Wood Shakes
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Wood shakes might be considered the big brother to wood shingles. These provide a more rustic look than wood shingles. There are four types of wood shakes.
1. Straight-split or barn shakes. Straight-split shakes are split from the same end of a cedar block and do not have a taper. They are not usually used for house roofs. They have a uniform thickness of about 3/8 inch and come in 18-and 24-inch lengths.
2. Taper-split. Taper-split shakes are cut from alternate ends of a block so that the butt is at least 1/2 -inch thick. They are typically 24 inches long. These are not common since they are tough to make and are expensive.
3. Hand-split and re-sawn shakes are split the same as straight shakes except that they are thicker. A piece of wood that will be two shakes is split off a block. This block is then run through a saw on the diagonal producing two shakes with the back of each shake sawn smooth. The front of each shake is rough because it has been split.
4. Taper-sawn shakes are relatively new. They are sawn on both sides and may be thought of as an extra-thick wood shingle.
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Let’s look at some of the typical installation details.
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INSTALLATION DETAILS
Typical Size
Length 18 to 24 inches. Maximum width is 12 to 13 inches (some people recommend 8 inches as a maximum).
Typical Thickness
1/2 to 11/4 inches, measured at the butts.
Minimum Slope
4 in 12.
Exposure
71/2 inches for 18-inch long shakes and 10 inches for 24-inch shakes.
Head Lap
3 inches for 18-inch shakes and 4 inches for 24-inch shakes.
Fastener Type
Hot-dipped galvanized or stainless steel, aluminum or copper. Nails should be long enough to penetrate 3/4 inch into the sheathing, 13/4 - to 2-inch shakes are typical. Longer nails would be used on hips and ridges.
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Staples can be used. Stainless steel staples are recommended in wet climates and electroplate galvanized staples are satisfactory in drier climates. Pressure-treated shakes should have stainless steel fasteners.
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Number of Fasteners per Shake
2. Nails should be 3/4 inch from each side and 2 inches above the exposure line.
Can Vertical Joints in Alternating Courses Line Up?
No. On good installations they’ll line up only every four or five rows.
Overhang at Lower Edge
1 to 11/2 inches.
Overhang at Rake
1 to 11/2 inches.
Weight per Square of Roofing
220 to 450 pounds per square.
Underlayment Materials: None. On low-sloped roofs, #15 asphalt-saturated Interlay rather than underlay is often used. This typically consists of an 18- inch-wide strip of #30 felts that cover the top 4 inches of each shake and extend up onto the sheathing.
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Interlay
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The interlay is intended to stop wind-driven snow and rain from going up between the shakes. This is important on shakes because of the rough texture and considerable gaps that are created when one shake overlays another. You can think of the interlayment as a sock that is stuffed in the gap between adjacent shakes near the top of the underlying shake. Every shake should have interlayment as you move up the roof. This is more important on lower-sloped roofs.
There are exceptions. Some types of shakes (straight-split or taper-split) do not require interlay if you are in a snow-free area and the shake exposure is reduced to less than one third of the shake length. In this application, there will be three layers of shakes anywhere you cut through the roof.
Some jurisdictions require non-perforated 15-pound felt underlayment in severe climates, instead of the interlayment.
Waterproof Membrane Required Below?
No. The minimum slope is 4 in 12. If shakes are used on a lower slope, a separate waterproof membrane below would be necessary.
Common Flashing Materials
Galvanized steel, aluminum, copper, lead, lead-coated copper.
Maximum Number of Layers Recommended
One.
Life Expectancy
20 to 40 years. There are several variables including climate, pitch (slope), overhanging trees, quality of shake, installation technique, etc.
Common Failure Modes
Curling, cupping, splitting, rotting, wear-through and burn-through.
Other Details
A 15-inch starter shake is typically used.
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Laying Shakes
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The nailing pattern is the same as wood shingles. The spacing between adjacent shakes is slightly more than wood shingles (3/8 to 5/8 inch). Nails or staples should be driven flush, but not into the face of the wood.
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Exposure
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Although shakes are a looser fitting system than wood shingles, the exposure is greater. On a shingle roof, anywhere you cut through it you would find at least three thicknesses of shingles. On a shake roof, you will find two thicknesses in some areas, if you were to cut through the roof. This seems strange since the shakes are inherently a looser roofing system. It’s primarily a question of economics that led to the shakes having a greater exposure than shingles. The felt interlays help to compensate for this. Remember that shakes are thicker than shingles, so there is more material on the roof.
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