Step Flashing Installation — Preventing Sidewall Roof Leaks

What Step Flashing Is and How It Protects Your Roof

Step flashing is a series of individual L-shaped metal pieces installed at every point where a sloped roof meets a vertical wall surface. Each piece is bent at a 90-degree angle, creating two flanges: one that lies flat on the roof deck beneath a shingle, and one that extends up the sidewall behind the wall covering. The pieces are called "step" flashing because they are installed in a stair-step pattern, one per shingle course, ascending the roof slope alongside the wall.

The principle behind step flashing is straightforward but critical. Water flowing down a roof surface will naturally gravitate toward any vertical obstruction, and the junction between a roof and a wall is one of the most vulnerable areas on any structure. Without flashing at this junction, water wicks behind the shingles through capillary action, saturates the roof deck, and migrates into the wall framing, insulation, and interior finishes. The damage accumulates invisibly for months or years before it becomes apparent as stained drywall, peeling paint, or soft spots in the ceiling.

Step flashing solves this by creating a series of overlapping barriers. Each piece directs water that reaches the wall junction onto the surface of the shingle immediately below it. Because the pieces overlap one another by at least two inches, water cannot travel upward or sideways along the wall. It is forced outward, onto the exposed shingle face, and down the roof to the gutter. The system is simple in concept but demands precise execution. Every piece must be positioned at the correct height relative to the shingle exposure, bent to the correct angle, and secured with the right fasteners in the right locations.

Where Step Flashing Is Required

Any roof-to-wall transition on a sloped roof requires step flashing. The most common locations on Atlanta-area homes include:

• Dormer sidewalls where the main roof slope meets the vertical sides of a dormer window projection
• Two-story wall junctions where a lower roof section terminates against the exterior wall of the second story
• Garage-to-house transitions where a lower garage roof meets the house wall
• Addition tie-ins where a room addition roof connects to the original structure
• Chimney sides where the chimney masonry intersects the roof slope (though chimney flashing involves additional components like cricket flashing and counter-flashing cut into mortar joints)

On complex roof designs common in neighborhoods like Buckhead, Johns Creek, and Alpharetta, a single home may have eight or more locations requiring step flashing. Each one must be executed correctly. A failure at any single junction can produce a leak that damages the structure for years before the source is identified.

Why Each Shingle Course Needs Its Own Step Flashing Piece

One of the most common and damaging shortcuts in residential roofing is the use of a single continuous piece of bent metal along a sidewall instead of individual step flashing pieces at each shingle course. This approach is faster for the installation crew, uses less material, and looks acceptable from the ground. It also fails within a few years.

A continuous piece of L-shaped metal creates an uninterrupted channel between the wall surface and the shingle edges. Wind-driven rain enters the top of this channel and flows downhill behind the shingles, picking up speed and volume as it descends. Capillary action pulls additional water into the gap between the metal and the wall sheathing. The water has nowhere to exit except at the bottom of the channel or at any imperfection in the caulk seal — and caulk is never a permanent solution. Within two to five years, the caulk fails, and every rainstorm delivers water directly to the roof deck, wall studs, and interior of the home.

Individual step flashing pieces eliminate this failure mode entirely. Because each piece is independent and overlaps the one below it, water that enters the system at any point is immediately redirected outward onto the shingle surface. There is no continuous channel for water to follow. There is no reliance on caulk or sealant to maintain the barrier. The system works through gravity and overlap, which means it continues working for the full service life of the roof.

GAF's published installation instructions are explicit on this point: "Install a piece of step flashing beside each shingle course." CertainTeed have identical requirements. There is no manufacturer of asphalt shingles that approves continuous flashing at sidewalls. Any contractor who installs continuous flashing at a sidewall transition is either unaware of manufacturer requirements or has chosen to ignore them. Either situation should concern any homeowner.

Proper Step Flashing Dimensions and Overlap

Standard step flashing pieces measure 5 inches by 7 inches when flat, bent at the center to create a 3.5-inch roof flange and a 3.5-inch wall flange (some specifications call for 4 by 4 inches, while others use 5 by 7 for additional coverage). Each piece must overlap the one below it by a minimum of 2 inches, with 3 inches preferred in high-wind zones. The bottom edge of each step flashing piece must align with the bottom edge of the shingle it accompanies — this ensures that the overlap geometry functions correctly and water is directed outward at each course.

The material matters as well. Galvanized steel, aluminum, and copper are the three standard choices. For most Atlanta residential applications, 26-gauge galvanized steel or .019-inch aluminum provides the right balance of durability, corrosion resistance, and cost. Copper step flashing is appropriate for high-end installations, particularly on slate or architectural-grade roofs where the aesthetic and longevity of copper justify the cost premium. Regardless of material, the pieces must be rigid enough to maintain their shape under the weight of the shingles and during wind events.

Ice and Water Shield: The Critical Layer Behind Step Flashing

Step flashing alone is not sufficient at roof-to-wall junctions. Before any step flashing pieces are installed, the wall sheathing at the transition must be protected with a self-adhering ice and water shield membrane. This requirement is not optional and not a matter of contractor preference. GAF technical bulletins specify that ice and water shield must extend a minimum of 5 inches up the sidewall at every step flashing location.

The ice and water shield serves as a secondary waterproofing barrier behind the metal step flashing. Even properly installed step flashing can, over time, allow small amounts of moisture to reach the wall surface through condensation, ice damming in winter, or the occasional extreme wind-driven rain event. The rubberized asphalt membrane self-seals around the fastener penetrations and creates an impermeable barrier against the wall sheathing. Without it, any moisture that passes the step flashing has direct access to the oriented strand board (OSB) or plywood wall sheathing, which absorbs water readily and begins deteriorating within weeks of sustained exposure.

The 5-inch measurement is a minimum. In areas with high wind exposure, significant roof-to-wall height differentials, or where ice damming is a concern (less common in Atlanta but relevant in the North Georgia mountains), extending the membrane 8 to 12 inches up the wall provides additional protection. The cost difference is negligible, and the insurance against future water infiltration is substantial.

Why Most Contractors Skip This Step

Applying ice and water shield properly at sidewalls requires removing the bottom courses of siding at the junction. This adds labor time, introduces the risk of breaking siding pieces (especially on older vinyl or aged wood clapboard), and creates additional scope that the contractor must manage. Contractors working under tight bid pricing or crew time pressure frequently skip the ice and water shield entirely, relying on the step flashing alone or substituting a bead of roofing caulk.

The result is predictable. Within five to ten years, moisture penetration at sidewall junctions produces rotted wall sheathing, mold growth inside the wall cavity, and interior water damage. The repair costs for this concealed damage routinely exceed $5,000 to $15,000 per junction — costs that would have been entirely prevented by the 30 to 45 minutes of additional labor required to install ice and water shield correctly during the original roof installation.

1 Source does not skip this step. On every roof we install in the Atlanta metro area — from Lawrenceville to Sandy Springs, from Marietta to Johns Creek — ice and water shield is applied to the full height of the step flashing exposure on every sidewall. Our crews are trained specifically on this requirement, and our project managers verify compliance before any siding is reinstalled.

Siding Must Be Removed for Correct Step Flashing Installation

This is where the difference between a specification-grade installation and a shortcut installation becomes most visible — or rather, most invisible, because the failure is concealed behind the siding where no one sees it until the damage is extensive.

To install step flashing and ice and water shield correctly at a roof-to-wall junction, the siding material covering the bottom portion of the wall at that junction must be removed. There is no alternative method that achieves the same result. The ice and water shield must bond directly to the wall sheathing. The step flashing wall flange must extend behind the wall covering. Counter-flashing or the siding itself must overlap the top of the step flashing to prevent water from entering behind the metal. None of this can happen if the siding remains in place.

What Siding Removal Involves

The scope depends on the siding material. For vinyl siding — the most common exterior cladding on homes in metro Atlanta — the process is relatively straightforward. Vinyl siding is designed to be unlocked and removed from the bottom up. A siding removal tool (sometimes called a zip tool) separates the interlocking joints, and the affected courses are lifted off. After the step flashing and ice and water shield are installed, the siding is reinstalled from the bottom up, re-engaging the interlocking joints. When done carefully, there is no visible evidence that the siding was disturbed.

Wood clapboard and fiber cement siding (such as James Hardie) require more careful handling. These materials are nailed or screwed in place and cannot be simply unlocked. Removal involves pulling fasteners, carefully prying the boards free without cracking them, numbering or marking each piece for position, and reinstalling in reverse order. Older wood siding may be brittle, and some breakage is inevitable. In these cases, matching replacement material is sourced and installed.

Stucco presents a unique challenge. Unlike panel or board siding, stucco cannot be removed and reinstalled. Step flashing integration with stucco exteriors requires cutting a reglet (a narrow groove) in the stucco surface, inserting the step flashing flange into the reglet, and sealing with appropriate sealant. This technique is detailed on our stucco flashing installation page.

The Brick Exception

Brick exteriors do not require siding removal in the same way. Instead of tucking step flashing behind a removable wall covering, the step flashing is overlapped by counter-flashing that is cut into the mortar joints of the brick. This technique — called reglet counter-flashing — involves cutting a groove in the mortar joint with a grinder, inserting the counter-flashing lip into the groove, and sealing with high-quality polyurethane sealant. The counter-flashing overlaps the step flashing by at least 2 inches, preventing water from entering behind the step flashing. Ice and water shield is still applied to the wall sheathing behind the brick veneer where accessible.

How 1 Source Installs Step Flashing to Manufacturer Specifications

Every step flashing installation by 1 Source follows the same documented sequence, regardless of whether the project is a full roof replacement, a localized repair, or a re-flash of a previously failed installation. The process is non-negotiable because the manufacturer warranty depends on it.

1. Siding Removal at Affected Junctions The bottom 12 to 16 inches of siding at each roof-to-wall junction is carefully removed and set aside for reinstallation. Vinyl siding is unlocked with a zip tool. Board siding is unfastened and marked for position. Each piece is inspected for damage and replaced if necessary.
2. Wall Sheathing Inspection and Repair With the siding removed, the wall sheathing is exposed and inspected for rot, mold, or previous water damage from failed flashing. Damaged sheathing is cut out and replaced with matching material before proceeding. This inspection step is one of the primary reasons siding removal is essential — it reveals damage that has been hidden for years.
3. Ice and Water Shield Application GAF StormGuard or equivalent self-adhering membrane is applied to the wall sheathing, extending a minimum of 5 inches above the roof deck surface. The membrane is pressed firmly to ensure complete adhesion and wraps down onto the roof deck at least 4 inches to create a continuous seal at the intersection. All seams are overlapped by 3 inches minimum.
4. Starter Flashing Placement The first step flashing piece is positioned at the bottom of the roof-to-wall junction, aligning with the starter strip or first shingle course. The roof flange is secured with a single nail near the top edge, placed where the next shingle course will cover it. The wall flange is left unfastened — it must float to accommodate thermal movement of the metal.
5. Step Flashing Woven with Each Shingle Course As each subsequent shingle course is installed ascending the roof, a step flashing piece is placed alongside the wall. The bottom edge of each step flashing piece aligns with the bottom (exposed) edge of the shingle. Each piece overlaps the one below by a minimum of 2 inches. A single nail secures the roof flange, positioned so the next shingle covers it completely. This process continues to the ridge or to the point where the roof slope terminates at the wall.
6. Counter-Flashing or Siding Reinstallation After all step flashing pieces are installed, the wall covering is reinstalled over the step flashing wall flanges. On vinyl or board siding, the siding overlaps the top of the step flashing by at least 2 inches, creating a weatherproof seal without reliance on caulk. On brick, counter-flashing is cut into the mortar joints. The siding is inspected for tight fit and proper alignment.
7. Final Inspection and Documentation The project manager walks every step flashing junction to verify piece count, overlap dimensions, ice and water shield coverage, and siding fit. Photographs are taken for the project file and for any insurance documentation. Deficiencies are corrected before the crew leaves the site.

This process adds time to every roof installation. The siding removal and reinstallation alone can add two to four hours per junction, depending on the siding type and wall height. But the alternative — a failed flashing system that produces hidden water damage for years — is not something 1 Source is willing to deliver. Our warranty and our reputation depend on getting these details right.

Counter-Flashing: The Protective Layer Over Step Flashing

Step flashing on its own handles the roof-side of the water management equation. Counter-flashing handles the wall side. Counter-flashing is a second layer of metal (or the siding material itself, depending on the wall type) that overlaps the top edge of the step flashing wall flange, preventing water from entering behind the flashing from above.

On homes with vinyl, wood, or fiber cement siding, the siding itself acts as the counter-flashing. When the siding is reinstalled over the step flashing wall flanges, the bottom edge of each siding course covers the top of the step flashing. Water running down the wall surface hits the siding, flows outward on the siding face, and drips off the siding bottom edge onto the step flashing surface below, which directs it onto the shingle. The system works as designed because the siding overlaps the flashing, not the other way around.

On brick or stone exteriors, a separate counter-flashing piece is fabricated and installed. This piece is L-shaped, with the upper flange inserted into a saw-cut groove (reglet) in the mortar joint and the lower flange extending down over the step flashing. The reglet is sealed with polyurethane sealant to prevent water from entering the groove. The counter-flashing overlaps the step flashing by at least 2 inches, creating a two-layer barrier at every course.

Counter-flashing is also critical at chimney-to-roof transitions, where it overlaps the base flashing and step flashing on the sides and back of the chimney. Our sidewall flashing page covers additional counter-flashing scenarios for complex wall-to-roof intersections.

Why Caulk Is Not Counter-Flashing

A disturbingly common practice among contractors is to skip counter-flashing entirely and instead run a bead of roofing caulk along the top edge of the step flashing where it meets the wall. This approach is not approved by any manufacturer, does not meet building code, and has a predictable lifespan of two to five years before the caulk cracks, shrinks, or separates from the surface.

Roofing caulk is a maintenance material, not a structural waterproofing component. It is appropriate for sealing small penetrations, patching minor gaps, or as a supplementary seal behind properly installed metal flashing. It is never appropriate as the primary barrier against water infiltration at a sidewall junction. When you see caulk as the only thing keeping water from entering behind step flashing, you are looking at a temporary repair that was installed as if it were permanent.

Common Step Flashing Mistakes That Cause Sidewall Leaks

After inspecting thousands of roofs across the Atlanta metro area, the 1 Source team has documented a consistent set of installation failures that produce sidewall leaks. These mistakes appear on roofs of all ages and price points, from 30-year-old ranch homes in Lawrenceville to 5-year-old custom builds in Sandy Springs. The common thread is that these shortcuts save the installing contractor 30 to 60 minutes of labor per junction while creating leak conditions that cost the homeowner thousands of dollars in concealed damage.

Continuous Flashing Instead of Stepped Pieces

The single most common failure. One continuous piece of bent metal is run along the entire sidewall junction instead of individual pieces woven at each course. As described earlier, this creates a channel that funnels water behind the shingles. We find this on roughly 40 percent of the sidewall junctions we inspect.

Siding Left in Place Over Step Flashing

The second most common failure. Step flashing pieces are installed, but the siding was never removed. The step flashing wall flange simply butts against the bottom edge of the siding, with caulk filling the gap. The ice and water shield was never applied because the wall sheathing was never exposed. Water enters behind the siding above the flashing and migrates down the wall behind the step flashing, bypassing the system entirely.

No Ice and Water Shield Behind the Step Flashing

Even when siding is removed and step flashing is properly woven at each course, some contractors omit the ice and water shield membrane on the wall sheathing. The step flashing handles normal water flow, but any water that reaches the wall surface — through wind-driven rain, ice damming, or condensation — has direct access to the OSB or plywood sheathing. Over time, this produces rot and mold in the wall cavity.

Incorrect Overlap Between Step Flashing Pieces

Pieces that overlap by less than 2 inches allow water to travel upward between them through capillary action, particularly during wind-driven rain events. This is most common when installers attempt to stretch a limited supply of step flashing pieces across a long sidewall run by increasing the spacing between pieces.

Nailing Through the Step Flashing Wall Flange

Each step flashing piece should be secured with one nail through the roof flange only, positioned where the next shingle covers it. Nailing through the wall flange creates a penetration point for water and prevents the metal from expanding and contracting with temperature changes, which can cause the piece to buckle or lift over time.

Caulk as the Primary Seal

Any installation that relies on caulk to maintain the waterproof barrier at a sidewall junction is a temporary installation. Caulk degrades under UV exposure, thermal cycling, and moisture. Within three to five years in Atlanta's climate — with its summer heat, winter freezes, and heavy spring rains — caulk at a sidewall junction will crack and fail. When it does, every rainstorm delivers water into the wall cavity.

GAF Technical Bulletins on Step Flashing

GAF, the largest roofing manufacturer in North America, publishes detailed technical bulletins and installation guides that address step flashing requirements for warranty compliance. As a GAF Certified contractor, 1 Source has access to the full library of these technical resources and trains our installation crews directly from these documents.

Key requirements from GAF's published guidelines include:

• Individual step flashing at every course. A separate piece of step flashing must accompany each shingle at every roof-to-wall junction. Continuous flashing is prohibited.
• Minimum 5-inch ice and water shield extension up the sidewall. The self-adhering membrane must be applied to the bare wall sheathing before step flashing is installed. This is required at all sidewall junctions, regardless of climate zone.
• Step flashing dimensions: GAF specifies a minimum 4-by-4-inch step flashing piece (when measured as a flat L-shape), though 5-by-7-inch pieces are recommended for enhanced coverage.
• Minimum 2-inch overlap between consecutive step flashing pieces. The overlap must be measured from the exposed bottom edge of the upper piece to the exposed bottom edge of the lower piece.
• Single fastener per piece, driven through the roof flange only, positioned in the upper corner where it will be covered by the next shingle course and the next step flashing piece.
• Counter-flashing or wall covering must overlap the top edge of the step flashing wall flange by a minimum of 2 inches.

These requirements are not suggestions. They are conditions of GAF's warranty coverage. A roof installed without proper step flashing at sidewall junctions does not qualify for GAF's Golden Pledge or System Plus warranties, even if every other aspect of the installation is flawless. For homeowners who have invested in a GAF warranty through a certified contractor, this distinction matters — a single improperly flashed sidewall can void the coverage for the entire roof system.

For a comprehensive overview of all manufacturer installation requirements, visit our roofing technical standards page and our flashing standards reference.

Insurance Coverage for Step Flashing and Siding Work

Homeowners filing insurance claims for roof replacement after storm damage often do not realize that step flashing installation and the associated siding work are legitimate line items on the claim. Insurance adjusters working from Xactimate pricing software include step flashing as part of the standard roof replacement scope — it is a code-required component, and no insurance company disputes the necessity of proper flashing at roof-to-wall junctions.

The siding component is where many homeowners leave money on the table. When siding must be removed to install step flashing and ice and water shield, the cost of siding removal, handling, and reinstallation is a billable line item on the insurance claim. If any siding pieces are damaged during removal and cannot be reused, replacement siding is also covered. And here is where the scope can expand significantly: if enough siding is disturbed across multiple junctions — and the replacement pieces do not match the existing siding in color or weathering — the insurance carrier may approve full siding replacement or full exterior repainting to maintain a uniform appearance.

This is not an unusual outcome. On homes with older vinyl siding that has faded or been discontinued, matching new pieces to the existing siding is often impossible. Insurance carriers recognize this and will approve the additional scope to ensure the home is restored to its pre-loss condition. 1 Source documents every piece of siding we remove, photographs any color discrepancies or damage, and submits this documentation to the insurance adjuster as part of the supplement process.

How 1 Source Follows Manufacturer Specs on Every Step Flashing Installation

The difference between a roof that lasts 30 years without a sidewall leak and one that develops concealed water damage within 5 years comes down to flashing execution. It is not about the shingle brand, the underlayment weight, or the number of certifications displayed on a truck. It is about whether each step flashing piece was installed at each course, whether the ice and water shield went up the wall, and whether the siding was removed and reinstalled to allow it.

1 Source addresses this through three mechanisms that most roofing contractors do not employ:

• Crew training on manufacturer installation manuals. Every crew member working a 1 Source job site has been trained on GAF, CertainTeed step flashing specifications. Training is refreshed annually and when manufacturer guidelines are updated.
• Project manager verification at every junction. Before siding is reinstalled at any step flashing location, a 1 Source project manager inspects the ice and water shield application, step flashing placement, overlap dimensions, and fastener locations. This inspection is documented with photographs.
• Photographic documentation for warranty files. Every step flashing installation is photographed before the wall covering is reinstalled. These photos become part of the project record and are available to the homeowner, the insurance company, and the manufacturer in the event of a warranty claim. If a question about flashing installation arises 10 years after the roof was completed, the photographs provide definitive evidence of what was installed and how.

This level of documentation and verification is rare in residential roofing. It takes additional time on every project. It costs us more per installation than it would cost to skip these steps. And it is the reason our sidewall leak callback rate is effectively zero. We would rather spend 45 extra minutes per junction during installation than spend 3 days per junction on a remediation project that should never have been necessary.

For a full overview of our approach to roofing, including our complete roof replacement process, visit our services pages or call (404) 277-1377 to speak with a project manager directly.

Learn More About Roof Flashing and Installation Standards