A cedar shake or wood shingle roof is installed on solid or spaced sheathing over a slope of at least 3:12, with exposure, side lap, spacing and fasteners set by 2021 International Residential Code (IRC) Sections R905.7 (shingles) and R905.8 (shakes). Each piece takes two corrosion-resistant fasteners that penetrate the sheathing at least 3/4 inch.
A wood shingle is a thin, sawn, tapered piece of naturally durable wood. A wood shake is a thicker piece that is split or sawn. The adopted code edition and local amendments govern, and the manufacturer's instructions apply on top of the code.
Key facts
- Wood shingles and shakes may be installed on solid or spaced sheathing, and spaced boards must be at least 1-inch by 4-inch nominal (2021 IRC Sections R905.7.1 and R905.8.1).
- Wood shingles and wood shakes are used only on slopes of 3:12 (25-percent slope) or greater (2021 IRC Sections R905.7.2 and R905.8.2).
- Each shingle or shake gets two fasteners, with at least 3/4 inch of penetration into the sheathing (2021 IRC Sections R905.7.5 and R905.8.6).
- Side lap between joints in adjacent courses must be at least 1-1/2 inches (2021 IRC Sections R905.7.5 and R905.8.6).
- The starter course for shakes is doubled at the eaves (2021 IRC Section R905.8.7).
- Valley flashing is No. 26 gage corrosion-resistant sheet metal, with an end lap of at least 4 inches (2021 IRC Sections R905.7.6 and R905.8.8).
What is the difference between wood shingles and wood shakes?
Shingles are sawn and thin, while shakes are thicker and split or sawn, and the IRC gives each its own spacing, exposure, nail and underlayment rules.
2021 IRC Sections R905.7 and R905.8: wood shingles compared with wood shakes.
| Item | Wood shingles (R905.7) | Wood shakes (R905.8) |
|---|---|---|
| Minimum slope | 3:12 | 3:12 |
| Minimum grade | 1, 2 or 3 (Table R905.7.4) | Grade 1 or 1 and 2 by type (Table R905.8.5) |
| Spacing between pieces in a course | 1/4 inch to 3/8 inch | 3/8 inch to 5/8 inch |
| Side lap | Not less than 1-1/2 inches, and no two joints in direct alignment in any three adjacent courses | Not less than 1-1/2 inches in adjacent courses |
| Interlayment | None required by Section R905.7 | 18-inch-wide strips of not less than No. 30 felt between courses (R905.8.4, R905.8.7) |
| Valley flashing | 10 inches each way from centerline below 12:12, 7 inches at 12:12 and steeper | Not less than 11 inches each way |
| Exposure table | Table R905.7.5(1) | Table R905.8.6 |
Each bundle must carry a label from an approved grading or inspection bureau (Sections R905.7.7 and R905.8.9).
What deck does a cedar shake roof need?
A wood shake or shingle roof goes on solid sheathing or on spaced sheathing, and solid sheathing is mandatory in cold climates where an ice barrier is required.
Spaced sheathing means boards, not panels, with gaps between them. Under Sections R905.7.1 and R905.8.1, the boards must be at least 1-inch by 4-inch nominal and spaced on centers equal to the weather exposure, so each row of fasteners lands on a board. For shakes, where 1-inch by 4-inch boards are at 10 inches on center, extra 1-inch by 4-inch boards go between them.
Sections R905.7.1.1 and R905.8.1.1 require solid sheathing on the part of the roof that needs an ice barrier where the average daily temperature in January is 25°F (-4°C) or less. See ice and water shield for the barrier extent and roof sheathing thickness for panel thickness.
How are spaced sheathing boards nailed to the rafters?
Boards are face nailed to each bearing under 2021 IRC Table R602.3(1), items 20 (1 by 6) and 21 (1 by 8 and wider). Take the nail count and type from the printed table for your board width.
What is the minimum slope for a wood shingle or shake roof?
The minimum slope is 3 units vertical in 12 units horizontal (25-percent slope) for both wood shingles and wood shakes (Sections R905.7.2 and R905.8.2).
Table R905.7.5(1) has two slope columns for shingles, 3:12 to less than 4:12 and 4:12 or steeper. Table R905.8.6 lists shakes only at 4:12 or steeper, so it gives no shake exposure for 3:12 to 4:12. On such a roof, get the manufacturer's instructions and confirm with the building department. For how pitch is written and drawn, see roof pitch and slope.
What underlayment and interlayment go under wood shakes?
Underlayment must meet Section R905.1.1, an ice barrier goes in where Section R905.1.2 requires one, and shakes also need interlayment between courses.
Table R905.1.1(2) points wood shingles and wood shakes to the manufacturer's installation instructions for part of the slope range, so read that table and the product literature together. Interlayment must be ASTM D226 Type I (Section R905.8.4). Section R905.8.7 places each felt strip so its lower edge sits above the butt end of the shake it covers by twice the weather exposure, keeping the felt out of the weather.
What is the maximum exposure for cedar shingles?
Exposure is the part of each shingle left uncovered, and Table R905.7.5(1) sets the maximum by length, grade and slope.
2021 IRC Table R905.7.5(1): wood shingle weather exposure (inches), shingles of naturally durable wood.
| Length (inches) | Grade | 3:12 to under 4:12 | 4:12 or steeper |
|---|---|---|---|
| 16 | No. 1 | 3-3/4 | 5 |
| 16 | No. 2 | 3-1/2 | 4 |
| 16 | No. 3 | 3 | 3-1/2 |
| 18 | No. 1 | 4-1/4 | 5-1/2 |
| 18 | No. 2 | 4 | 4-1/2 |
| 18 | No. 3 | 3-1/2 | 4 |
| 24 | No. 1 | 5-3/4 | 7-1/2 |
| 24 | No. 2 | 5-1/2 | 6-1/2 |
| 24 | No. 3 | 5 | 5-1/2 |
These are maximums, and the manufacturer's instructions can be tighter.
What is the maximum exposure for wood shakes?
Table R905.8.6 caps shake exposure by product, length and grade, for slopes of 4:12 or steeper only.
2021 IRC Table R905.8.6: wood shake weather exposure (inches), 4:12 pitch or steeper.
| Product | Length (inches) | Grade | Exposure |
|---|---|---|---|
| Shakes of naturally durable wood | 18 | No. 1 | 7-1/2 |
| Shakes of naturally durable wood | 24 | No. 1 | 10 (footnote a) |
| Preservative-treated tapersawn Southern Yellow Pine | 18 | No. 1 | 7-1/2 |
| Preservative-treated tapersawn Southern Yellow Pine | 24 | No. 1 | 10 |
| Preservative-treated tapersawn Southern Yellow Pine | 18 | No. 2 | 5-1/2 |
| Preservative-treated tapersawn Southern Yellow Pine | 24 | No. 2 | 7-1/2 |
| Taper-sawn shakes of naturally durable wood | 18 | No. 1 | 7-1/2 |
| Taper-sawn shakes of naturally durable wood | 24 | No. 1 | 10 |
| Taper-sawn shakes of naturally durable wood | 18 | No. 2 | 5-1/2 |
| Taper-sawn shakes of naturally durable wood | 24 | No. 2 | 7-1/2 |
Footnote a: for 24-inch by 3/8-inch handsplit shakes, the maximum exposure is 7-1/2 inches. Table R905.8.5 sets the minimum grade for each shake type, with grading rules from the Cedar Shake and Shingle Bureau or, for Southern pine, the Forest Products Laboratory of the Texas Forest Services.
What nails and fasteners are used on wood shingles and shakes?
Untreated shingles and shakes take box nails sized by Table R905.7.5(2), made of Type 304 or 316 stainless steel or hot-dipped galvanized steel.
2021 IRC Table R905.7.5(2): nail requirements for wood shakes and wood shingles.
| Product | Nail type, minimum length and shank diameter (inches) |
|---|---|
| 18-inch straight-split shakes | 5d box, 1-3/4 by 0.080 |
| 18-inch and 24-inch handsplit and resawn shakes | 6d box, 2 by 0.099 |
| 24-inch taper-split shakes | 5d box, 1-3/4 by 0.080 |
| 18-inch and 24-inch tapersawn shakes | 6d box, 2 by 0.099 |
| 16-inch and 18-inch shingles | 3d box, 1-1/4 by 0.076 |
| 24-inch shingles | 4d box, 1-1/2 by 0.076 |
The rest of the fastener rules in Sections R905.7.5 and R905.8.6:
- Hot-dipped galvanized nails need a coating weight of ASTM A153 Class D (1.0 oz/ft2).
- Two 16-gage Type 304 or 316 stainless staples, crown 7/16 inch minimum to 3/4 inch maximum, may replace nails.
- Within 15 miles of saltwater, and for fire-retardant or preservative-treated pieces, use Type 316 stainless steel.
- Where the sheathing is thinner than 3/4 inch, the fastener goes through it.
How is the starter course laid and where do valleys go?
At the eaves, the starter course for shakes is doubled, and the bottom layer is 15-inch, 18-inch or 24-inch shakes or wood shingles (Section R905.8.7). Fifteen-inch or 18-inch shakes may be used for the final course at the ridge. Section R905.7 has no starter course sentence, so follow the shingle manufacturer's instructions.
Valley flashing widths are in the comparison table above. The roof valley guide compares them with other coverings and covers the valley rafter.
What does a roof framing plan need to show for a wood shingle or shake roof?
The plan should state four things so the reviewer and roofer can check them against Chapter 9:
- Roof slope for every plane, with a note where any plane falls below 3:12 or, for shakes, below 4:12.
- Deck type: solid panels, or spaced boards at the exposure spacing, plus any zone that must be solid for the ice barrier.
- Covering and exposure: product, length, grade and the table used.
- Valley and eave details as notes, including the doubled shake starter course.
Rafters are sized separately from the rafter span chart tables. The roof framing plan guide shows where these notes belong.
Summary
Wood shingles and shakes under the 2021 IRC need solid or spaced sheathing, a slope of at least 3:12, two corrosion-resistant fasteners per piece with 3/4 inch of sheathing penetration, and a side lap of at least 1-1/2 inches. Exposure comes from Table R905.7.5(1) for shingles and Table R905.8.6 for shakes, and shakes also need a doubled starter course and interlayment. Local amendments and the manufacturer's instructions govern.
Framing Plan is a preliminary drawing aid. It draws joist layouts, beams and openings and exports PNG, PDF and DXF, but it does not check code or size members, and its editor works in millimeters. Open the framing studio to sketch the framing, then add the slope, deck and roofing notes by hand for your reviewer.