- Q. What underlayment
should I use under cedar shakes?
A. A continuous underlayment is
not normally used under shakes. Instead, 18-inch-wide strips of
No. 15 or No. 30 felt are interwoven with the shakes. The
bottom edge of the felt strips should start twice the exposure
width above the shake butts (see illustration). For example,
with 24-inch shakes having a 10-inch exposure, the "
interlayment" should begin 20 inches above the butts. The felt
interlayment should only be nailed to the sheathing along the
At the eaves, use a 36-inch-wide No. 30 felt eaves flashing
or an ice membrane.
installing wood shakes, interweave 18-inch-wide strips of No.
15 roofing felt between each course. Nail the felt strips to
the sheathing along the top edge, and keep each strip two
exposure widths above the butt edge of the course below. This
way the felt isn’t visible in the 1/2" gaps between the