Cedar Shake and Wood Shingle Roofing in Washington

Cedar shake and wood shingle roofing represents one of the most regionally significant roofing categories in Washington State, where the Pacific Northwest's forestry heritage, climate conditions, and historic building stock have all shaped its continued use. This page covers the classification of wood roofing products, their installation and performance characteristics, the regulatory and fire-rating framework governing their use in Washington, and the conditions under which wood roofing is appropriate or restricted. The distinction between cedar shakes and wood shingles carries both technical and code-compliance weight that affects permitting, insurance, and material selection across the state.

Definition and scope

Cedar shakes and wood shingles are two distinct product categories within the broader wood roofing classification. The difference is structural and code-relevant, not merely cosmetic.

Wood shingles are sawn on both faces, producing a smooth, uniform taper and a relatively flat profile. Cedar shakes are split on at least one face — hand-split shakes are split on both faces, while hand-split-and-resawn shakes are split on one face and sawn on the other. This split surface produces a rougher, more textured profile with greater thickness variation. Both products are graded under standards maintained by the Cedar Shake and Shingle Bureau (CSSB), which issues grading rules and quality marks recognized by building code authorities.

Grading classifications:

1. No. 1 (Blue Label / Handsplit) — 100% clear, edge-grain material; highest grade for roofing
2. No. 2 (Red Label / Handsplit) — allows flat grain and limited sapwood; suitable for secondary applications
3. No. 3 (Black Label) — utility grade; generally not specified for Washington roofing installations
4. Rebutted-Rejointed (R&R) — machine-trimmed for uniform sizing; used in some re-roofing applications

Western red cedar (Thuja plicata) is the predominant species used in Pacific Northwest production, with its natural extractive compounds providing baseline resistance to rot and insect damage. Pressure-treated and fire-retardant-treated (FRT) cedar products are separately classified and carry different code implications.

The scope of this page is limited to Washington State jurisdictions. Building codes, fire hazard zone designations, and local amendments vary by county and municipality; conditions in Oregon, Idaho, or British Columbia — despite geographic proximity — are not covered here.

How it works

Cedar roofing functions through a drainage-and-drying mechanism rather than a waterproof-barrier approach. Individual shakes or shingles are installed in overlapping courses across a roof deck, with each course offset from the one below. The overlap — governed by exposure width — sheds water by gravity while allowing air circulation between units.

Exposure width is the key installation variable. For No. 1 cedar shingles on a 4:12 pitch or steeper, standard exposure is 5 inches for 16-inch shingles, 5¾ inches for 18-inch shingles, and 7½ inches for 24-inch shingles, per CSSB installation guidelines. Reduced exposure is required on lower-slope applications.

The Washington State Energy Code (WSEC) and the Washington State Building Code (WSBC) adopt the International Building Code (IBC) and International Residential Code (IRC) with state amendments. Under IRC Section R905.7 (wood shingles) and R905.8 (wood shakes), specific substrate, underlayment, fastening, and flashing requirements apply. Washington-specific amendments address seismic and moisture exposure conditions not fully captured in the base IRC.

Underlayment requirements under Washington's climate conditions are addressed in detail at Roofing Underlayment in Washington. The high annual precipitation across western Washington — Seattle averages approximately 38 inches of rainfall per year (NOAA Climate Normals) — places particular importance on correct underlayment specification and deck ventilation.

Common scenarios

New residential construction on standard lots — Cedar shakes and shingles are permitted under the IRC as adopted by Washington, provided the installation meets fire classification requirements for the local jurisdiction. Class C is the minimum fire rating required in most residential zones; Class A or B may be required in Wildland-Urban Interface (WUI) areas.

Historic and craftsman-era home re-roofing — Washington has a substantial inventory of pre-1950 residential structures where cedar roofing is historically consistent. Historic Building Roofing in Washington addresses the additional considerations that apply when re-roofing structures subject to historic preservation review, including Washington State Historic Preservation Office (SHPO) oversight under RCW 27.34.

Wildland-Urban Interface (WUI) zones — A significant portion of Washington's residential geography falls within WUI designations administered at the county level and coordinated through the Washington State Department of Natural Resources (DNR). In WUI zones, untreated wood roofing is typically prohibited. Fire-retardant-treated (FRT) cedar products carrying a Class A rating from an accredited testing laboratory are required in these zones. Class ratings derive from ASTM E108 or UL 790 testing.

Re-roofing over existing cedar — Washington jurisdictions generally permit single-layer re-roofing where structural conditions allow, but multiple layers of wood shake create weight loading and moisture-trapping issues. Roof deck and sheathing condition — covered at Roof Deck and Sheathing in Washington — must be assessed before re-covering.

Moss and biological growth management — Western Washington's temperate, moist climate accelerates moss, lichen, and algae colonization on cedar surfaces. This is addressed specifically at Moss and Algae on Washington Roofs. Untreated biological growth accelerates moisture retention and fiber degradation, reducing service life.

Decision boundaries

The primary decision boundary in cedar roofing is fire classification vs. jurisdiction requirements. The regulatory context for Washington roofing maps the specific code adoption framework, but the operational rule is: untreated cedar in WUI zones is a code violation, not a preference issue. Local fire authority having jurisdiction (AHJ) determinations govern, and some jurisdictions have adopted amendments more restrictive than the base IRC.

Cedar shake vs. wood shingle — when each applies:

Cedar vs. alternative materials — Against asphalt shingle roofing in Washington, cedar carries higher installed cost and maintenance demand but a longer design lifespan when properly maintained — commonly cited in the 30-to-50-year range for No. 1 grade installations. Against metal roofing in Washington, cedar offers a traditional aesthetic but lower fire resistance in untreated form and greater biological growth susceptibility.

Permitting thresholds — Under Washington's statewide building code framework, roof replacement constitutes a regulated activity requiring a building permit in most jurisdictions. The local building department — not a roofing contractor — is the authority on whether a specific scope of cedar roofing work requires permit and inspection. Permitting concepts are further detailed at Permitting and Inspection Concepts for Washington Roofing.

Scope limitations: This page does not address commercial cedar roofing applications, roofing on tribal lands (which operate under separate federal and tribal jurisdictional frameworks), or the use of wood roofing in jurisdictions outside Washington State. Agricultural structures, temporary structures, and certain exempt accessory structures may fall outside the scope of the Washington State Building Code under RCW 19.27.170.

References

• Cedar Shake and Shingle Bureau (CSSB) — Grading and Installation Standards
• Washington State Building Code Council (SBCC)
• Washington State Building Code — RCW 19.27
• International Residential Code (IRC) — R905.7 and R905.8, ICC
• Washington State Department of Natural Resources — Wildland Fire and WUI
• Washington State Historic Preservation Office (SHPO) — RCW 27.34
• [NOAA Climate Normals — Seattle Precipitation Data](https://www.ncdc.noaa.gov