Wood shakes must be installed on roof slopes of 3:12 or greater and must be installed in accordance with the manufacturers installation instructions and the code.
Wood shakes must be laid with a side lap of not less than 1½ inches between joints in adjacent courses.
Spacing between shakes in the same course must be between 1/8 inch and 5/8 inch for shakes and taper sawn shakes of naturally durable wood and ¼ inch and 3/8 inch for preservative taper sawn shakes.
Fasteners for wood shakes must be corrosion resistant. Shakes must be attached with two fasteners per shake. Fasteners must be positioned not more than 1 inch from each edge and not more than 2 inches above the exposure line.
The starter course at the eaves must be doubled and the bottom layer may be 15-inch, 18-inch, or 24-inch wood shakes or shingles. Fifteen-inch or 18-inch wood shakes may be used for the final course at the ridge. Shakes must be interlaid with 18-inch-wide strips of No. 30 felt shingled between each course in such a manner that no felt is exposed to the weather by positioning the lower edge of each felt strip above the butt end of the shake it covers a distance equal to twice the weather exposure. Underlayment must comply with ASTM D 226, Type I.