Chimney Flashing Calculator

Calculate chimney flashing materials including step flashing, counter flashing, base flashing, cricket dimensions, and total cost by chimney size and roof pitch

Get a fast material list based on chimney size and roof pitch

Quick presets

inches
inches

Flashing Needed

40 LF

40 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 Chimney Flashing Calculator determines exactly what materials you need to properly flash a chimney penetration, from step flashing pieces to counter flashing and cricket components.

Quick Estimate tab: Enter your chimney width (measured across the slope) and depth (measured along the slope), select your roof pitch, and choose a flashing material. The calculator instantly determines how many step flashing pieces you need for both sides, the linear feet of counter flashing for the front apron and rear wall, and whether a cricket is required based on chimney width. This gives you a fast shopping list and material cost estimate.

Detailed Materials tab: This tab adds precision by letting you specify whether a cricket is needed, whether you want ice and water shield membrane around the chimney, and the exact flashing material. The calculator generates a complete bill of materials: step flashing count and size, counter flashing linear footage, base/apron flashing dimensions, cricket plywood and flashing, ice and water shield square footage, sealant tubes, and roofing cement. Use this list when ordering materials or getting contractor quotes.

Project Cost tab: The cost tab brings it all together with a full estimate including materials, labor, and the cost of removing existing flashing. Labor costs are adjusted by state, and the calculator accounts for whether this is a full replacement, a repair, or new construction. It also factors in the difficulty premium for steep pitches, which increases labor time and safety equipment needs.

The Formula
The chimney flashing calculator uses these formulas:

Step Flashing Count = (Chimney Depth / Shingle Exposure) + 1, per side, x 2 sides - Standard shingle exposure: 5 inches (5-5/8" for architectural) - Example: 24" depth / 5" exposure = 4.8 → 5 pieces + 1 extra = 6 per side x 2 = 12 step flashing pieces

Counter Flashing (linear feet) = Chimney Width (front apron) + Chimney Width (rear) + Chimney Depth x 2 (sides) - Front apron: Chimney Width + 8" (4" overlap each side) - Rear: Chimney Width + 8" - Sides: covered by step flashing counter (integrated or separate) - Example: 36" wide, 24" deep → (36+8) + (36+8) + (24+8) x 2 = 44 + 44 + 64 = 152" = ~13 LF counter flashing

Cricket Required = Yes if chimney width > 30 inches Cricket Ridge Length = Chimney Width / 2 Cricket Area = (Chimney Width x Cricket Ridge Length) / 2 - Example: 42" chimney → Cricket ridge = 21", Area = (42 x 21) / 2 = 441 sq in = ~3.1 sq ft

Ice & Water Shield = Perimeter of chimney + 24" beyond each side - Area = (Chimney Width + 48") x (Chimney Depth + 48") - (Chimney Width x Chimney Depth)

Total Material Cost = Step flashing + Counter flashing + Apron + Cricket materials + Ice shield + Sealant Total Project Cost = Materials + Labor ($300-$800 per chimney) + Tear-off (if replacement)
Example Calculation
Example: 42"x30" Chimney with Cricket — Galvanized Steel Flashing in Ohio

Tom is replacing the flashing on a 42-inch-wide by 30-inch-deep masonry chimney on his 5/12-pitch roof in Columbus, Ohio. The chimney is wider than 30 inches, so a cricket is required by code.

Step 1: Quick Estimate
• Chimney: 42" wide x 30" deep, 5/12 pitch
• Step flashing pieces: (30" / 5" exposure) + 1 = 7 pieces per side x 2 sides = 14 step flashing pieces
• Counter flashing: front apron (42" + 8" = 50") + rear (50") + side caps = ~10 LF
• Cricket required: Yes (42" > 30" threshold)

Step 2: Detailed Material List
• 14x galvanized step flashing (5x7"): 14 x $4 = $56
• 10 LF galvanized counter flashing (bent to profile): 10 x $5/LF = $50
• 1x front apron (pre-bent, 50" long): $25
• Cricket plywood (1/2" CDX, ~4 sq ft): $8
• Cricket metal flashing (galvanized sheet): $35
• Ice and water shield (extends 24" beyond chimney on all sides): ~28 sq ft = $28
• Polyurethane sealant (2 tubes): $18
• Roofing cement (1 qt): $8
• Total materials: ~$228

Step 3: Full Project Cost
• Materials: $228
• Tear-off old flashing and clean mortar joints: $150
• Labor — install step flashing, counter flashing, apron, and cricket: $550
• Re-shingle around chimney area: $125
• Total installed: $1,053

Tom's new cricket-and-flashing system will properly divert water around his chimney, preventing the recurring leak he experienced every spring. The galvanized steel will last 25-30 years — matching his architectural shingle roof life.

Frequently Asked Questions

How much does chimney flashing cost to replace in 2026?
A full chimney flashing replacement with standard aluminum or galvanized steel costs $300-$800 for materials and labor on a typical 30x24-inch chimney. This includes step flashing on both sides, a front apron, rear counter flashing, and sealant. Copper flashing raises the material cost significantly — expect $800-$1,500 total for the same chimney with copper. If a cricket is needed (chimney wider than 30 inches), add $200-$600 for the cricket frame, sheathing, and flashing. Most roofers charge $300-$500 in labor for a straightforward flashing replacement, though steep pitches and difficult access can push labor to $500-$800.
When does a chimney need a cricket (saddle)?
Building codes (IRC R903.2.2) require a cricket when the chimney width on the upslope side exceeds 30 inches. The cricket is a small peaked diverter built behind the chimney that prevents water and debris from pooling against the masonry. Even on chimneys narrower than 30 inches, a cricket is highly recommended in regions with heavy snowfall or leaf debris. Without a cricket, water backs up behind the chimney, accelerates flashing deterioration, and can cause leaks within 5-10 years. Cricket construction involves building a small plywood frame, covering it with ice and water shield, then applying metal flashing over the top. Materials cost $100-$250 and labor adds $150-$350.
What is the difference between step flashing and counter flashing?
Step flashing consists of small L-shaped metal pieces (typically 4x4 inches or 5x7 inches) woven into each course of shingles along the sides of the chimney. Each piece overlaps the one below it, creating a stair-step pattern that channels water away from the chimney-to-roof junction. Counter flashing is a continuous piece of metal set into the mortar joints of the chimney that folds down over the top edge of the step flashing. It acts as a cap, preventing water from getting behind the step flashing. Both layers work together — step flashing handles primary drainage while counter flashing seals the top edge against wind-driven rain.
Should I use copper or aluminum chimney flashing?
Aluminum is the budget-friendly choice at $3-$5 per step flashing piece and lasts 20-30 years with proper installation. It corrodes when in direct contact with masonry mortar, so a barrier layer or caulk is recommended. Copper costs 3-4 times more ($8-$15 per linear foot for counter flashing) but lasts 80-100+ years, does not corrode against masonry, and develops a distinctive green patina. For a roof with a 30-year shingle, aluminum is perfectly adequate since you will replace the flashing with the next re-roof. For a slate, tile, or copper roof that lasts 50-100 years, copper flashing is the only sensible choice to avoid premature flashing replacement.
How many pieces of step flashing do I need for my chimney?
You need one step flashing piece for each course of shingles along each side of the chimney, plus 1-2 extra per side. With standard shingles having a 5-inch exposure, a chimney that is 24 inches deep along the slope requires about 5-6 step flashing pieces per side (24 / 5 = 4.8, rounded up to 5, plus 1 extra). For both sides, that means 10-12 pieces total. Step flashing pieces are typically 4x4, 5x7, or 8x8 inches — the larger sizes are easier to work with and provide better coverage. Always buy 2-3 extra pieces to account for cuts and fitting. A 10-pack of aluminum 5x7 step flashing costs approximately $15-$25 at major home centers.

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