Mastering Roof Inspections: Wood Shakes and Shingles, Part 1

Manufacturing and Application Standards

Wood shakes and shingles are made primarily from western red cedar.  They are available in a variety of types and grades, and categorized according to their level of resistance to wind, impact and fire.

Standards for wood shake and shingle manufacturing and application are provided by a number of standard and code-producing organizations, including:

• ASTM International;
• Underwriters Laboratories (UL);
• the Cedar Shake and Shingle Bureau (CSSB);
• the International Residential Code (IRC);
• the Canadian Standards Association (CSA); and
• the National Fire Protection Association (NFPA).

Grading

Shakes and shingles must undergo and meet the following types of testing and performance standards.  However, you won’t be able to confirm visually that the wood roof you’re inspecting has qualified for any of these ratings unless documentation is provided.

Testing procedures are not specific to each roof-covering material. The different types of roof-covering materials all undergo the same tests.

• Wind

Shakes and shingles may be UL-certified to resist winds of up to 245 mph and 173 mph, respectively.

• Impact

Shakes and shingles are available in Class 3 and 4 impact ratings, with Class 4 being the most resistant to impact damage.

• Fire

Shakes and shingles are available in Class A, B or C fire rating, but you can’t just go out and buy a Class A-rated shingle or shake. Achieving a Class A rating requires that a Class B fire retardant-treated shake or shingle be installed above a heavy asphalt cap sheet. This is called a component system.  It requires more than one component to achieve the Class A fire rating.

Achieving the desired fire rating also requires adhering to the recommendations of the company that treated the shakes or shingles. These requirements may vary among treatment companies.  Failure to adhere to specific recommendations may void the warranty. You won’t be able to identify the fire rating of a shake or shingle just by looking at it. Again, documentation would have to be provided in order for you to provide confirmation of a sellers claim that a roof is rated Class A.

Preservative-Treated

CCA pressure-treated shakes and shingles are available that resist decay in humid climates. You won’t be able to tell by looking at them whether wood roofs have been treated with a fire-retardant or preservative.

Shake and Shingle Types  

Shakes are heavier, thicker and sometimes longer than wood shingles.

Shakes

Shakes come in four main types based on how they’re sawn or split. Sawn surfaces are smoother than split surfaces. The surface facing up is called the face, and the surface facing down is called the back.

Taper-split shakes have a split face and split back, and are tapered from butt to tip.

Straight-split shakes have a split face and split back, and are not tapered.

Hand-split shakes have a split face, a sawn back, and are tapered.

Taper-sawn shakes are sawn on both sides, similar to a shingle, but have a heavier butt, similar to a shake.

Medium and heavy shakes are available.  The medium is typically thinner than ¾-inch, and the heavy is thicker. Shakes are available in 18-inch and 24-inch lengths, and longer for applications at historical properties.

Shingles

Shingles are always tapered, always sawn, and are thinner than shakes. They’re available in 16-inch, 18-inch and 24-inch lengths.

Sidewall Shingles

Sidewall shingles are made for installation on exterior walls.  They may have one of many types of pre-finish or finish coatings different from the shingles used on roofs.

Shake and Shingle Grain Exposure

Shingles come in three basic grain exposures:  edge grain, flat grain and slash grain. The quality can be judged by the appearance of the grain.

Edge grain and flat grain are the most common types of shingles, although it’s not unusual to find some flat-grain shingles on a roof that has mostly edge grain.

• Edge Grain 

Edge-grain shakes and shingles have tight, straight grain and are the most stable.

Edge-grain shakes and shingles are cut perpendicular to the growth rings.

In edge-grain shingles, the grain is allowed to slant a maximum of 45° from vertical. Edge-grain shingles are the most stable over time and offer the greatest resistance.

Premium-grade shakes and shingles must be 100% edge grain.  Bundles of #1 shakes and shingles may include up to 20% flat-grain shingles.

• Flat Grain 

Flat-grain shakes and shingles have visible heartwood.

Flat-grain shakes and shingles are cut parallel to growth rings, with the grain oriented horizontally when viewed from the butt-end. The face of the shingles shows very wide grain with a fairly obvious centerline, as you can see here.

Because this type of shingle exposes the most sapwood to weather, it’s the least stable and most likely to check, split, erode and distort.

Flat-grain shakes and shingles are likely to split along the centerline during natural weathering.

• Slash Grain 

Slash-grain shakes and shingles have wavy grain.

Slash-grain shakes and shingles are also cut perpendicular to the growth rings but at an angle of more than 45° from vertical when viewed from the butt. Grain on the face of the shingle may appear wavy. Because the angle of the cut exposes more sapwood than edge-grain shingles do, slash-grain shingles are the least stable of the three types and are more prone to checking, splitting, erosion and distortion.