Roofing Flashing Standards — GAF and CertainTeed Manufacturer Specifications
The definitive guide to step flashing, wall flashing, chimney flashing, metal re-use, and the new 5-inch sidewall requirement.
Certified by Industry-Leading Manufacturers
Manufacturer Technical Bulletins
- Re-Use of Metal Flashings (GAF)
- Re-Use of Existing Flashing (CertainTeed)
Why Roof Flashing Is the Most Critical Component of Your Roof System
Flashing accounts for less than five percent of a roof's total material cost. It also accounts for the majority of residential roof leaks in metro Atlanta. That imbalance tells you everything you need to know about its importance relative to shingles, underlayment, and ventilation components. Flashing is the metal barrier installed at every point where the roof plane intersects a vertical surface, a penetration, or another roof plane. Chimneys, sidewalls, headwalls, skylights, vent pipes, dormers — every one of these transitions requires flashing that is correctly sized, correctly profiled, and correctly integrated with the surrounding shingle courses and underlayment.
The physics are straightforward. Water follows gravity downhill across a roof surface until it encounters an obstruction. At that obstruction — a chimney, a wall, a pipe — the water must be redirected onto the shingle surface below without penetrating beneath the roofing material. That is what flashing does. When it is installed correctly, water never contacts the roof deck at a transition point. When it is installed incorrectly — using wrong dimensions, wrong overlap, wrong sealant, or no counter-flashing — water enters the roof system at precisely the points where the structure is most vulnerable.
GAF and CertainTeed both publish detailed flashing specifications that certified contractors are required to follow. These are not optional guidelines. They are installation requirements that determine whether a manufacturer warranty is valid or void. A contractor who installs GAF shingles but deviates from GAF's flashing details has installed a roof that will not be covered under the manufacturer's warranty program — regardless of how the shingle field itself was installed. The flashing system and the shingle system are inseparable components of a warranted installation.
1 Source Roofing follows manufacturer flashing specifications on every project because our certifications with GAF, CertainTeed require it — and because we have seen, on hundreds of re-roofing projects, exactly what happens when previous contractors cut corners at transition points. For a detailed look at our flashing installation services, see our roof flashing installation page.
Step Flashing — Installation Standards from GAF and CertainTeed
Step flashing is used wherever a roof slope runs alongside a vertical wall — the sidewall condition that appears on virtually every residential roof in metro Atlanta where dormers, second-story additions, or attached garages create roof-to-wall junctions. The step flashing method uses individual L-shaped metal pieces, one installed with each course of shingles, creating a stair-step pattern that channels water onto the shingle surface below. Each piece overlaps the one beneath it, ensuring continuous water shedding even under heavy rain loads.
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GAF Step Flashing Specifications
GAF's published step flashing detail requires each step flashing piece to extend a minimum of 4 inches up the wall surface and 4 inches onto the roof deck beneath the shingle. The minimum overlap between consecutive step flashing pieces is 2 inches. GAF specifies 26-gauge galvanized steel or equivalent corrosion-resistant metal. Each step flashing piece must be fastened to the roof deck — not the wall — using a single nail placed at the top corner of the deck leg. Fastening to the wall creates a rigid connection that does not accommodate differential movement between the roof and wall structures, leading to fatigue cracking over thermal cycles.
The critical addition to GAF's step flashing detail is the ice and water shield requirement at sidewalls. GAF now requires a minimum of 5 inches of self-adhered leak barrier extending up the sidewall beneath the step flashing. This is a departure from the previous 4-inch standard and from the practices that many experienced contractors learned years ago. The additional inch addresses capillary draw — the phenomenon where water wicks upward between closely spaced surfaces through surface tension. At a roof-to-wall junction, wind-driven rain can force water into the gap between step flashing and the wall surface, where capillary action pulls it higher than the flashing coverage. The 5-inch minimum provides the safety margin that the 4-inch application did not.
CertainTeed Step Flashing Specifications
CertainTeed's step flashing requirements align closely with GAF's fundamentals but differ in several details. CertainTeed specifies step flashing pieces a minimum of 10 inches long and 2 inches wider than the face of the shingles being installed. For standard architectural shingles with a 5-5/8-inch exposure, this translates to a minimum step flashing width of approximately 7-5/8 inches. The wall leg must extend a minimum of 5 inches up the wall surface. CertainTeed requires a minimum 2-inch overlap between consecutive pieces, matching GAF's specification.
CertainTeed also specifies that step flashing must be installed with a full-width strip of self-adhered underlayment (ice and water shield) at all sidewall junctions, extending from the edge of the roof plane a minimum of 12 inches onto the roof deck surface. This underlayment acts as a secondary water barrier beneath the step flashing and shingles, providing protection against water infiltration if the primary flashing system is compromised by wind-driven rain, ice damming, or debris accumulation in the flashing channel.
Both manufacturers are explicit: caulk, roof cement, or sealant alone is never an acceptable substitute for properly installed step flashing. We see this shortcut regularly on re-roofing projects throughout Lawrenceville, Alpharetta, and Sandy Springs — a thick bead of sealant where metal step flashing should be. Sealant degrades within three to five years under Georgia's UV exposure and thermal cycling. Metal flashing, properly installed, lasts the life of the roof.
Headwall and Continuous Wall Flashing Standards
Headwall flashing — also called apron flashing or continuous wall flashing — is used where the bottom edge of a wall sits on top of a roof slope. This condition is common on two-story homes where the second floor wall extends down to meet a lower roof plane, on dormer faces, and at the base of clerestory walls. Unlike step flashing, which uses individual pieces at each shingle course, headwall flashing is a single continuous piece of metal bent into an L-profile that covers the full width of the wall-to-roof junction.
GAF Headwall Flashing Detail
GAF specifies headwall flashing with a minimum 4-inch wall leg and a minimum 4-inch roof leg. The roof leg extends beneath the shingles above the junction, while the wall leg extends up behind the wall cladding or beneath the counter-flashing. GAF requires self-adhered leak barrier (ice and water shield) extending from the headwall a minimum of 24 inches down the roof slope, providing secondary protection beneath the continuous flashing piece. The shingles immediately below the headwall must terminate no closer than 2 inches from the base of the wall, allowing water to flow freely from the flashing onto the shingle surface without being trapped against the wall.
CertainTeed Headwall Flashing Detail
CertainTeed's headwall specification requires the flashing to extend a minimum of 5 inches up the wall and 4 inches onto the roof deck. The wall leg must be covered by counter-flashing, wall cladding, or a reglet cut into masonry — exposed flashing ends are not acceptable for warranty-eligible installations. CertainTeed requires a full-width application of self-adhered underlayment at the headwall extending a minimum of 18 inches onto the roof deck surface from the base of the wall.
One detail that distinguishes competent flashing installation from negligent installation at headwalls: the end dams. At each end of a continuous headwall flashing piece, the metal must be bent upward to create a small dam that prevents water from running off the end of the flashing and behind the adjacent shingle courses. This is a detail specified by both manufacturers, routinely omitted by uncertified contractors, and visible only during installation or upon removing the shingles for re-roofing. 1 Source installs end dams on every headwall flashing piece because the manufacturers require it and because leaving water a pathway behind flashing defeats the purpose of installing the flashing in the first place.
Chimney Flashing — The Most Complex Flashing Application on Any Roof
Chimney flashing is the most labor-intensive and technically demanding flashing application on a residential roof. A chimney creates four distinct conditions on a single penetration: a headwall at the front (downslope) face, step flashing along both sides, and a back pan or cricket at the rear (upslope) face. Each condition requires its own flashing detail, and the four details must integrate seamlessly to prevent water entry from any direction. A chimney leaking from a failed flashing system is the single most common roof leak complaint we encounter on homes in Gwinnett, Fulton, and Cobb counties.
Front (Apron) Flashing
The front face of the chimney receives a continuous apron flashing that extends beneath the counter-flashing embedded in the mortar joint above. Both GAF and CertainTeed require the apron to extend a minimum of 4 inches up the chimney face and a minimum of 4 inches onto the roof deck beneath the shingles. Ice and water shield must extend from the chimney base a minimum of 24 inches down the roof slope, and it should also extend up the chimney face beneath the apron flashing by at least 4 inches. This creates a two-layer defense — the ice and water shield provides waterproof adhesion to both surfaces, while the metal apron provides the durable, long-term physical barrier.
Side Step Flashing
Both sides of the chimney receive step flashing installed using the same specifications as sidewall step flashing — individual L-shaped pieces at each shingle course, with a minimum 2-inch overlap between pieces. The wall leg extends up the chimney face and is covered by counter-flashing. Ice and water shield must extend up the chimney sides and onto the roof deck a minimum of 12 inches from the chimney face.
Back Pan and Cricket Construction
The back (upslope) face of the chimney is the most vulnerable point in the entire assembly. Water flowing down the roof slope hits the back face of the chimney directly, and without a properly constructed diverter, it pools against the masonry. Both GAF and CertainTeed require a cricket (also called a saddle) behind any chimney wider than 30 inches. A cricket is a peaked metal structure that divides the water flow and redirects it around both sides of the chimney. Chimneys narrower than 30 inches receive a back pan — a continuous piece of metal bent to direct water around the chimney sides without the peaked construction of a full cricket.
Cricket construction requires sheet metal fabrication skills that not every roofing crew possesses. The cricket must be soldered or mechanically seamed at its peak, covered with ice and water shield on the roof deck side, and integrated with the step flashing on both sides of the chimney. A poorly constructed cricket that allows water to pool behind the chimney will fail — sometimes within a single storm season.
Counter-Flashing
Counter-flashing is the exterior-visible metal that overlaps the top edge of the step flashing and apron flashing on all four sides of the chimney. Both manufacturers require counter-flashing to be embedded into the mortar joints of the chimney masonry, not surface-mounted with sealant. The mortar joint is cut (using a grinder or hand tool) to a depth of approximately 1 to 1.5 inches, the counter-flashing lead is inserted, and the joint is sealed with high-quality polyurethane sealant. Surface-mounted counter-flashing — held in place with caulk alone — will separate from the chimney face within a few years as the sealant degrades, exposing the step flashing edges to direct water entry.
| Chimney Flashing Component | GAF Specification | CertainTeed Specification |
|---|---|---|
| Apron (front face) | 4" up chimney, 4" on deck | 5" up chimney, 4" on deck |
| Step flashing (sides) | 4" wall leg, 4" deck leg, 2" overlap | 5" wall leg, 2" overlap minimum |
| Cricket required | Chimney width > 30" | Chimney width > 30" |
| Counter-flashing | Embedded in mortar, 1" depth | Embedded in mortar, 1-1.5" depth |
| Ice & water shield | 24" from chimney base, all sides | 12" minimum from chimney, all sides |
| Metal gauge | 26-gauge minimum | 26-gauge minimum |
Concerned About Your Roof's Flashing?
Flashing failure is the leading cause of residential roof leaks. 1 Source Roofing inspects every flashing detail during our free roof assessments. Call today to schedule yours.
Schedule Your Free InspectionRe-Use of Metal Flashings During Re-Roofing — What the Manufacturers Actually Say
One of the most contentious decisions during a roof replacement is whether to re-use existing metal flashings or replace them with new material. This is a cost-driven decision for many contractors — new flashing fabrication and installation adds labor hours and material cost to a project. But both GAF and CertainTeed have published explicit guidelines on when existing metal flashings can and cannot be re-used, and certified contractors are bound by those guidelines.
GAF Re-Use of Metal Flashings Bulletin
GAF's position is documented in their Re-Use of Metal Flashings technical bulletin. The core requirement is a visual and functional inspection of each existing flashing component. Metal flashings may be considered for re-use only when all of the following conditions are met:
- The metal is free of rust, corrosion, and pitting on both the exposed and concealed surfaces
- The metal maintains its original profile — no bends, kinks, dents, or distortions from prior removal or manipulation
- All sealant connections are intact and have not hardened, cracked, or separated
- The metal gauge is adequate for the installation — thin or lightweight flashings that have lost rigidity through fatigue cannot be re-used
- The flashing dimensions meet current specification requirements — older flashings that were fabricated to outdated dimensions may not meet current standards even if the metal itself is in acceptable condition
Any flashing that fails any single criterion must be replaced. GAF does not permit partial assessments — a flashing piece that passes four criteria but fails one is a replacement, not a re-use candidate.
CertainTeed Re-Use Flashing Bulletin
CertainTeed's guidance on flashing re-use follows a similar framework. Their technical bulletin emphasizes that re-used flashings must be compatible with the new roofing system being installed. This compatibility requirement extends beyond physical condition to include material compatibility — for example, copper flashing that was previously used with copper-compatible sealants must not be re-used with sealants that react with copper. Galvanized steel flashings that show any surface oxidation beyond superficial patina are not re-use candidates under CertainTeed's guidelines.
CertainTeed also addresses the practical concern that many contractors overlook: existing flashing that was installed with a different shingle exposure or profile may not align correctly with the new shingle system. A step flashing piece that was sized for a 5-inch shingle exposure will not provide correct coverage when installed with shingles that have a 5-5/8-inch exposure. The dimensional mismatch creates a gap in coverage at every course transition, and that gap is a water entry point.
The 1 Source Standard
Our practice on flashing re-use is straightforward: we inspect every existing flashing component during the initial assessment and document its condition photographically. If it passes the manufacturer's criteria, we discuss the re-use option with the homeowner. If it fails, we replace it. In practice, on homes in the Atlanta metro area that are undergoing their first re-roofing (typically at the 20 to 25 year mark), the majority of existing flashings show sufficient corrosion, profile deformation, or sealant failure to warrant replacement. The cost difference between re-using and replacing flashing on a typical residential project is a fraction of the total project cost — and the risk of re-using compromised flashing far outweighs that savings.
The GAF 5-Inch Sidewall Ice and Water Shield Requirement
This is the specification change that separates contractors who stay current from contractors who are still installing by habits formed a decade ago. GAF's updated installation requirements now mandate a minimum of 5 inches of self-adhered ice and water shield (leak barrier) extending up the sidewall at every roof-to-wall transition. The previous standard was 4 inches. That single inch is the difference between a roof system that can withstand wind-driven rain at sidewall junctions and one that cannot.
The technical basis for the change is capillary action. When water is forced between the step flashing and the wall surface by wind pressure — a routine occurrence during the thunderstorms that sweep through metro Atlanta from April through October — surface tension causes the water to wick upward between the two closely spaced surfaces. Four inches of ice and water shield coverage on the wall surface left insufficient margin for this capillary draw under severe conditions. Water that wicked above the 4-inch line entered the wall cavity and traveled down to the roof deck, bypassing the flashing system entirely.
The 5-inch requirement applies to all new installations and re-roofing projects where GAF products are being installed under a manufacturer warranty. It is not retroactive to existing installations, but any roof being replaced today must comply with current specifications to receive warranty coverage. This means that a contractor who installs GAF shingles with only 4 inches of ice and water shield at the sidewalls — following the outdated standard — has installed a roof that does not meet the current specification and may not be eligible for GAF warranty coverage.
1 Source adopted the 5-inch standard as soon as GAF published the updated specification. Our crews measure and verify sidewall coverage at every roof-to-wall junction during installation. We photograph the ice and water shield application before step flashing is installed, documenting the coverage dimension for the project file. This documentation protects both the homeowner and our company — it provides proof of specification compliance if a warranty claim is ever filed.
For more detail on underlayment and ice and water shield requirements across the full roof system, see our underlayment and ice dam protection page.
Common Flashing Failures We See on Atlanta Roofs
After inspecting thousands of roofs across Gwinnett County, Fulton County, and the broader metro Atlanta area, we have documented the same flashing failures repeating across projects installed by different contractors, on different house styles, in different decades. These are not random defects. They are systemic failures that result from either ignorance of manufacturer specifications or deliberate shortcuts taken to reduce labor time on the project.
- Sealant-only sidewall applications. The most common failure we encounter. Instead of installing metal step flashing at each shingle course, the contractor applied a bead of roof cement or polyurethane sealant along the wall-to-roof junction. This method provides temporary adhesion that degrades within three to five years under UV exposure and thermal cycling. Once the sealant cracks or separates, water enters directly at the junction with no secondary barrier.
- Continuous flashing used where step flashing is required. Some contractors install a single continuous L-shaped piece of metal along the entire length of a sidewall, rather than individual step flashing pieces at each shingle course. This creates a damming condition — water that enters beneath the continuous piece has no outlet and pools on the roof deck beneath the flashing. Step flashing prevents this because each piece overlaps the one below it, creating a cascading drainage path.
- Inadequate chimney flashing with no counter-flashing. We regularly see chimney flashing that consists of step flashing only — no counter-flashing embedded in the mortar joints. The exposed top edges of the step flashing allow water to enter behind the metal during any significant rain event. Counter-flashing is not optional. Both GAF and CertainTeed require it.
- Missing cricket on wide chimneys. Chimneys wider than 30 inches without a properly constructed cricket behind them accumulate water, debris, and ice against the back face of the masonry. This pooling creates hydrostatic pressure that forces water beneath the flashing and into the roof deck. A cricket eliminates pooling by diverting water around the chimney.
- Kick-out flashing omitted at eave-wall intersections. Where a roof slope terminates at a wall (rather than continuing alongside it), a kick-out flashing piece must be installed to direct water from the step flashing channel into the gutter rather than behind the wall cladding. This detail is frequently omitted, and the result is water damage inside the wall cavity that may not become visible for years.
Every one of these failures is avoidable by following manufacturer installation specifications. 1 Source documents the flashing condition on every inspection — if your current roof has any of these conditions, we will identify them and explain your options. Call (404) 277-1377 to schedule a free assessment.
Frequently Asked Questions About Roof Flashing
Answers to the flashing questions Atlanta homeowners ask most
Can existing metal flashings be re-used during a roof replacement?
Both GAF and CertainTeed publish specific guidelines on metal flashing re-use. The flashing must be free of corrosion, maintain its original profile without bends or distortion, and show no signs of sealant degradation. GAF's Re-Use of Metal Flashings bulletin outlines the inspection protocol — any flashing that fails visual or functional assessment must be replaced with new material. Reusing compromised flashing is one of the most common warranty-voiding shortcuts in the industry. Call 1 Source at (404) 277-1377 for an honest assessment of your existing flashing condition.
What is the GAF 5-inch sidewall ice and water shield requirement?
GAF now requires a minimum 5-inch application of ice and water shield (leak barrier) extending up the sidewall at all roof-to-wall transitions. This is a change from the older 4-inch standard that many contractors still follow. The additional inch of coverage addresses the capillary action that draws water behind step flashing during wind-driven rain events. This requirement applies to all GAF warranty-eligible installations and is verified during manufacturer inspections.
What is the difference between step flashing and continuous wall flashing?
Step flashing consists of individual L-shaped metal pieces installed at each shingle course where the roof meets a vertical wall. Continuous wall flashing is a single piece of metal bent to cover the entire junction between a roof slope and a vertical wall, typically used at headwall conditions where the roof slopes toward the wall. Both GAF and CertainTeed specify step flashing for sidewall applications and continuous flashing for headwall conditions. Using the wrong type in the wrong location is a common installation error.
How should chimney flashing be installed according to manufacturer specifications?
Chimney flashing is a multi-component system requiring base flashing (apron) at the front face, step flashing along both sides, a cricket or saddle behind the chimney for any chimney wider than 30 inches, and counter-flashing embedded into the mortar joints. The counter-flashing overlaps the step flashing to create a two-layer defense. Ice and water shield underlayment must extend a minimum of 24 inches beyond the chimney on all sides. Sealant alone is never an acceptable installation method.
What gauge metal should be used for roof flashing?
Both GAF and CertainTeed specify minimum 26-gauge galvanized steel or equivalent aluminum for step and wall flashing. For chimney flashing, 26-gauge is the minimum but 24-gauge is recommended for long-term durability. Copper is acceptable and preferred for high-end installations, though it requires isolation from galvanized or aluminum components to prevent galvanic corrosion. Lighter gauge material lacks the rigidity to maintain its profile over decades of thermal cycling.
Technical Bulletins from GAF and CertainTeed
The information on this page is backed by official manufacturer technical bulletins. These documents provide the installation specifications, warranty requirements, and best practices that certified contractors like 1 Source Roofing follow on every project.