course. This prevents capillary action and forces water outward over the shingle laps.

Chimneys And Masonry Sidewalls

Chimneys and masonry walls require both step flashing at the sides and a continuous counterflashing set into the masonry above. Step flashing lines the transition between chimney bases or sidewalls and the roof covering, channeling water into the roof’s drainage path. Without step flashing, water can seep into masonry joints and lead to interior leaks or structural damage.

Dormers And Small Vertical Projections

Dormers present multiple roof-to-wall junctions where step flashing is used along each side and at the base where the dormer meets the main roof. Flashing must be carefully integrated with dormer siding and roof shingles. Correct step flashing around dormers preserves both the roof and the dormer wall from chronic leakage.

Skylights And Curbs

Skylights with curbs or raised frames require step flashing on the sides where the curb meets the surrounding shingles. Typically a continuous flashing headwall or metal curb flashing is used along with step flashing to guide water away from the skylight frame. Step flashing minimizes the risk of water pooling and penetrating around skylight perimeters.

Materials Used For Step Flashing

Step flashing is manufactured from durable, corrosion-resistant metals sized to match common shingle exposures, typically 3″ x 3″ or 4″ x 4″ legs. Common materials include galvanized steel, aluminum, and copper. Material selection depends on budget, local climate, and compatibility with adjacent materials like brick and copper roofing.

Basic Installation Principles

Proper step flashing requires alternating placement with the roofing shingles so that one leg slides behind the wall cladding and the other leg lies over the shingle. Flashing pieces should overlap by at least 2 inches and be securely fastened without overdriving nails. Correct sequencing with shingles and the wall weather barrier is essential to create a continuous, layered drainage plane.

Key Installation Steps

• Install a water-resistive barrier on the wall and shingle starter course on the roof.
• Tuck the inner leg of each flashing piece behind the siding or WRB and lay the outer leg over the shingle course.
• Overlap each step flashing piece at least 2 inches and fasten to the roof deck above the shingle line.
• Install counterflashing or seal the upper wall termination as required for masonry or siding.

Following manufacturer and local building code guidelines during installation reduces the risk of leaks and costly callbacks.

Common Mistakes And How They Lead To Leaks

Improperly installed step flashing is a frequent cause of roof leaks. Common errors include using continuous flashing in place of stepped pieces, failing to tuck flashing behind the siding, inadequate overlaps, and nailing through the inner leg into the wall. These mistakes allow water to bypass the flashing and enter the wall or attic spaces.

Specific Faults To Watch For

• Missing step flashing at roof-to-wall junctions.
• Flashing painted, corroded, or mismatched to adjacent roofing metals.
• Flashing installed over the siding instead of behind it.
• Insufficient overlap or improperly seated counterflashing where required.

Inspection And Maintenance Tips

Regular inspections reduce the chance of undetected leaks. Homeowners and inspectors should look for missing or corroded flashing, seals that have deteriorated, and shingles that lift or gap around flashing locations. Annual roof inspections and after-storm checks are recommended to catch problems early.

What To Inspect

• Visible flashing condition for rust or deformation.
• Seams and overlaps for gaps or improper nailing.
• Wall cladding junctions to ensure flashing is tucked behind the siding or WRB.
• Signs of staining or moisture in attics adjacent to flashing locations.

Repair Options And Temporary Measures

Small issues like a single loose flashing can sometimes be repaired by reseating and securing the piece and applying a compatible sealant. Larger problems—such as missing flashing or widespread corrosion—usually require professional replacement of step flashing and possibly counterflashing. Temporary sealants can slow a leak but are not a substitute for proper flashing replacement.

When A Temporary Fix Is Acceptable

Temporary fixes such as roof cement or flashing tape may be used to control leaks until professional repairs are made, especially during storms or when immediate access is limited. A scheduled permanent repair should follow to meet long-term performance expectations.

Costs And When To Call A Professional

Repairing or replacing step flashing can range from modest to significant depending on roof complexity, material selected, and whether shingles or siding must be removed. Simple localized repairs are lower cost; full re-flashing at multiple roof-to-wall intersections increases labor and material expenses. Engage a licensed roofing contractor when flashing replacement involves structural penetrations, masonry counterflashing, or extensive roof work.

Factors That Influence Cost

• Type of metal used (galvanized steel vs. copper).
• Accessibility and roof pitch.
• Extent of shingle or siding removal required.
• Need for counterflashing in masonry walls.

Code, Best Practices, And Compatibility Considerations

Building codes and manufacturer instructions often specify flashing details, overlap dimensions, and material compatibility. Using dissimilar metals (for example, copper flashing with aluminum roofing) can accelerate corrosion. Following local code requirements and manufacturer guidance ensures a durable and compliant installation.

Material Compatibility

Galvanic corrosion can occur when incompatible metals contact and are exposed to moisture. Roofers should isolate dissimilar metals with non-conductive barriers or choose materials that are inherently compatible. This practice extends the service life of flashing and adjacent roof components.

Summary Of Best Practices

Step flashing is required at most roof-to-vertical junctions and must be integrated with shingles and wall weather barriers for effective performance. Regular inspection, prompt repair of damaged flashing, and use of compatible materials are essential. Proper installation and maintenance of step flashing significantly reduce the risk of roof leaks and water damage.