7.3 Wood Shingles & Shakes

Wood shingles and wood shakes remain legitimate steep-slope coverings where appearance, sustainability messaging, or historic match matter. Illinois exams expect clear differences between shingles and shakes, correct spacing and exposure, and awareness of fire-retardant treatments and moisture detailing. Wood fails early when installers treat it like asphalt.

Shingles Versus Shakes

Wood shingles are sawn on both faces to a relatively smooth, uniform taper. They lay flatter, produce a neater appearance, and typically use smaller exposures than shakes.

Wood shakes are traditionally split from the bolt, leaving a rough textured face; taper-sawn shakes blend sawn backs with thicker butts. Shakes are thicker at the butt, create deeper shadow lines, and generally need greater attention to underlayment interlacing or interlayment depending on the product and slope.

Do not use the words interchangeably on an exam. If a question says “shake,” answer with shake detailing; if it says “shingle,” use shingle exposure and spacing norms.

Species, Grades, and Durability

Western red cedar is the most common premium species for shingles and shakes in U.S. trade, valued for natural extractives that resist decay. Other species appear regionally. Grade marks indicate allowable defects and intended use (walls versus roofs). Roof grades must be suitable for weather exposure—wall grades on a roof are a defect.

Illinois summers can be humid; winters freeze wet wood. Choose material graded for roofing, store it off the ground and under cover, and avoid installing saturated bundles that will shrink dramatically after fastening.

Spacing, Exposure, and Fastening

Adjacent shingles or shakes in a course are spaced—commonly on the order of about 1/4 inch to 3/8 inch depending on product instructions and moisture content—so wood can expand when wet and so water can drain rather than sit in a tight joint. Joints are offset from course to course so water does not run in a continuous vertical seam.

Exposure is published by length and roof slope. Overexposing wood to stretch coverage is a classic failure mode: butts weather faster, headlap shrinks, and wind-driven rain enters. Underexposure wastes material but is safer than stretching.

Fasteners are typically corrosion-resistant nails placed in the concealed fastening zone so the next course covers the heads. Overdriving crushes fibers and invites water; underdriving leaves proud heads that hold the overlaying piece off the plane. Two fasteners per piece is standard unless the manufacturer specifies otherwise for wide units.

Spacing mindset

1. Leave side gaps for movement and drainage.
2. Offset joints between courses.
3. Keep exposures within product tables for the slope.
4. Cull warped, cracked, or excessively knotty pieces.
5. Maintain straight lines—wood roofs telegraph wavy chalk lines forever.

Underlayment and Interlayment

Solid sheathing with appropriate underlayment is common. Some shake systems historically used skip sheathing for drying; modern practice and local Illinois codes often prefer solid decks with approved underlayments—follow the product instructions and the authority having jurisdiction.

In ice-dam regions, eave membranes protect the deck when meltwater backs up under wood courses. Valleys need metal designed for wood thickness and debris. Because wood is organic, trapping moisture against the butts with impermeable details that never dry can accelerate decay—balance ice protection with the manufacturer’s drying strategy.

Fire-Retardant Treatments

Untreated wood roofing has limited fire performance. Pressure-impregnated fire-retardant treatments and listed assemblies can improve fire classification for jurisdictions that restrict untreated wood roofs. Treatment must be compatible with roofing use; field-applied coatings are not automatically equal to pressure treatments or listed systems.

Illinois municipalities differ. Some historic districts allow wood for authenticity; others restrict it near dense housing. Exam takeaway: know that fire treatment and listing status can determine whether wood is allowed, and treated products must still be installed to the listing (fasteners, underlayment, and slope).

Snow, Ice, and Maintenance

Wood roofs hold snow differently than slick metal or tile. Ice dams still form with poor attic insulation and ventilation. After storms, remove debris that keeps butts wet. Moss and algae retain moisture—address gently without destroying the wood surface. Expect periodic replacement of weathered courses on the most exposed elevations.

Foot traffic crushes fibers; use walk boards. Flashing repairs should use compatible metals that do not bleed staining onto cedar.

Moisture Cycle Specific to Illinois

Spring thaw followed by humid summer weather keeps wood near fiber saturation longer than arid climates do. That cycle rewards correct spacing, sound underlayment at eaves, and prompt repair of flashing leaks that soak starter courses. Avoid burying wood roofs under thick non-breathable coatings that trap moisture. When estimating remaining life, inspect the butt edges and the underside at eaves—decay often starts where ice and drip edges keep fibers wet.

Professional Judgment

Wood shingles and shakes succeed when the installer respects product identity (shingle vs shake), spacing, exposure, fasteners, underlayment, and fire rules. They fail when joints are butted tight, exposures are stretched, untreated wood is used where banned, or ice protection is ignored. Those contrasts are exactly what Illinois steep-slope questions probe.