Metal, tile & flat
Cedar shakes and shingles: exposure, bundles and lifespan
A bundle of cedar does not cover a fixed area: it covers more at a longer exposure. The Bureau's rule makes the count simple once that is clear.
Shakes and shingles are different products
Both are made from western red cedar (and some from eastern white cedar), and both come in 16, 18 and 24 inch lengths. Shingles are sawn on both faces into a smooth, tapered piece and laid much like asphalt shingles, without anything between courses. Shakes are split on at least one face (handsplit, or tapersawn on the back), thicker and rougher, and laid with an 18-inch strip of felt interlayment woven between each course to shed wind-driven rain past the gaps that a rough split leaves.
The Cedar Shake and Shingle Bureau (CSSB) grades both and publishes the coverage and exposure tables that roofers use.
Exposure sets coverage
The exposure is how much of each piece shows to the weather. The rest is covered by the courses above. A longer exposure means fewer layers over each point and fewer pieces per square; a shorter one means more layers, more pieces and a thicker roof.
The Bureau’s tables come down to one rule: at its reference exposure a product covers a square with four bundles (shingles) or five bundles (shakes), and coverage scales in proportion to exposure.
| Product | Reference exposure (4/12 and steeper) | Bundles per square there | Shorter exposure example |
|---|---|---|---|
| 16 in shingles | 5 in | 4 | 3¾ in on 3/12–4/12: 5.3 |
| 18 in shingles | 5½ in | 4 | 4¼ in on 3/12–4/12: 5.2 |
| 24 in shingles | 7½ in | 4 | 5¾ in on 3/12–4/12: 5.2 |
| 18 in shakes | 7½ in | 5 | 5½ in: 6.8 |
| 24 in shakes | 10 in | 5 | 7½ in: 6.7 |
Exposures longer than the reference are not allowed: there would be too few layers. Shorter exposures are required on shallower pitches and sometimes chosen for a heavier look.
Shakes and shingles on two roofs
2,000 square feet of 24-inch shakes at a 10-inch exposure, 80 feet of eaves, 40 feet of ridge, 10% waste:
- Coverage: 20 sq ft per bundle, 5 per square
- Field: 2,000 × 1.10 ÷ 20 = 110 bundles; doubled eave course: 3.3 bundles
- Total: 114 bundles, plus 3 bundles of hip and ridge
1,600 square feet of 18-inch shingles at 5½ inches:
- Coverage: 25 sq ft per bundle, 4 per square; field 70.4; eave course 1.1
- Total: 72 bundles, plus 2 of hip and ridge
From the cedar shake calculator.
Pitch
Cedar shingles need about 3/12 or steeper, at the reduced exposures for 3/12 to 4/12; shakes about 4/12. On shallower roofs cedar is not a weatherproof roof. The pitch calculator tells you where a roof sits, and the roof area calculator gives the area the bundles cover.
Installation that makes cedar last
Cedar fails from the inside when it cannot dry. The details that keep it dry:
- Air underneath. Spaced sheathing (1×4 or 1×6 boards with gaps) or a ventilated mat over solid sheathing, so the pieces dry from both faces.
- Gaps between pieces. ¼ to ⅜ inch for shingles, ⅜ to ⅝ for shakes, so wet wood can swell, with joints offset at least 1½ inches from the course below.
- Stainless steel nails, two per piece, about ¾ inch above the exposure line of the next course; type 316 near salt water. Galvanized nails stain and corrode.
- Interlayment between every course of shakes.
- A doubled first course at the eave (tripled for some shake installations), which the calculator adds.
Life and maintenance
Industry life-expectancy surveys put cedar shakes at about 25 to 30 years and shingles a little less. Climate makes the biggest difference: dry, sunny regions are easy on cedar, damp, shaded and humid ones hard, with moss and rot. Keeping the roof clear of debris, trimming overhanging branches and periodic treatment extend it; neglect shortens it.
| Cedar shakes | Architectural asphalt | |
|---|---|---|
| Installed cost per square (2025 surveys) | $700 to $1,400 | $450 to $800 |
| Expected life | 25 to 30 years | 25 to 30 years |
| Weight per square | 300 to 400 lb | 250 to 350 lb |
| Maintenance | cleaning, treatment | little |
On cost per year cedar is usually the dearer roof; people choose it for its look and its weight, light enough for most structures, unlike tile and slate. The lifespan calculator does the comparison, how long roofs last sets cedar against the alternatives, and tile and slate covers the heavier traditional materials.
Fire
Untreated cedar burns, and some wildfire-prone jurisdictions restrict wood roofs or require fire-retardant-treated products with a Class A or B rating, sometimes over a special underlayment. Check the local code before choosing cedar, and buy the rated product if required.
Ordering
Order field bundles, hip and ridge units (factory-made in matching grades) and starter from the same supplier and grade. Like any natural product, colour varies between lots, and cedar weathers to grey in a year or two anyway. The waste allowance follows the roof shape as it does for asphalt; bundles per square and waste explains how to set it.