By The Roofing Brief Team. Last reviewed: October 2026.
Step flashing is bent sheet metal installed one piece per shingle course where a sloped roof meets a vertical wall, chimney, or dormer side. Each piece is L-shaped, with at least a 4-inch leg up the wall and a 4-inch leg onto the roof under IRC R905.2.8.3, woven into the shingle course immediately above it so water sheds onto the shingle and not behind the wall cladding. On asphalt shingle roofs, the step-flashing requirement comes from the shingle manufacturers: GAF’s Timberline HDZ installation instructions show 5 inch by 5 inch legs, 2 inch overlaps and 2 nails per piece, and Owens Corning’s Roofer’s Guide uses the same 10 inch piece, 2 inches wider than the exposure, bent 5 and 5. The model code is looser: R905.2.8.3 in the 2021 and 2024 editions says base flashing against a vertical sidewall “shall be continuous or step flashing”, but R905.2.8 also requires flashing to follow the shingle manufacturer’s approved installation instructions, so an inspector can hold you to the maker’s step-flashing detail. For a wider overview, see our flashing on a house overview.
The short version
- Code minimum: legs of 4 in by 4 in (IRC R905.2.8.3), metal at least 0.019 in thick, No. 26 galvanized (R903.2.1, R905.2.8.1).
- ARMA sizing rule: at least 10 in long, bent 5 in onto the roof and 5 in up the wall, and at least 2 in wider than the shingle exposure (10 in x 7 in for a 5 in exposure).
- GAF Timberline HDZ (5-5/8 in exposure): 5 in on the roof, 5 in up the wall, pieces overlapping 2 in, so each piece runs at least 7-5/8 in along the slope.
- One piece per shingle course, woven into the course above, nailed with 2 nails within 1 in of the top edge of the roof leg (ARMA). Never nail the wall leg.
- Bottom piece gets a kickout flashing turning water into the gutter (IRC R903.2.1).
- Counter flashing (or siding lapped at least 2 in over the wall leg, per ARMA) covers the wall leg; never rely on sealant alone.
- Top piece tucks under headwall flashing or counter flashing at the top of the run.
Decision table: which step flashing detail fits your wall
Pick the row that matches your shingle and wall cladding. Each threshold traces to the 2021 IRC (as printed in the Seattle Residential Code, Chapter 9), the ARMA Residential Asphalt Roofing Manual or the shingle maker’s sheet.
| If | Then | Source |
|---|---|---|
| Shingle exposure is 5 in | Pieces at least 10 in x 7 in, bent 5 in / 5 in, overlapping 2 in | ARMA manual, Fig. 10-1 |
| Shingle exposure is 5-5/8 in (GAF Timberline HDZ) | Pieces at least 7-5/8 in along the slope with 5 in legs; an 8 in piece covers it | GAF HDZ instructions (2 in overlap) |
| Wall has lap siding | Wall leg runs continuously under the siding; siding laps at least 2 in over it and is not nailed into it | IRC R905.2.8.3; ARMA |
| Wall is anchored brick or stone veneer | Step flashing plus counterflashing set into the masonry | IRC R905.2.8.3, R703.8.2.2 |
| Wall is stucco or adhered stone | Step flashing plus the plaster or adhered veneer flashing detail | IRC R905.2.8.3, R703.6.3 |
| Roof eave meets the wall | Kickout (diverter) flashing at the bottom piece | IRC R903.2.1 |
| Chimney wider than 30 in across the slope | Step flashing on the sides plus a cricket on the ridge side | IRC R903.2.2 |
| Dormer front wall meets a sidewall | Cut the apron flashing to extend at least 7 in around the corner, then step flash up the side | ARMA manual |
What step flashing is and where it goes
Step flashing handles the wall-to-roof transition where a sloped roof butts against a vertical wall: a chimney side, a dormer side, a second-story wall above a porch roof, or a section of cladding on a multi-gable home. ARMA’s manual calls sheet metal step flashing placed under each course the best protection for “shingled roof planes that terminate against walls.” Water running down the wall tries to push behind the shingles, and water running down the shingles tries to push up behind the cladding; step flashing gives water a metal surface to track over, course by course.
The geometry matters. Each piece overlaps the one below by 2 inches (ARMA and GAF), is covered completely by the end shingle of the next course, and has its wall leg covered by counter flashing, siding lapped at least 2 inches, or stucco. The lap of the metal is the seal; GAF’s detail sets the overlying shingle into asphalt plastic cement on the flashing, and ARMA warns that excess cement causes blistering, so sealant is a supplement and not the primary seal.
For where flashing sits on a roof, see what is flashing on a roof and the roof flashing guide.
Our chimney flashing installation guide pairs step flashing with counter flashing and a cricket, which IRC R903.2.2 requires on chimneys wider than 30 inches. Low-slope roofs ending at a wall use our parapet wall flashing detail.
Step flashing size chart
How long is step flashing? Long enough along the slope to cover one shingle exposure plus a 2 inch overlap. ARMA’s rule is a piece at least 10 inches long, bent 90 degrees into a 5 inch roof leg and 5 inch wall leg, and at least 2 inches wider than the exposure. That gives 7 inches for a 5 inch exposure and 7-5/8 inches for the 5-5/8 inch exposure on GAF Timberline HDZ, so 8 inch pieces are the safe stock size for most architectural shingles.
| Rule or product | Wall leg | Roof leg | Length along slope | Metal | Source |
|---|---|---|---|---|---|
| IRC minimum (asphalt shingle sidewall) | 4 in | 4 in | Not set by code | At least 0.019 in (No. 26 galvanized) | IRC R905.2.8.3, R903.2.1 |
| ARMA, 5 in shingle exposure | 5 in | 5 in | 7 in | Sheet metal | ARMA manual Ch. 10 |
| GAF Timberline HDZ, 5-5/8 in exposure | 5 in | 5 in | At least 7-5/8 in (2 in overlap) | Noncorroding metal | GAF HDZ instructions |
| Gibraltar galvanized step flashing (model SF358G-25) | Listed as 5 in x 8 in, 25-pack | Check legs against the 4 in x 4 in minimum | Galvanized steel | Home Depot listing, Oct 2026 | |
| Gibraltar galvanized step flashing (model 964FRM-10) | Listed as 5 in x 7 in, 10-pack | Fits 5 in exposure | Galvanized steel | Home Depot listing, Oct 2026 | |
| Amerimax mill finish aluminum (model 85068) | Listed as 5 in x 7 in | Fits 5 in exposure | Aluminum | Home Depot listing, Oct 2026 | |
The length-along-slope number is what matters for ordering: shingle exposure plus 2 inches. Count one piece per course, so a sidewall that rises 10 feet along the slope takes about 23 pieces at a 5-5/8 inch exposure (120 inches divided by 5.625, rounded up, plus one for the kickout course). Retail listings give flat or folded sizes inconsistently, so confirm each leg is at least 4 inches before you buy.
Material comparison
Galvanized steel, aluminum, copper, and stainless are the common step flashing materials. The IRC sets a floor of corrosion-resistant metal at least 0.019 inch thick (No. 26 galvanized) for base flashing (R905.2.8.1), and the choice above that is about corrosion: step flashing buried behind siding or counter flashing cannot be inspected or replaced without removing the cladding, so pick the metal that suits the exposure and the neighboring metals.
| Material | Spec | Best for | Watch out for |
|---|---|---|---|
| Galvanized steel | ASTM A653, G90 coating (0.90 oz zinc per sq ft, both sides), 26 ga (0.019 in) | Standard residential, asphalt shingle, painted siding | White rust streaking on the wall; salt air shortens coating life |
| Aluminum | ASTM B209 sheet, 3003 or 5052 alloy, at least 0.019 in | Coastal, standard residential, stucco siding | Avoid contact with copper, pressure-treated lumber, and fresh concrete or mortar |
| Painted aluminum (Kynar 500 / PVDF) | ASTM B209, at least 0.019 in | Visible installations where color matters | Field cuts expose unpainted edges |
| Copper | ASTM B370, 16 oz (about 0.0216 in) | Premium residential, slate, cedar shake | Cost; stains wood and stucco below; keep away from aluminum and galvanized |
| Lead-coated copper | ASTM B370 base, 16 oz | Heritage work where copper staining is a concern | Cost; weight |
| Stainless steel | 304 (inland), 316 (coastal), 26 ga | Coastal, salt-air exposure, premium | Cost; harder to bend in the field |
Match fasteners to the metal: copper nails with copper, stainless or aluminum with aluminum. See our nails for flashing chart.
Pre-formed pieces such as Gibraltar’s 5 by 8 inch galvanized or Amerimax’s 5 by 7 inch aluminum save time on a job with standard exposures. On non-standard exposures or slate and shake roofs, field-bend pieces on a sheet metal brake to exposure plus 2 inches.
Step flashing installation sequence (5 steps)
Install step flashing from the bottom up, one piece per shingle course. Run the leak barrier up the wall, set the kickout flashing first, then weave each shingle course with a single step flashing piece, lapped 2 inches and nailed high on the roof leg only. Cover the wall legs with counter flashing or siding, and tuck the top piece under the headwall flashing.
- Step 1: Prep the substrate and run ice and water shield up the wall. Remove or lift the bottom course of siding so you can reach the wall sheathing. GAF’s Timberline HDZ detail extends GAF leak barrier at least 5 inches up the wall; ARMA’s minimum is underlayment carried 3 to 4 inches up the sidewall. Install starter shingle along the eave per the manufacturer’s spec. Do not caulk the wall-to-deck joint; water that gets behind the flashing needs a path back out.
- Step 2: Install kickout flashing at the bottom. IRC R903.2.1 requires a flashing “to divert the water away from where the eave of a sloped roof intersects a vertical sidewall.” The kickout turns that water into the gutter rather than down the wall, where it would run behind the cladding. See our dedicated kickout flashing guide for the geometry. Install the kickout first; everything above it laps onto it.
- Step 3: Set the first step flashing piece over the starter strip. ARMA places the first unit over the end of the starter strip so the end shingle of the first course covers it completely. Fasten the roof leg with two nails within 1 inch of the upper edge (GAF’s HDZ detail also shows 2 nails per piece). Never nail the wall leg: ARMA notes that differential movement between wall and roof will buckle shingles or break the seal.
- Step 4: Weave each shingle course with one step flashing piece. Lay the shingle course to the wall, then set the next piece over the end shingle at the exposure line (5 inches up for a 5 inch exposure, 5-5/8 inches for GAF HDZ) so the next course covers it completely. Each piece overlaps the one below by 2 inches. Continue: shingle, flashing, shingle, flashing, all the way up the wall. One piece per course, never a continuous strip.
- Step 5: Cover wall legs with counter flashing, siding, or stucco. On wood or fiber-cement siding, bring the siding down at least 2 inches over the wall legs (ARMA), do not nail it into the flashing, and hold it off the shingles by the siding maker’s clearance. On anchored brick or stone, set counter flashing into the masonry per IRC R703.8.2.2, with sealant in the reglet only. At the top of the run, the last piece tucks under the headwall (apron) flashing or counter flashing.
Common failure modes
Most step flashing failures come from five mistakes: a continuous strip instead of stepped pieces, a missing kickout at the bottom, reverse-shingled flashing, nails through the wall leg, and caulk used as the primary seal. None is fixed by IRC R905.2.8.3 alone, which allows continuous flashing. Each one lets water track behind the wall cladding, where it wets sheathing and framing before a roof leak shows. The full list is below.
- Continuous strip flashing instead of step flashing. A single piece of L-flashing running the full length of the wall is faster, but with no shingle weave breaking the path, water on the strip can track along the wall. The 2021 and 2024 IRC (R905.2.8.3) allow continuous or step base flashing at sidewalls, so a continuous strip is not by itself a model-code violation; it can still fail inspection where the shingle maker’s instructions call for step flashing, because R905.2.8 requires flashing to follow those instructions.
- No kickout at the bottom. Water runs off the bottom of the wall-to-roof junction and behind the siding, wetting the sheathing below the eave line. IRC R903.2.1 requires the diverter flashing for this reason.
- Reverse-shingled flashing. Each piece sits on top of the shingle in its course rather than under the shingle above, the opposite of ARMA Fig. 10-1. Water tracks behind the wall leg and into the wall.
- Nailing through the wall leg. ARMA says not to nail the vertical flange, because wall and roof move differently; each nail becomes a leak path.
- Caulk as primary seal. Sealant between the wall leg and the cladding is a backup, not a seal. If the 2 inch metal laps are not watertight without caulk, the install is wrong.
- Step flashing buried under stucco with no plaster flashing detail. Stucco cracks at metal transitions; IRC R905.2.8.3 sends plaster walls to R703.6.3 for the added flashing detail.
- Galvanic corrosion. Aluminum under copper counter flashing, or copper on galvanized, corrodes the aluminum or zinc when wet.
- Step flashing reused on a reroof. Old pieces carry nail holes from the previous layout, may not match the new shingle’s exposure (5-5/8 inches on GAF HDZ), and are often bent. Spec new flashing on every reroof.
- Skipping the leak barrier behind the flashing in cold climates. Ice dams push water up behind shingles. GAF’s detail runs leak barrier at least 5 inches up the wall, and IRC R905.1.2 requires an ice barrier at least 24 inches inside the exterior wall line where ice damming is designated.
- Bottom piece cut short. The IRC R903.2.1 kickout has to reach past the fascia line into the gutter; cut short, it dumps water on the fascia.
Most of these failures show up as stains on the interior side of the affected wall, not as roof leaks, because the water runs inside the wall cavity. The repair steps are in our roof flashing repair guide; the prevention is a correct 2 inch lap and kickout at install.
Cost
Step flashing material is a small line item next to HomeGuide’s $200 minimum repair figure; the cost driver is labor and access to the siding or masonry above it. On a full reroof, step flashing is normally priced inside the per-square shingle bid, so ask whether new flashing is included. HomeGuide’s 2026 cost guides give these ranges for repair work:
| Job | Typical cost | Source |
|---|---|---|
| Minor roof flashing repair | $200 to $500 | HomeGuide roof flashing repair guide, 2026 |
| Major repair or complete flashing replacement | $500 to $1,500 | HomeGuide roof flashing repair guide, 2026 |
| Chimney flashing repair | $300 to $1,800 | HomeGuide chimney flashing repair guide, 2026 |
| Pre-bent step flashing, retail | About $10 to $100 per pack, depending on size and count | Home Depot step flashing category, Oct 2026 |
Ask a contractor to quote siding removal and reinstallation separately from the flashing, because that line moves a sidewall retrofit more than the metal does.
For the broader leak-source diagnosis, see our roof leak repair and how to fix a roof leak guides, and the drip edge installation detail for the eave termination that pairs with the bottom piece. The roof vent pipe boot is another common leak point worth checking on the same roof.
Code references and certifications
IRC R905.2.8.3 (Sidewall Flashing) is the controlling section for base flashing at sidewalls on asphalt shingle roofs. In both the 2021 and 2024 IRC it reads that base flashing against a vertical sidewall “shall be continuous or step flashing”, at least 4 inches high and 4 inches wide, directing water onto the roof or into the gutter, with the vertical leg continuous under any siding. R905.2.8 adds that flashing for asphalt shingles shall comply with the shingle manufacturer’s approved installation instructions, and R905.2.8.1 sets base flashing at corrosion-resistant metal of at least 0.019 inch. The kickout is a separate rule: R903.2.1 requires a flashing to divert water away from where the eave of a sloped roof meets a vertical sidewall. (R905.2.8.5 is the drip edge section.) ASTM A653 is the spec for galvanized step flashing (G90 minimum is common). ASTM B209 is the spec for aluminum sheet (3003 or 5052 alloy). NRCA Roofing Manual: Steep-Slope Roofing details the residential step flashing standard. The step-flashing requirement itself comes from the shingle makers: GAF’s Timberline HDZ instructions detail metal step flashing at sloped-roof-to-wall intersections, and Owens Corning’s Duration STORM and FLEX instructions call for step flashing where the roof meets vertical sidewalls or chimneys. Installing against the maker’s instructions can affect warranty coverage, so check the warranty for the shingle line.
Frequently asked questions
What size step flashing should I use?
Make each piece shingle exposure plus 2 inches long along the slope, with legs of at least 4 inches (IRC R905.2.8.3). ARMA’s standard is 10 by 7 inches bent 5 and 5 for a 5 inch exposure; GAF Timberline HDZ, at a 5-5/8 inch exposure, needs at least 7-5/8 inches, so 8 inch pieces fit.
How long is step flashing?
Along the slope, step flashing is the shingle exposure plus a 2 inch overlap: 7 inches for a 5 inch exposure (ARMA) and at least 7-5/8 inches for a 5-5/8 inch exposure (GAF Timberline HDZ). Retail packs are listed as 5 by 7 inches and 5 by 8 inches, such as Gibraltar’s SF358G-25.
Can I use one continuous piece instead of stepped pieces?
Not on a shingle roof, if you follow the shingle maker. The 2021 and 2024 IRC (R905.2.8.3) allow continuous or step base flashing at sidewalls, but asphalt shingle manufacturers such as GAF and Owens Corning show step flashing at roof-to-wall intersections, and R905.2.8 requires flashing to follow their instructions. Use one piece per shingle course so each course sheds water onto the shingle below.
Do I need a kickout flashing at the bottom of the step flashing run?
Yes. Without a kickout, water running off the bottom of the wall-to-roof junction goes behind the siding and wets the framing. The kickout turns that water into the gutter instead. IRC R903.2.1 (2021 and 2024) requires a flashing to divert water away from where the eave of a sloped roof meets a vertical sidewall.
What material should I use for step flashing?
Use corrosion-resistant metal at least 0.019 inch thick, which is No. 26 galvanized (IRC R905.2.8.1). Standard residential: G90 galvanized steel or aluminum. Coastal: aluminum or 316 stainless. Slate or cedar shake: 16 oz copper (ASTM B370) or stainless. Keep copper away from aluminum and galvanized steel.
How long does step flashing last?
No shingle maker or code publishes a service life for step flashing, so pick the metal by exposure: G90 galvanized or aluminum for most inland homes, stainless or aluminum near salt air, 16 oz copper or stainless where the roof covering itself lasts decades, such as slate. Because replacing it means removing siding, use new flashing at every reroof.
Can I replace step flashing without removing the siding?
Almost never. The IRC requires the wall leg to run continuously under the siding, so the bottom courses of siding above the flashing run have to come off. The exception is masonry with a separate counter flashing set in a reglet, where the counter flashing can be removed and reset.
Bottom line
Step flashing is the cheapest wall-junction protection on the roof: HomeGuide’s 2026 repair ranges start at $200 to $500, while the metal for one wall is a single retail pack. Spec it correctly: stepped, not continuous; one piece per shingle course at exposure plus 2 inches; legs of at least 4 inches (5 inches on GAF’s detail); a kickout at the bottom per IRC R903.2.1; siding or counter flashing lapped at least 2 inches over the wall leg; and leak barrier at least 5 inches up the wall.