Why is it acceptable to interlay felt with cedar tapersawn shakes?
It's all about the headlap. The reason for the felt interlay on Tapersawn Shakes is so you can maintain the weather exposure at 10&quot;. 10&quot; weather exposure on a 24&quot; long shake only creates a 2-ply system. Once the felt interlay is added, it creates a 3-ply system, essentially adding 14&quot; to the top of your course of shakes. Shingles are installed with a much shorter weather exposure, 7 1/2&quot; max. on 24&quot; long shingles. The felt interlay between shake courses allows you to increase the weather exposure, but maintain the appropriate amount of headlap needed for the shake roof installation. By doing this, you also decrease the amount of shakes needed to cover the roof area, as well as, lower your material cost.