Wood Shingles and Shakes

Wood Shingles and Shakes

Wood shingles and shakes are steep-slope roof coverings cut or split from naturally durable softwoods, most often western red cedar but also Alaska yellow cedar, redwood, cypress, eastern white pine and preservative-treated southern pine. A shingle is sawn on both faces to a uniform taper and lies flat; a shake is split from the log on at least one face, is thicker and more irregular, and produces a heavily textured roof. The distinction is relatively recent: historically all such units were called shingles, and the term "shake" came into use to separate the split products from sawn ones. Wood roofing is governed by IRC Sections R905.7 (shingles) and R905.8 (shakes) and their IBC equivalents, 1507.8 and 1507.9, and by the grading rules of the Cedar Shake & Shingle Bureau (CSSB). This article covers the material class broadly; for a detailed treatment of western red cedar products, grades and Certi-label branding see Cedar Roofing.

Species and wood quality

Only the heartwood of decay-resistant species is suitable for roofing. The National Park Service notes that western red cedar, eastern white pine and white oak are the most readily available today, with cypress and red oak obtainable on custom order and species such as yellow pine and hemlock used only when preservative-treated. The oils and extractives in cedar and redwood heartwood are what resist moisture and fungi; sapwood has none of this protection and is limited or excluded by grading rules.

Grain orientation is as important as species. Edge-grain (vertical-grain) units, in which the growth rings run perpendicular to the face, shrink and swell less and resist cupping and curling; flat-grain units are more prone to curl. CSSB Premium Grade shakes are 100 percent edge grain and clear heartwood, while Number 1 Grade permits up to 20 percent flat grain per bundle; the only difference between the two grades is flat-grain content. In British Columbia, the RCABC standard goes further and accepts only 100 percent edge-grain shakes with no flat grain.

Shingles versus shakes

Attribute	Wood shingles	Wood shakes
Manufacture	Sawn both faces; smooth, uniform taper	Split on at least one face (handsplit-resawn, tapersplit, straightsplit) or taper-sawn with a textured look
Common lengths	16, 18 and 24 in.	18 and 24 in.
Butt thickness	Thin (measured as bundles per inch)	1/2 in. (medium) or 3/4 in. (heavy); 3/8 in. available in 24-in. handsplit
Minimum slope (IRC)	3:12	4:12
Grades permitted by code	CSSB Grades 1, 2 or 3	Grade 1 (taper-sawn shakes Grade 1 or 2)
Interlayment	Not required	Felt interlayment between courses required
Appearance	Trim, refined, historic New England and Colonial styles	Rustic, deep shadow lines

Service life

Longevity depends on grade, grain, climate, slope, exposure, ventilation, shade and maintenance more than on the nominal product. The CSSB puts the average life of a cedar roof at approximately 30 to 40 years and notes that pressure-treated preservative products generally last longer, especially in humid areas. The National Park Service reports a wider historical range, 15 to over 60 years, observing that straight edge-grain heartwood shingles have been known to last more than sixty years while 15 to 30 years is a more realistic expectation for most premium modern wooden shingle roofs. Roofs that dry quickly after rain, because they are steep, unshaded, laid on spaced sheathing or a ventilated underlayment, and kept clear of debris, sit at the top of these ranges; shaded, mossy, low-slope roofs sit at the bottom. Compare How Long Does a Roof Last.

Fire performance and wildfire regions

Untreated wood is combustible, and this is the material's most serious limitation. Fire performance is expressed as a Class A, B or C roof assembly. According to the CSSB, both Class C and Class B pressure-impregnated fire-retardant treatments are available, and a Class B-treated product installed in a special assembly (typically over a fire-resistant cap sheet or gypsum layer) creates a Class A roof system; the treatment is marketed under the Certi-Guard label. No untreated wood shingle or shake achieves a fire classification.

Wildfire authorities are direct about the risk. FireSmart BC advises that Class A-, B- or C-rated roofing such as metal, asphalt, clay and composite tile is preferred, and that untreated wood shakes "create a dangerous combination of combustible material and crevices for embers or firebrands to enter." Some municipalities in wildland-urban interface zones in Canada and the United States restrict or prohibit untreated wood roofs, and insurers may surcharge them. Anyone considering a wood roof in the interior of British Columbia, Alberta's foothills, or the western U.S. should confirm local rules first; see Roofing Building Codes and Permits.

Installation

Deck and sheathing. Both shingles and shakes may be laid over solid or spaced sheathing; spaced sheathing uses 1×4 boards set on centres equal to the weather exposure so that fasteners land on wood. Model codes require solid sheathing where the average January temperature is 25°F (−4°C) or lower, or wherever ice can form at the eaves, which covers most of Canada and the northern United States. The CSSB adds that solid sheathing is used in areas with wind-driven snow and may be required under treated products, and that plywood is the only solid sheet sheathing tested with shakes and shingles.

Slope and exposure. Shingles require a slope of at least 3:12 and shakes at least 4:12. Exposure, the portion of each course left to the weather, is reduced on lower slopes so that the roof remains at least three layers thick. RCABC's British Columbia standard, for example, gives standard exposures on 4:12 and steeper of 5 in. for 16-in. shingles, 5-1/2 in. for 18-in. shingles and 7-1/2 in. for 24-in. shingles, with reduced exposures down to a 3:12 minimum, and a two-ply shake roof exposure of no more than 7-1/2 in. for 18-in. shakes and 10 in. for 24-in. shakes. Code caps the exposure of 24-in. by 3/8-in. handsplit shakes at 7-1/2 in.

Interlayment and underlayment. Shakes are laid with a strip of felt between courses (interlayment) that complies with ASTM D226 Type I. The CSSB recommends an 18-in. wide strip of No. 30 felt over the top portion of each course, positioned so its bottom edge sits above the butt at twice the weather exposure; the felt acts as a baffle against wind-driven snow and forces water back to the surface. In cold regions an ice barrier at the eaves is required; RCABC specifies self-adhesive rubberized asphalt (or equivalent) from the roof edge to at least 36 in. up the slope and past the interior wall line. See Roof Underlayment Guide.

Fastening and spacing. Each unit is fixed with two corrosion-resistant fasteners penetrating at least 3/4 in. into the sheathing; shingles are spaced 1/4 to 3/8 in. apart with side laps of at least 1-1/2 in., while shakes of naturally durable wood are spaced 3/8 to 5/8 in. Stainless steel (Type 304, or 316 near salt water) or hot-dip galvanized nails are used; RCABC notes that only stainless or hot-dip zinc-coated nails are acceptable with preservative- or fire-retardant-treated products, because the treatment chemistry attacks lesser coatings.

Ventilation. Wood roofing lasts longest when it can dry from both faces. Historic roofs achieved this with spaced sheathing or by laying long shingles on sleepers to create air channels beneath; a cedar roof at Old Fort Niagara built this way lasted more than 60 years in a harsh, moist environment. Where shingles are installed over spaced sheathing with the underside open to the attic, the attic must be ventilated to code, and the shingles must not be backed with material that fills the air gap. On solid decks, a ventilating synthetic mat under the shingles serves the same purpose. See Roof Ventilation.

Weight and insulation

Wood roofing is light, generally lighter than asphalt shingles and far lighter than tile or slate, so it rarely requires structural upgrades and is a practical replacement for other light coverings on older homes. Wood is a modest insulator and a cedar roof with felt interlayment adds a small amount of thermal resistance, but it should not be counted toward code-required attic insulation; that comes from the attic assembly. See Roof Insulation.

Maintenance

• Keep the surface free of leaves, needles and moss; debris holds moisture and, in wildfire regions, provides fuel for embers.
• Trim overhanging branches to improve sun and airflow.
• Inspect annually for split, cupped or missing units, exposed or rusting fasteners and worn flashings; individual pieces are readily replaced.
• Use low-pressure washing only; high-pressure washing erodes the softer earlywood and shortens life.
• Preservative and water-repellent treatments can extend service life; CSSB notes that Certi-Last pressure-treated products resist moss and mildew, while surface treatments should follow the treater's or manufacturer's guidance so that fire-retardant warranties are not voided.

Environmental considerations

Wood is renewable and biodegradable, and cedar shakes and shingles are often produced from salvage and second-growth timber; some producers offer FSC-certified stock that can contribute to LEED Certification material credits. Old wood roofing can be chipped or composted unless it has been treated, in which case it should be disposed of per local rules. Against these benefits are shorter service life than slate, tile or metal and, where fire treatment is required, the chemistry of the treatment.

Comparison with alternatives

• Asphalt Shingles – Lower cost, Class A fire rating in standard assemblies, minimal maintenance, but a manufactured look.
• Metal Roofing – Non-combustible, long-lived, sheds snow well; can be profiled to mimic shakes.
• Slate Roofing and Clay and Concrete Tiles – Non-combustible and very long-lived but heavy and costly.
• Synthetic (polymer) shakes – Lightweight, Class A available, imitate split cedar with less maintenance.

Frequently Asked Questions

What is the difference between a wood shingle and a shake?

A shingle is sawn smooth on both faces to a uniform taper and lies flat; a shake is split from the block on at least one face (or taper-sawn with a rough texture), is thicker, and gives a rustic, heavily shadowed roof. Codes treat them differently: shingles may go on 3:12 slopes, shakes need 4:12 and a felt interlayment between courses.

How long does a wood shake or shingle roof last?

The Cedar Shake & Shingle Bureau cites an average of about 30 to 40 years. The National Park Service reports 15 to over 60 years, with edge-grain heartwood roofs exceeding 60 years but 15 to 30 years being realistic for many modern roofs. Steep slope, good ventilation, sun exposure and regular cleaning push a roof toward the upper end.

Can a wood roof be fire-rated?

Only with pressure-impregnated fire-retardant treatment. Treated products (Certi-Guard) achieve Class C or Class B on their own, and a Class B product installed in a special assembly produces a Class A roof system. Untreated wood has no fire classification, and FireSmart BC warns that untreated shakes trap embers; check local wildfire-zone rules before specifying.

Which wood species are used for roofing?

Western red cedar dominates, with Alaska yellow cedar, redwood, cypress and eastern white pine also used; white oak and red oak appear on historic restorations, and southern pine is acceptable when preservative-treated. Only decay-resistant heartwood should be used, and edge-grain units resist curling far better than flat-grain ones.

Do wood roofs need solid sheathing in Canada?

Usually yes. Model codes require solid sheathing wherever the average January temperature is 25°F (−4°C) or lower or where eave ice can form, which covers most of Canada, and the CSSB recommends solid (plywood) sheathing where wind-driven snow occurs. An eave ice barrier and stainless or hot-dip galvanized nails are also standard in northern practice.

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Related Resources

• Cedar Roofing
• Wood Shingles
• Wood Shakes
• Roofing Materials
• Asphalt Shingles
• Tile Roofing
• Clay and Concrete Tiles
• Metal Roofing
• Slate Roofing
• Roof Structure
• Roof Pitch
• Roof Ventilation
• Roof Underlayment Guide
• Roof Insulation
• Roofing Building Codes and Permits
• How Long Does a Roof Last
• Roof Inspection and Maintenance
• Residential Roofing
• Commercial Roofing
• LEED Certification
• Roof Repair vs Replacement