Cedar Shake & Shingle Siding Calculator
Cedar sidewall coverage is driven by weather exposure, not board length — a bundle covers more wall at a wider exposure. This calculator uses the CSSB square/bundle coverage the same way estimators do: 4 bundles of #1 sawn shingles (5 of handsplit shakes) cover one square at the reference exposure, scaled to whatever exposure you set.
It handles single course (standard sidewall) and double course (the deep-shadow look), automatically adding an equal count of low-grade undercourse bundles for double-course walls, plus a corner allowance of roughly one square per 100 linear feet of corners.
Free, no signup. Installing polymer cedar-look shake panels (e.g. CertainTeed Cedar Impressions)? Those behave like vinyl — use the vinyl siding calculator instead.
Cedar Shake & Shingle Siding Calculator
Estimate bundles and squares of cedar sidewall shingles or shakes by weather exposure — single or double course, with corner allowance, coursing layout, and fasteners.
Walls
Enter each wall's width and height. Add the gable rise for triangular gable ends.
Add up every window and door opening. A 3'×5' window = 15 sq ft; a 3'×6'8" door = 20 sq ft.
Product & grade
Certi-label sawn shingles or handsplit shakes
Coursing & exposure
Exposure drives coverage — leave exposure blank to use the CSSB maximum
Blank = max single course (8.5"). Exposure over the grade-adjusted maximum is capped automatically and flagged in the notes.
Corners & complexity
Extra material for corners and cut-up walls
Corner length = sum of every inside and outside vertical corner. Woven/mitered corners add ~1 square per 100 LF.
Calculation Formulas
Every wall is a rectangle plus, where present, a gable triangle above the eave. Window and door openings are subtracted once as a single total.
Example:
Two 30 ft × 9 ft walls + two 24 ft × 9 ft walls − 120 sq ft openings = 852 sq ft net.
A bundle holds a fixed total shingle width, so coverage scales linearly with weather exposure. This one formula spans single and double coursing — double coursing is just a much wider exposure.
Example:
18" #1 Perfection at 5.5" → 25 sq ft/bundle; the same product at 14" double-course → 25 × (14 ÷ 5.5) = 64 sq ft/bundle.
Waste-adjusted area divided by per-bundle coverage, rounded up to whole bundles since cedar is sold by the bundle only.
Example:
852 sq ft × 1.10 ÷ 25 = 37.5 → 38 bundles at 5.5" single course.
Four bundles of #1 sawn shingles (five of handsplit shakes) equal one square — 100 sq ft of wall at the reference exposure.
Example:
38 bundles ÷ 4 = 9.5 squares.
Woven or mitered corners consume extra material; the CSSB/JLC field rule adds roughly one square per 100 linear feet of inside and outside corners.
Example:
80 LF of corners → (80 ÷ 100) × 4 = 3.2 → 4 corner bundles.
Dividing the wall into whole courses and back-solving the exposure keeps the top course from finishing as a thin sliver under the eave.
Example:
108 in ÷ 5.5 = 19.6 → 20 courses; 108 ÷ 20 = 5.4" even exposure.
Double coursing lays a cheap undercoursing shingle beneath each exposed course, so you need an equal count of #3/undercourse-grade bundles in addition to the #1 outer course.
Example:
38 outer bundles → 38 undercourse bundles.
Two corrosion-resistant nails per shingle work out to roughly two pounds of nails per square of single-course wall; double coursing raises the count.
Example:
9.5 squares single course → ceil(9.5 × 2) = 19 lb of stainless or hot-dipped nails.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Bundles per square — sawn shingles | 4 | Four bundles of #1 Blue Label sawn shingles cover one square (100 sq ft) at the reference exposure. |
| Bundles per square — handsplit shakes | 5 | Thicker handsplit & resawn shakes are packaged five bundles to the square. |
| Reference exposure — 18" shingle | 5.5 in | Exposure at which four bundles of 18" Perfection cover 100 sq ft. |
| Max single-course exposure — 18" | 8.5 in | CSSB maximum recommended single-course sidewall exposure for 18" #1 shingles. |
| Max double-course exposure — 18" | 14 in | CSSB maximum recommended double-course sidewall exposure for 18" #1 shingles. |
| #2 grade exposure factor | 0.85 | Red Label (#2) shingles carry ~15% less maximum exposure than #1 Blue Label. |
| Simple-wall waste | 10% | CSSB/JLC baseline waste for straight, uncomplicated walls; rises to 15–20% for gables and staggered courses. |
| Corner allowance | ≈1 square / 100 LF | Extra material for woven or mitered inside and outside corners. |
| Fastener rate | ≈2 lb / square | Two nails per shingle, corrosion-resistant only (ASTM A153 hot-dipped or stainless). |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
CSSB Exterior & Interior Wall Manual(CSSB Wall Manual)
View StandardThe Cedar Shake & Shingle Bureau sidewall coverage tables (single- and double-course), maximum-exposure tables, and application details this calculator is built on.
Key Requirements:
- •Sidewall coverage stated per square (4 bundles sawn / 5 bundles shake) at listed exposures
- •Maximum single- and double-course exposures by length and grade
- •Woven, mitered, and corner-board corner treatments
- •Certi-label #1 (Blue) and #2 (Red) grade definitions
IRC — Wood Shakes and Shingles (Wall Covering)(IRC R703.5)
View StandardInternational Residential Code requirements for wood shakes and shingles applied as exterior wall covering, including attachment and weather-exposure limits.
Key Requirements:
- •Shakes/shingles installed over a water-resistive barrier or approved sheathing
- •Two corrosion-resistant fasteners per shingle, concealed by the next course
- •Weather exposure within the manufacturer/CSSB maximum for the grade
IRC — Water-Resistive Barrier(IRC R703.2)
View StandardRequires a water-resistive barrier behind the exterior wall covering; the substrate cedar sidewall is fastened over.
Key Requirements:
- •Minimum one layer of an approved WRB (No. 15 felt or equivalent)
- •Shingled/lapped so water drains to the exterior
Corrosion-Resistant Fasteners(ASTM A153 / stainless)
View StandardCedar's natural extractives corrode ordinary steel; only hot-dipped galvanized (ASTM A153) or stainless fasteners are acceptable.
Key Requirements:
- •Hot-dipped galvanized (A153) or Type 304/316 stainless nails
- •Ring-shank preferred for withdrawal resistance
- •No electro-galvanized or bright steel (causes black streaking)
Certi-label Grading(CSSB Certi-label)
View StandardThe CSSB quality-certification program defining #1 Blue Label (premium), #2 Red Label, and undercoursing grades used in double coursing.
Key Requirements:
- •#1 Blue Label: 100% clear, 100% heartwood, 100% edge grain
- •#2 Red Label: proportion of flat grain and limited sapwood permitted
- •Undercoursing grade for the hidden layer in double coursing
Vented Rainscreen (best practice)(CSSB / FSC rainscreen guidance)
View StandardA ventilated air gap behind cedar sidewall dramatically improves dry-down and service life; widely recommended though not universally code-mandated.
Key Requirements:
- •Furring strips or a drainage/ventilation mat behind the shingles
- •Open top and bottom for airflow
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Wildfire / WUI zones
California, Colorado, mountain West
Wildland-Urban Interface codes may require fire-retardant-treated (Certi-guard) cedar or prohibit untreated wood cladding outright.
Regional Examples:
Coastal / high-humidity
Pacific Northwest, New England coast, Gulf
Persistent moisture makes a vented rainscreen and stainless (not just hot-dipped) fasteners the practical standard, and favors #1 all-heartwood stock.
Regional Examples:
Cold / snow-load climates
Upper Midwest, Mountain, Northeast
Tighter single-course exposures shed snow-melt better and reduce ice intrusion at the butt lines.
Regional Examples:
Hot-dry / high-UV
Southwest, high desert
Intense UV greys and checks cedar quickly; owners either accept the silver patina or budget for a penetrating oil finish on a tight recoat cycle.
Regional Examples:
Historic districts
New England, Mid-Atlantic
Preservation boards often mandate a specific exposure, grade, or coursing style to match the original — sometimes double-course "shadow" walls.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
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Don't guess at the container size — overage fees run $100–$300+ when you hit the weight cap or fill past the line. See the right size for this material.
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How to Use This Calculator
- Enter each wall: width, height, and gable rise for triangular gable ends.
- Add the total window and door area to deduct, in square feet.
- Pick the product (16"/18"/24" sawn shingle or handsplit shake) and grade (#1 Blue or #2 Red Label).
- Choose single or double course and set the weather exposure — leave it blank to use the CSSB maximum.
- Enter total corner length, pick a complexity/waste level, and calculate for bundles, squares, coursing, and fasteners.
Exposure, Grade & Waste
Coverage per bundle scales linearly with exposure, so a wider exposure buys fewer bundles — but the calculator caps exposure at the CSSB maximum for your product and grade (#2 Red Label carries ~15% less than #1 Blue). Waste runs 10% on simple walls up to ~18% on gable-heavy or staggered-course work. Cedar must be fastened with hot-dipped galvanized (ASTM A153) or stainless nails only.
Frequently Asked Questions
How many bundles of cedar shingles do I need per square?
For #1 Blue Label sawn shingles, 4 bundles cover one square (100 sq ft) of wall at the reference exposure — 5-1/2 inches for 18-inch Perfection shingles. Handsplit and resawn shakes are thicker, so 5 bundles make a square. But that's only at the reference exposure: because a bundle holds a fixed total shingle width, coverage per bundle scales linearly with exposure. Widen the exposure and each bundle covers more wall, so you buy fewer bundles for the same area.
How does weather exposure change the coverage?
Coverage per bundle = (100 ÷ bundles-per-square) × (your exposure ÷ the reference exposure). So an 18-inch #1 shingle covers about 25 sq ft per bundle at a 5-1/2 inch single-course exposure, but roughly 64 sq ft per bundle at a 14-inch double-course exposure (25 × 14 ÷ 5.5). This is why cedar sidewall estimating starts from exposure, not board count. The calculator caps your exposure at the CSSB maximum for the product and grade so you can't under-order by over-exposing.
What is double coursing and how does it change materials?
Double coursing lays two layers per course — a cheap undercoursing shingle hidden beneath an exposed #1 outer shingle — which allows a much wider weather exposure (up to ~14 inches for 18-inch shingles) and a deep shadow line. It roughly doubles your bundle order: you need an equal count of low-grade (#3 / undercoursing) bundles in addition to the #1 outer-course bundles. Select 'Double course' and the calculator adds the undercourse bundles automatically.
What's the difference between #1 Blue Label and #2 Red Label?
CSSB Certi-label #1 Blue Label is the premium grade — 100% clear, 100% heartwood, 100% edge grain — and carries the full maximum exposure. #2 Red Label permits some flat grain and limited sapwood and carries roughly 15% less maximum exposure, so it needs a tighter exposure (and slightly more material) for the same weather-tightness. The calculator reduces the exposure cap and adds a few points of waste when you pick #2.
What nails should I use for cedar shakes and shingles?
Only corrosion-resistant fasteners: hot-dipped galvanized (ASTM A153) or Type 304/316 stainless steel, ring-shank preferred. Cedar's natural extractives corrode ordinary steel, and electro-galvanized or bright nails bleed black streaks through the shingles within a season. Use two nails per shingle, about 3/4 inch in from each edge and 1 inch above the butt line of the next course, so the heads stay concealed. Plan on roughly 2 pounds of nails per square of single-course wall.
Does this work for polymer cedar-look shake panels?
No — use the vinyl siding calculator for those. Products like CertainTeed Cedar Impressions are molded polymer panels that lock together like vinyl and are estimated by panel and box, not by exposure against a bundle. This calculator is for natural Western Red Cedar sawn shingles and handsplit shakes graded to the CSSB Certi-label system, which is a completely different take-off.
How much waste should I add for cedar sidewall?
The CSSB/JLC baseline is 10% on simple, straight walls. Add more for cut-up work: 14% for some gables and openings, and 15–20% for many gables, dormers, or deliberately staggered random-width courses. Cedar waste is real because you're cutting many small individual units and trimming at every corner and opening. Corners get their own allowance — about one extra square per 100 linear feet of inside and outside corners.