Roof-to-Wall Flashing Calculator

Calculate step flashing piece count, kick flashing length, and material costs for roof-to-wall junctions on sidewalls and headwalls

Calculate step flashing pieces for sidewall roof-to-wall junctions

Quick presets

feet

Flashing Needed

20 LF

20 linear feet of coverage

PRO

Professional Calculator

Extended parameters for precise calculations

sq ft

Estimated Materials

60 bundles

Roof Area

1,792 sq ft

Squares

17.9

Detailed Breakdown

Roof Area1,792 sq ft
With Waste1,971 sq ft
Roofing Squares17.9
Bundles60
How to Use This Calculator
The Roof-to-Wall Flashing Calculator helps you determine the exact quantity of step flashing pieces, kick flashing sections, and sealant needed for every type of roof-to-wall junction on your project.

Step Flashing tab: Enter the sidewall junction length (measured along the roof slope where it meets the wall), your shingle course exposure (5 inches is standard for architectural shingles), and select the flashing piece size and material. The calculator divides the wall length by the shingle exposure to determine how many individual step flashing pieces you need, then adds a waste factor. If you have multiple sidewall junctions — for example, two sides of a dormer or two separate sidewall runs — enter the number of junctions and the calculator multiplies accordingly. The material selector shows 2026 pricing per piece for aluminum, galvanized steel, copper, and lead.

Kick Flashing tab: Enter the headwall length where a roof slope terminates against a vertical wall. Select the kick flashing profile (standard L, extended L, or Z-bar for siding integration) and material. The calculator determines how many stock-length sections you need, accounting for 3-4 inch overlap at each joint. For a 30-foot headwall using 10-foot sections, you need 4 sections (with 3 overlap joints consuming about 10 inches total). This tab is essential for headwall transitions, which are the most leak-prone areas on any roof.

Cost tab: Enter the total combined junction length, select your material grade, and choose the installation type — new construction, re-roofing, or retrofit. New construction is cheapest because flashing installs before siding. Re-roofing requires siding removal and reinstallation, adding $5-$15 per linear foot in labor. Retrofit surface-mounting is the cheapest but provides the weakest seal and is not recommended for permanent installations. The cost estimate includes flashing material, sealant, ice and water shield membrane at the junction, and labor adjusted for your state.

The Formula
The roof-to-wall flashing calculator uses these formulas:

Step Flashing Piece Count = (Wall Length in inches / Shingle Course Exposure) + 1 Example: 20 ft × 12 = 240 inches; 240 / 5" exposure = 48 + 1 starter = 49 pieces

Step Flashing Material Cost = Piece Count × Cost per Piece Example (aluminum): 49 × $0.75 = $36.75

Kick Flashing Sections = ceil(Headwall Length / (Section Length - Overlap)) Overlap = 3 inches per joint Example: 30 ft headwall / (10 ft - 0.25 ft) = 30 / 9.75 = 4 sections (rounded up)

Kick Flashing Material Cost = Sections × Section Length × Cost per Linear Foot Example (galvanized): 4 × 10 ft × $4.00/LF = $160.00

Sealant Tubes = Total Junction Length / 15 (1 tube per 15 linear feet) Example: 30 ft / 15 = 2 tubes × $8/tube = $16

Total Labor Cost = Total Junction Length × Labor Rate per LF - New construction: $5-$10/LF - Re-roofing: $10-$20/LF (includes siding removal/reinstall) - Retrofit: $3-$8/LF

Total Project Cost = Material + Sealant + Labor + Ice & Water Shield ($0.50-$1.00/LF)
Example Calculation
Example: Dormer Reflashing During Re-Roof — Two Sidewalls + One Headwall in Ohio

Maria is having her roof replaced and wants to properly reflash a shed dormer that has been leaking. The dormer has two 16-foot sidewalls and one 10-foot headwall.

Step 1: Step Flashing (2 sidewalls)
• Each sidewall: 16 ft = 192 inches
• Shingle exposure: 5" (standard architectural)
• Pieces per sidewall: 192 / 5 + 1 = 39.4 → 40 pieces
• Total for 2 sidewalls: 40 × 2 = 80 pieces
• Material (aluminum at $0.75/piece): 80 × $0.75 = $60.00

Step 2: Kick Flashing (1 headwall)
• Headwall: 10 ft
• Using 10-foot sections: 1 section needed (no joints)
• Material (galvanized extended L at $4.50/LF): 10 × $4.50 = $45.00

Step 3: Sealant & Accessories
• Total junction length: 16 + 16 + 10 = 42 feet
• Sealant tubes: 42 / 15 = 3 tubes × $8 = $24.00
• Ice & water shield at junctions: 42 LF × $0.75/LF = $31.50

Step 4: Labor (re-roofing — siding removal included)
• Labor rate in Ohio: $12/LF for re-roofing with siding removal
• 42 LF × $12 = $504.00

Total dormer reflashing cost: $664.50 This is included in Maria's full re-roof, but as a standalone repair it would cost $900-$1,200 due to minimum service charges.

Frequently Asked Questions

What is the difference between step flashing and kick flashing on a roof?
Step flashing and kick flashing serve different purposes at roof-to-wall junctions. Step flashing is used on sidewalls where the roof slope runs parallel to the wall — individual L-shaped pieces are woven between each shingle course so water cascades down from piece to piece rather than pooling behind the shingles. Each piece overlaps the one below it by the shingle exposure distance. Kick flashing (also called headwall flashing or apron flashing) is a single continuous piece used where the roof slope terminates against a vertical wall, such as where a lower roof meets a second-story wall. The kick flashing diverts water flowing down the roof away from the wall-roof junction. Both are critical for preventing water intrusion, which is the leading cause of roof-to-wall leak failures.
How many step flashing pieces do I need per foot of wall?
The number of step flashing pieces depends on your shingle course exposure. With standard architectural shingles at 5-inch exposure, you need one piece per 5 inches of wall length, which works out to 2.4 pieces per linear foot — so a 20-foot sidewall requires 48 pieces. For 3-tab shingles at 5-inch exposure, the count is the same. Wood shakes with 7-inch exposure require approximately 1.7 pieces per foot. Slate or tile at 10-inch exposure requires about 1.2 pieces per foot. Always add 5-10% extra to your count for waste, starter and termination pieces, and mistakes. In 2026, pre-bent step flashing pieces come in boxes of 50 or 100 and cost $25-$50 per box for aluminum.
Should roof-to-wall flashing go under or over the siding?
Roof-to-wall flashing must always go under the siding and building wrap (house wrap like Tyvek), never over it. The correct weatherlap sequence from inside to outside is: sheathing, house wrap, flashing wall leg tucked under house wrap, flashing roof leg over shingles (for step flashing) or over underlayment (for kick flashing). If the flashing is installed over the siding, water running down the wall face will channel behind the flashing and into the wall cavity, causing rot and mold. During re-roofing, this means the bottom 1-2 courses of siding must be carefully removed, the old flashing stripped, new flashing installed under the house wrap, and the siding reinstalled. This adds labor cost but is the only method that provides a proper weatherproof seal.
What material is best for roof-to-wall flashing in 2026?
For most residential applications in 2026, aluminum step flashing is the best value at $0.50-$1.00 per piece, offering corrosion resistance, easy bending, and 30-40 year lifespan. Galvanized steel ($0.75-$1.50/piece) is stronger and preferred in areas with heavy snow loads but can rust after 20-30 years if the galvanized coating is scratched. Copper ($3-$6/piece) is the premium choice with 70+ year lifespan and is standard on historic restorations, slate roofs, and high-end homes — it develops an attractive green patina over time. Lead flashing ($2-$4/piece) is exceptionally malleable and self-healing but is increasingly restricted due to environmental regulations. For most homeowners replacing an asphalt shingle roof, aluminum provides the best balance of durability, cost, and ease of installation.
How much does it cost to reflash a roof-to-wall junction in 2026?
The cost to reflash a roof-to-wall junction ranges from $15-$50 per linear foot in 2026, depending on material choice, installation complexity, and your state. A typical 20-foot dormer sidewall with aluminum step flashing costs $300-$600 for materials and labor when done during a re-roofing project. If reflashing is done as a standalone repair, expect $500-$1,200 because the roofer must remove and replace shingles and siding to access the junction. Copper flashing roughly triples the material cost. The labor portion is $200-$500 per junction for removing siding, installing flashing with proper weatherlap, and reinstalling siding. Always get the reflashing done during a full re-roof when possible — it is far cheaper when the shingles are already off than as a separate repair visit.

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