#1 Medium Hand Split Shakes are the least performing (shortest life-span) Cedar Roofing product when compared to #1 Cedar Shingles or #1 Heavy Hand Splits. The reason is thickness (only 1/2"), up to 20% flat-grain and only 2.4 ply with the standard 10" exposed.
A #1 Shingle has a more stringent grading standard with 100% vertical-grain fiber required instead of 80% vertical-grain required with #1 Shakes. The other reason a #1 Shingle out performs a #1 Medium Shake (even though it's thinner at the butt) is the exposure is less, so it is triple ply instead of 2.4 ply.
Example given: Standard exposure on a 16" Shingle is 5" (therefore, 3-ply) whereas standard exposure on a 24" Shake is 10" (therefore, 2.4 ply).
We prefer selling Premium Shakes; they are a step above #1's and are required to have 100% vertical-grain. This grain orientation is the most stable, thereby greatly reducing cupping and splitting and extending the life-span of your Cedar roof.