Roof Cricket Calculator

Calculate cricket (saddle) dimensions behind a chimney or wall intersection — height, valley length, plywood area, and material costs per IRC R903.2.2 requirements

Calculate cricket height, valley length, and footprint from chimney width and roof pitch

Quick presets

inches

Count

27 pieces

24" spacing • 16.1 ft length

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 Cricket Calculator helps you determine whether your chimney needs a cricket, what size it should be, and how much it will cost to build. A missing or undersized cricket is one of the most common causes of chimney-related roof leaks, yet many homeowners and even some contractors overlook this critical detail. If your chimney is wider than 30 inches, a cricket is required by the IRC and should be a non-negotiable part of any re-roof or chimney project.

Dimensions tab: Enter your chimney width (measured across the roof slope), roof pitch, and desired cricket pitch. Matching the cricket pitch to the roof pitch is standard practice — it provides the best water shedding and the most natural appearance. The calculator outputs the cricket peak height, valley line length, and footprint area. The chimney location selector adjusts recommendations: a chimney near the eave collects more upslope water and benefits from a taller cricket and more aggressive ice protection. If your chimney is 30 inches or less in width, the calculator will note that a cricket is not code-required but may still be recommended.

Materials tab: This tab generates a complete materials list for building the cricket. Enter the chimney width and calculated height, then select your framing type, flashing material, and ice shield coverage. The output includes plywood square footage, lumber linear feet, step flashing piece count, counter flashing length, ice shield area, and shingle quantity. For most standard chimneys, the materials cost is under $200 — the majority of the cricket cost is labor. The pre-fabricated metal option eliminates most material items and replaces them with a single factory-built unit.

Cost Estimate tab: This tab provides a total installed cost estimate for your cricket. The cost varies significantly based on three factors: the construction type (framed vs. pre-fab vs. custom copper), access difficulty (roof pitch and height), and whether the cricket is built during a re-roof or as a standalone repair. A standard framed cricket built during a re-roof adds $500-$1,000 to the project. The same cricket as a standalone job costs $800-$2,000 because of the additional setup, tear-in, and integration work. The calculator adjusts for your state's labor rates.

The Formula
The roof cricket calculator uses these formulas:

Cricket Peak Height Height = (Chimney Width / 2) × tan(Cricket Pitch Angle) For pitch expressed as rise/run: Height = (Chimney Width / 2) × (Rise / Run) Example: 36" chimney, 5/12 cricket pitch → (36/2) × (5/12) = 18 × 0.417 = 7.5 inches

Cricket Valley Line Length Valley = √((Chimney Width / 2)² + Height²) Example: √(18² + 7.5²) = √(324 + 56.25) = √380.25 = 19.5 inches (1.63 ft)

Cricket Surface Area (both faces) Area = Chimney Width × Valley Length (approximation for the two triangular faces) Example: 36" × 19.5" = 702 sq in = 4.9 sq ft

Plywood Needed Plywood = Cricket Surface Area × (1 + Waste%) Example: 4.9 sq ft × 1.15 = 5.6 sq ft (less than a quarter sheet of 4×8 plywood)

Step Flashing Pieces Pieces = (Valley Length × 2 sides) / Shingle Exposure + 2 extra Standard exposure = 5.625" for architectural shingles Example: (19.5" × 2) / 5.625" + 2 = 6.9 + 2 = 9 step flashing pieces

Counter Flashing Length Counter Flash = Chimney Width + (2 × Cricket Valley Length projected onto chimney face) Example: 36" + (2 × ~10") = 56 inches ≈ 5 linear feet
Example Calculation
Example: 36-Inch Chimney Cricket — Built During a Re-Roof in Pennsylvania

Karen is getting a full re-roof on her two-story colonial in Pennsylvania. The chimney is 36 inches wide (3 feet across the slope) at mid-slope on the back roof plane. The roof pitch is 6/12. The existing cricket is deteriorated and the plywood behind the chimney has water damage.

Step 1: Cricket Dimensions
• Chimney width: 36 inches
• Cricket pitch: match roof at 6/12
• Cricket height = (36/2) × (6/12) = 18 × 0.5 = 9.0 inches
• Valley length = √(18² + 9²) = √(324 + 81) = √405 = 20.1 inches (1.68 ft each)
• Cricket footprint: 36" wide × 20.1" deep = approximately 5.0 sq ft total surface

Step 2: Materials List
• 2x4 lumber (ridge + valleys): 2 pieces × 4 ft = 8 linear feet ($8)
• 1/2" plywood sheathing: 5.0 × 1.15 waste = 5.75 sq ft (quarter sheet) ($15)
• Ice & water shield (full cricket + 3 ft upslope): 12 sq ft ($18)
• Step flashing pieces (5×7" aluminum): (20.1 × 2) / 5.625 + 2 = 9 pieces ($18)
• Counter flashing (aluminum): 5 linear feet ($12)
• Matching architectural shingles: ~6 sq ft (from field bundle, $0 incremental)
• Roofing cement and sealant: ($8)
• Total materials: ~$79

Step 3: Labor Cost (during re-roof, moderate difficulty)
• Cricket framing and sheathing: 1.5 hours
• Ice shield application: 0.5 hours
• Flashing installation: 1.0 hours
• Shingling the cricket: 0.5 hours
• Total labor: 3.5 hours × $65/hr = $228

Step 4: Total Cricket Cost
• Materials: $79
• Labor: $228
• Damaged decking repair behind chimney (3 sq ft plywood replacement): $45
• Total: $352 (added to the re-roof contract)

If this were a standalone repair (not during a re-roof), the cost would approximately double to $700-$900 due to setup, material staging, and the complexity of tying into existing shingles.

Frequently Asked Questions

What is a roof cricket and when is it required by code?
A roof cricket (also called a saddle) is a small peaked structure built on the uphill side of a chimney or wall intersection to divert water around the obstruction instead of allowing it to pool behind it. Per IRC R903.2.2, a cricket or saddle is required on the ridge side of any chimney or penetration that is more than 30 inches wide measured perpendicular to the roof slope. This means any chimney wider than 30 inches must have a cricket. The code does not specify the cricket dimensions in detail, only that it must be covered with the same material as the surrounding roof or with metal flashing. In practice, the cricket should be tall enough to effectively divert water and snow — typically rising to a peak height equal to half the chimney width times the tangent of the cricket pitch angle.
How do I calculate the height and dimensions of a roof cricket?
The cricket peak height is calculated as: height = (chimney_width / 2) x tan(cricket_pitch_angle). For a 36-inch wide chimney with a cricket pitch matching a 5/12 roof: height = (36/2) x (5/12) = 18 x 0.417 = 7.5 inches. The cricket forms a triangle in plan view with the base equal to the chimney width and two valley lines running from each side of the chimney back to the peak. Each valley line length equals the square root of ((chimney_width/2)^2 + height^2). For our example: valley = sqrt(18^2 + 7.5^2) = sqrt(324 + 56.25) = sqrt(380.25) = 19.5 inches. The total surface area of the cricket (both sides of the saddle) is approximately chimney_width x valley_length / 2 x 2 = chimney_width x valley_length. For our example: 36 x 19.5 = 702 square inches or about 4.9 square feet.
What materials are needed to build a chimney cricket?
A standard framed cricket requires: 2x4 lumber for the ridge beam and valley rafters (typically 8-12 linear feet depending on chimney size); 1/2-inch or 5/8-inch plywood sheathing for the two sloped faces (4-10 square feet); ice and water shield membrane to cover the entire cricket surface; step flashing pieces (typically 5x7 inch aluminum or galvanized steel) — one per shingle course along each valley; counter flashing to embed in the chimney mortar or reglet; matching shingles to cover the cricket surface; and roofing nails and sealant. For a 36-inch chimney, a typical materials list is: two 8-foot 2x4s, a quarter sheet of plywood, 15 square feet of ice shield, 8-10 step flashing pieces, 6 feet of counter flashing, and about half a bundle of shingles. The total material cost is approximately $75-$150.
Can I install a pre-fabricated metal cricket instead of building one?
Yes, pre-fabricated metal crickets are an excellent option, especially for standard chimney sizes. They are available in aluminum, galvanized steel, and copper from companies like Batson Manufacturing and Metal Era. Pre-fab crickets come in standard widths (24, 30, 36, 42, and 48 inches) and adjustable pitch ranges. The main advantages are speed (installs in 30 minutes versus 2-4 hours for a framed cricket), reliability (factory-formed with no custom carpentry), and waterproofing (the cricket and flashing are one integrated piece). The disadvantages are that they may not visually match the surrounding shingles (metal vs. shingled surface), they are not available for non-standard chimney sizes, and they cost $150-$400 for the unit itself. For a straightforward chimney on a standard-pitch roof, a pre-fab metal cricket is often the best choice.
What happens if a chimney does not have a cricket when it should?
A chimney wider than 30 inches without a cricket creates a dam behind the chimney where water and debris accumulate. Over time, this trapped water penetrates beneath the shingles and flashing, causing rotted roof sheathing, damaged rafters, interior water stains, and potential mold growth in the wall cavity behind the chimney. In cold climates, the problem is amplified by ice dams: snow melting on the roof above the chimney freezes behind the chimney in a sheltered cold zone, creating a growing ice mass that forces water under the flashing and shingles. The repair cost for water damage caused by a missing cricket ranges from $2,000-$10,000 depending on severity — far more than the $500-$1,500 cost of installing a cricket. If your chimney is wider than 30 inches and lacks a cricket, adding one should be a top priority, ideally during your next re-roof.

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