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CSA O118.1-08 (2018): Comprehensive Guide to Western Red Cedar Shingles and Shakes Standard
Understanding the Technical Requirements, Grading Rules, and Compliance for Cedar Roofing and Siding Products
CSA O118.1-08 (2018) is the authoritative Canadian standard for Western Red Cedar shingles and shakes. Originally published in 2008 and reaffirmed in 2018, this standard defines the material, dimensional, grading, and marking requirements for these premium wood roofing and siding products. It serves as the benchmark for manufacturers, specifiers, building officials, and installers across North America. This article provides a comprehensive technical overview of the standard, including its scope, key technical requirements, implementation guidance, and compliance considerations.
Scope and Application
The standard applies to shingles and shakes manufactured exclusively from Western Red Cedar (Thuja plicata) for use in roof coverings, wall cladding, and other architectural features. It covers both shingles (sawed on both sides) and shakes (split or sawn on one side, with a textured face). The document establishes:
- Acceptable wood species and quality
- Dimensional tolerances and grading designations
- Moisture content requirements
- Defect limits and permissible characteristics
- Marking, labeling, and certification requirements
CSA O118.1 is referenced by the National Building Code of Canada and many provincial codes, making compliance essential for construction projects requiring code acceptance.
Tip: When specifying cedar shingles or shakes for a project, always confirm that the product carries a certification mark accredited by the Standards Council of Canada (SCC) to CSA O118.1-08 (2018). This ensures the material meets the latest reaffirmed requirements.
Technical Requirements
Wood Species and Quality
Only heartwood of Thuja plicata is permitted. The standard requires that at least 90% of the bundle volume be heartwood (naturally resistant to decay). Sapwood is limited to a maximum of 10% and must be free of incipient decay. Specific defect restrictions include:
- Knots: limited by grade (tight knots allowed in lower grades)
- Checks and splits: controlled by length and location
- Wane, bark, and pitch pockets: prohibited in higher grades
- Machine damage: not permitted
Grading Designations
The standard defines distinct grades for shingles and shakes. The most common are summarized below.
| Product Type | Grade Name / Label | Description | Typical Application |
|---|---|---|---|
| Shingles | No. 1 (Blue Label) | Clear heartwood, tight knots ≤3/4″ allowed, edge grain preferred | Premium roofs, high-exposure walls |
| Shingles | No. 2 (Red Label) | Heartwood with some tight knots (≤1″), limited sapwood | Standard roofs, sidewalls |
| Shingles | No. 3 (Black Label) | Combination grades with larger knots, some sapwood and splits | Economy roofs, secondary structures |
| Shakes | Handsplit & Resawn | Split face, sawn back, heavy butt, textured surface | High-end roofs, rustic style |
| Shakes | Tapersplit | Split on both sides, tapered, smooth face | Medium-exposure roofs |
| Shakes | Straight-split | Split on both sides, uniform thickness, no taper | Walls, specialty roofs |
Dimensions and Tolerances
Shingles and shakes must comply with strict dimensional requirements. The table below gives nominal lengths and corresponding butt thicknesses for shingles.
| Length (inches) | Length (mm) | Minimum Butt Thickness (inches) | Minimum Width (inches) |
|---|---|---|---|
| 16 | 406 | 0.40 | 3 |
| 18 | 457 | 0.45 | 3 |
| 24 | 610 | 0.50 | 3 |
For shakes, butt thickness ranges from 0.25″ to 0.75″ depending on type and length. Lengths common for shakes are 18″ and 24″. Widths are random but must be within specified ranges. All products must have a moisture content not exceeding 15% at the time of packaging and shipment.
Physical and Mechanical Properties
While the standard primarily governs visual grading and dimensions, it also addresses durability. The high heartwood content ensures natural resistance to decay and insect attack. No chemical preservative treatment is required. The standard does not prescribe strength tests, but the grading rules inherently select for structural soundness. Products must be bundled and packaged to prevent damage during transport and storage.
Warning: Using non‑compliant cedar products can lead to premature failure, voided warranties, and non‑acceptance by building inspectors. Always request the supplier’s certification documentation traceable to CSA O118.1-08 (2018).
Implementation Highlights for Stakeholders
For Manufacturers
To claim compliance, manufacturers must implement a quality control program that includes regular monitoring of log quality, sawing patterns, drying, grading, and packaging. Third‑party inspection and certification by an accredited agency (e.g., CSA Group, Timber Products Inspection) are required to authorize use of the certification mark. The standard requires that each bundle be labeled with the grade, length, manufacturer identity, and certification mark.
For Specifiers and Architects
The selection of grade and product type should be based on exposure, climate, and aesthetic preference. Blue Label shingles are recommended for steep roofs and visible siding. For high‑wind or severe weather regions, ensure that fastening and exposure comply with the National Building Code and manufacturer instructions—the standard does not cover installation, but correct application is critical to performance.
For Installers
Handle bundles carefully to avoid breakage. Shingles and shakes should be acclimated to local conditions before installation. Follow the recommended exposure (weather exposure) for each grade/length combination. Use corrosion‑resistant fasteners (hot‑dipped galvanized or stainless steel) as specified by the code.
Success: Projects using certified CSA O118.1‑08 (2018) shingles and shakes consistently demonstrate long service life—often exceeding 30 years for roofs—when installed correctly. The heartwood’s natural extractives provide exceptional durability.
Compliance Notes and Certification
Compliance with CSA O118.1 is verified through a combination of manufacturer self‑inspection and independent third‑party audits. Key compliance aspects include:
- Certification mark: The product must bear a mark (e.g., CSA, TPI) that indicates conformity to the standard. The mark includes the standard number and reaffirmation year.
- Traceability: Manufacturers must maintain records of grading, production lots, and sales. Random audits ensure ongoing adherence.
- Non‑conforming product: Products failing to meet any requirement must be regraded or removed from the certified stream.
- Reaffirmation (2018): The 2018 reaffirmation confirmed that no technical changes were needed from the 2008 edition. The requirements remain current as of 2026.
Danger: Specifying or installing uncertified shakes can create liability issues. In Canada, building codes often require materials conforming to a referenced standard. Using uncertified products may result in stop‑work orders and costly replacement.
Frequently Asked Questions
Q: What is the difference between CSA O118.1 and CSA O118.2?
A: CSA O118.1 covers shingles and shakes for roofing and siding. CSA O118.2 covers Western Red Cedar bevel siding, shiplap, and tongue‑and‑groove patterns. Both are important standards for cedar products, but they address different product forms.
A: CSA O118.1 covers shingles and shakes for roofing and siding. CSA O118.2 covers Western Red Cedar bevel siding, shiplap, and tongue‑and‑groove patterns. Both are important standards for cedar products, but they address different product forms.
Q: Can I use No. 3 (Black Label) shingles for a primary roof?
A: No. 3 shingles are considered an economy grade and are not recommended for steep roofs or main structures due to larger knots and potential defects. They may be acceptable for gable ends, sheds, or low‑exposure walls. Check local code and manufacturer guidelines.
A: No. 3 shingles are considered an economy grade and are not recommended for steep roofs or main structures due to larger knots and potential defects. They may be acceptable for gable ends, sheds, or low‑exposure walls. Check local code and manufacturer guidelines.
Q: Does CSA O118.1 require pressure treatment for cedar shingles?
A: No. Western Red Cedar heartwood is naturally decay‑resistant. The standard does not mandate any chemical treatment. However, some building codes may require treatment in specific termite‑prone areas; always verify with the local authority having jurisdiction.
A: No. Western Red Cedar heartwood is naturally decay‑resistant. The standard does not mandate any chemical treatment. However, some building codes may require treatment in specific termite‑prone areas; always verify with the local authority having jurisdiction.
Q: How can I verify if a product is certified to CSA O118.1-08 (2018)?
A: Look for a certification mark on the bundle label. The mark should include the accreditation symbol of an SCC‑recognized agency, the standard number (CSA O118.1-08), and the grade designation. You can also request a certificate of compliance from the supplier or consult the certification body’s database.
A: Look for a certification mark on the bundle label. The mark should include the accreditation symbol of an SCC‑recognized agency, the standard number (CSA O118.1-08), and the grade designation. You can also request a certificate of compliance from the supplier or consult the certification body’s database.