Cedar shake nailing pattern (C) Carson Dunlop Associates

Wood Shake Roof Installation Details - Photo Guide
     


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Wood shake roof installation details: here we define wood or cedar shake roofing materials & we discuss wood shake roofing installation details and good practices. Sketch at page top is courtesy of Carson Dunlop Associates. Also see WOOD ROOF INSTALLATION SPECS and see our checklist of wood shingle installation specs at WOOD ROOF INSPECTION GUIDE.

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Types of Wood Cedar Shake Roof Application Pattern Details

Wood shakes (C) Carson Dunlop AssociatesUnlike their thinner brothers, wood shakes are typically 18"to 24" in length, and up to 14" in width (more than 8" is at extra risk of future splitting).

[Click to enlarge any image]

The roofing shake thickness ranges from 1/2" to 1 1/4" where measured at the shingle butt. The maximum exposure for wood shakes is 7 1/2" (for an 18" long wood shake) or 10" (for a 24" long wood shake), and head lap is 3" or 4" respectively.

A good quality, properly-installed wood shake roof has a life expectancy of 20-40 years. Carson Dunlop's sketch shows the typical cedar shake application pattern and spacing.

  1. Taper-sawn wood shakes are sawn on both sides - like a thick wood shingle
  2. Taper split wood shakes are cut from opposing ends of a wooden block, having a shake butt that is at least 1/2" in thickness and typically are 24" in length. Uncommon, costly.
  3. Hand split, re-sawn wood shakes are similar to straight split shakes (below) but are thicker. A thick split of wood that is rough-split on both sides is re-sawn in half through its thickness to produce two thick shakes, each with a smooth back.
  4. Straight split wood shakes (also called barn shakes ) are split from the same end of a block of cedar (or other wood) and are not tapered. Straight split wood shakes are not usually used on homes.
Cedar shake nailing pattern (C) Carson Dunlop Associates

 

Here Carson Dunlop's sketch shows typical cedar shake nailing details & pattern and exposures.

Notice that for this example cedar shake roof a felt interlay is installed between every course of shakes.

More details useful for determining the condition of a wood roof are at WOOD ROOF INSPECTION GUIDE.

As we also discuss at WOOD ROOF INSPECTION GUIDE,

Wood shake exposures for wood shake roofs: the maximum weather exposure for wood shakes or wood shingles depends on the shingle size and the slope or pitch of the roof.

Allowable wood shake exposure may also vary by the shake grade - something that you might infer by visual inspection of the shakes, matching against wood shake grade definitions, or if a wood hake identification label can be located.

Roof Slope or Pitch Maximum Wood Shake Exposure on Roofs
Wood Shake Length
18" 24"
4/12 & steeper roofs 7 1/2" 10" (Note)
Note: 24" x 3/8" handsplit wood shakes are limited to 7 1/2" weather exposure, or 5" exposure where the Uniform Building Code is in application.

Shingle exposure rules for wood shingles (as opposed to shakes) are detailed at WOOD ROOF INSTALLATION SPECS.

Wood shingle or shake keyways or gaps

Wood shingle roof (C) Daniel FriedmanWood shake keyways: the gap or space between adjacent wood shingles should be between 1/4" and 3/8" in width.

For wood shakes the keyway should be 3/8" to 5/8" in width.

The Shingle Bureau points out that the gap observed between shingles or shakes on a wood roof will vary depending on ambient moisture conditions as moist wood shingles or shakes swell (which is why we need a gap, to avoid buckling and splitting).

Wood shingle keyways or gaps are illustrated at the top of this page.


Wood shake joints & gap alignment: the gaps or keyways described just above for any pair of abutting wood shakes should have a side-lap offset of no less than 1 1/2" from the joints or keyways in adjacent shake courses (horizontal rows of wood shakes across the roof), and in any three wood shake courses no two joints should be in direct alignment (gaps should not be over gaps in any three shake courses).

For added details about proper wood shake roof installation, the most authoritative source of wood shingle and wood shake information is from the Western Red Cedar Shingle & Shake Bureau (now the Cedar and Shake Shingle Bureau, since not only western red cedar is used for roof shingles).

Wood Shake Roof Installation Specifications - Best Practices

As detailed in Best Practices Guide to Residential Construction (printed text) chapter on BEST ROOFING PRACTICES,

Whether installed over spaced or solid sheathing, shakes should always be interlaid with 18-inch-wide strips of No. 30 roofing felt. The felt strips acts as baffles to keep windblown snow and other debris from penetrating the roof system during extreme weather. The felt “interlayment” also helps shed water to the surface of the roof.

It is important to locate each felt strip above the butt of the shake it is placed on by a distance equal to twice the weather exposure (Figure 2-51 shown below).

[Click any image or table for an enlarged, detailed view.]

Figure 2-51: Wood Shake installation details (C) J Wiley, S Bliss

Placed higher, the felt strips will be ineffective. Placed too low, they will be visible in the keyways and will wick up water, leading to premature failure of the shakes. In addition, follow these guidelines:

  • For the starter course, use either a single layer of shakes or two layers separated by a strip of felt interlayment (installed up from the eaves by a distance equal to the weather exposure). Fifteen-inch shakes are available for the bottom layer of a double starter course Each shake gets two nails about 3/4 inch in from each end and 1 1/2 inches above the butt line of the overlaying shake.
  • The first course should overhang the fascia by 1 1/2 inches.
  • All courses should overhang the rake trim by about 1 inch.
  • Leave a gap between adjacent shakes of 3/8 to 5/8 inch for expansion when wet.
  • Offset joints in successive courses by at least 1 1/2 inches

-- Adapted with permission from Best Practices Guide to Residential Construction.

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