Wood Shake Roofing: Characteristics and Considerations
Wood shake roofing occupies a distinct position in the US residential roofing sector, valued for its natural insulation properties, dimensional depth, and historic aesthetic. This page covers the material classification, installation mechanics, common application scenarios, and the regulatory and decision factors that govern when wood shake is appropriate, restricted, or excluded as a roofing material. Contractors, property owners, and inspectors working with this roofing type encounter a specific set of code, fire rating, and maintenance obligations that differ materially from asphalt or metal alternatives.
Definition and scope
Wood shake roofing consists of hand-split or sawn wooden panels — typically Western red cedar, though Alaskan yellow cedar and pine are also used — installed in overlapping courses on a pitched roof deck. The term "shake" is formally distinguished from "shingle" in industry classification: shingles are sawn smooth on both faces, while shakes are split on at least one face, producing a rougher, more textured surface with greater thickness variation.
The Cedar Shake and Shingle Bureau (CSSB) maintains the primary North American grading standards for wood shake products. Under CSSB classification, shakes are graded as No. 1 (100% heartwood, 100% edge grain, clear face), with lower grades permitting increasing amounts of sapwood and flat grain. Thickness ranges from approximately 3/8 inch at the thin end to 3/4 inch or more at the butt for standard hand-split and resawn shakes.
Roofing shakes and shingles are addressed within the International Residential Code (IRC), specifically in Chapter 9, which covers roof assemblies and materials. Adoption and amendment of the IRC is jurisdiction-specific; contractors should verify whether the version in force in a given state or municipality includes local modifications.
Wood shake is categorized in the International Building Code (IBC) and relevant ASTM standards primarily by fire resistance. Untreated wood shake carries a Class C fire rating at best. Factory-applied fire retardant treatments can elevate products to Class A or Class B ratings, a distinction with direct permitting consequences in wildland-urban interface (WUI) zones and jurisdictions with heightened fire risk classifications.
How it works
Wood shake roofing functions through a drainage-by-slope system. Individual shake courses are laid with an exposed face (the "weather" portion) and an overlapping portion concealed by the course above. The headlap — the distance by which upper courses cover lower ones — determines both weather resistance and the required roof pitch.
A standard installation sequence follows this structure:
- Deck preparation — Structural sheathing (typically 1×6 spaced boards or solid OSB/plywood) is installed to code-required specifications; solid decking is required under most modern code versions for shake.
- Underlayment installation — An 18-inch-wide starter course of 30-pound felt or approved synthetic underlayment is applied at the eave; subsequent felt layers are interwoven between shake courses per CSSB installation guidelines.
- Starter course — A double layer of shakes is installed at the eave line to establish the proper exposure angle.
- Course installation — Each course is offset from the one below by a minimum 1.5-inch sidelap; fasteners are typically 2 stainless steel or hot-dipped galvanized nails per shake, driven no more than 3/4 inch from each edge.
- Ridge and hip finishing — Prefabricated shake ridge caps or field-fabricated units close the ridge assembly.
Ventilation is a functional requirement in wood shake systems. Unlike sealed membrane systems, wood shake is a "breathing" roof that relies on airflow to manage moisture. Inadequate attic ventilation — benchmarked under IRC Section R806 at a minimum net free ventilation area of 1/150 of the attic floor area — contributes directly to premature shake degradation, moss growth, and structural deck damage.
The natural service life of No. 1 cedar shakes on a properly maintained, adequately ventilated roof is 20 to 30 years in moderate climates, with shorter spans in high-humidity or freeze-thaw environments.
Common scenarios
Wood shake is most frequently encountered in the following contexts:
Historic and high-value residential properties — Properties in historic districts governed by local preservation ordinances or listed on the National Register of Historic Places may be required or strongly incentivized to maintain wood shake roofing for aesthetic continuity. The National Park Service Preservation Brief 45 addresses repair and replacement of historic wood shingle and shake roofs directly.
Pacific Northwest and mountain region construction — Western red cedar is regionally produced, making shake roofing cost-competitive in Oregon, Washington, and adjacent states. Contractor expertise and local supply chains are concentrated in these markets.
Wildland-Urban Interface (WUI) replacement projects — Properties in WUI zones subject to NFPA 1 (Fire Code) or California's Title 19 regulations may be required to replace untreated shake with Class A or Class B fire-rated alternatives or treated shake products. At least 35 states have adopted WUI-specific codes that restrict or condition wood shake use (International Code Council, WUI Code adoption tracking).
Insurance-driven replacement — Some property and casualty insurers have conditioned coverage or renewal on the removal of untreated wood shake roofing, particularly in fire-prone regions. This is a private contractual matter outside public regulatory frameworks, but it materially affects material selection at the project level.
Decision boundaries
The choice to install, retain, or replace wood shake roofing turns on a specific set of regulatory, structural, and environmental factors. Roofing professionals and property managers working through these decisions should reference the roofing listings directory to identify contractors with documented wood shake credentials in their jurisdiction.
Fire rating requirements are the primary binary decision gate. Jurisdictions classified as high fire hazard severity zones under state fire marshal designations, or subject to WUI overlay requirements, will restrict or prohibit unrated wood shake. Fire-rated shake products must carry third-party certification (typically from Underwriters Laboratories or equivalent) confirming Class A or Class B assembly performance.
Roof pitch is a structural boundary condition. Wood shake requires a minimum 3:12 pitch for standard installations; steeper pitches (4:12 and above) are standard for optimal drainage performance. Installations below minimum slope thresholds require special underlayment detailing and may not be code-compliant in jurisdictions enforcing current IRC editions.
Maintenance capacity is a practical threshold. Wood shake requires periodic cleaning, moss and algae treatment, and replacement of cracked or missing units on a cycle of approximately every 5 to 7 years. Structures without ongoing maintenance programs — rental portfolios, commercial properties, or owner-occupied homes in high-moisture zones — accumulate decay faster than the material's rated service life.
Comparison: treated vs. untreated shake
| Attribute | Untreated No. 1 Cedar Shake | Fire-Retardant-Treated Shake |
|---|---|---|
| Fire rating | Class C | Class A or Class B |
| WUI zone eligibility | Restricted or prohibited | Permitted where Class A/B required |
| Cost premium | Baseline | 15–40% above untreated (varies by treatment process and supplier) |
| Retreatment requirement | Not applicable | Some treatments require field retreatment after 10–15 years |
| Code citation | IRC Chapter 9 | IRC Chapter 9 + ASTM E84/E108 |
Permitting for wood shake roofing replacement typically follows the roofing permit process applicable in the local jurisdiction, which in most US municipalities requires a building permit for full replacements and may require a separate fire marshal review in WUI-designated areas. The scope of inspection — deck condition, underlayment, flashing, and ventilation — varies by jurisdiction but is standardized in jurisdictions enforcing the IRC.
Contractors performing wood shake work are subject to state contractor licensing requirements, which differ by state. For reference on how roofing service providers are structured and verified at the national level, see how to use this roofing resource.
References
- Cedar Shake and Shingle Bureau (CSSB) — Grading and Installation Standards
- International Residential Code (IRC) 2021, Chapter 9 — Roof Assemblies
- International Building Code (IBC) 2021
- National Park Service Preservation Brief 45 — Preserving Historic Wood Shingle and Shake Roofs
- NFPA 1 — Fire Code (National Fire Protection Association)
- Underwriters Laboratories (UL) — Roofing Material Certifications
- International Code Council — WUI Code Adoption Resources
- ASTM E108 — Standard Test Methods for Fire Tests of Roof Coverings