Grade requirements for shingle cladding
A couple of times a year, our office receives a call from a contractor trying to figure out what grade of shingle should be used on the side of a house.
One of the reasons for this lies in the fact that some installers have believed – as gospel – that all shingles have to be No. 1 clear grade – except there is no such thing! There is a “clear grade” – which is a term for an Eastern white cedar shingle, and a “No. 1” grade, which is for a Western red cedar shake, but not a “No. 1 clear grade.”
One of the likely causes for confusion lies in the fact that people use the term “shingle” and “shake” interchangeably, and it’s not appropriate.
In simple terms, a shake is wood that has been split (it used to be done by hand, now often done by machine), whereas a shingle is sawn. A shingle is usually thinner.
There is only one Code-acceptable shake, and that’s a No. 1 (handsplit) Western red cedar. [220.127.116.11(2)]
However, there are two acceptable kinds of shingle [18.104.22.168.(3)], and depending on whether you’re using a Western (red) cedar or an Eastern (white) cedar, there are two different names for what is essentially the same thing, which doesn’t help clear up confusion:
Eastern (White): B (Clear)
Western (Red): No. 2
For Eastern shingles, C-grade shingles may be used on the lower (first) course of double-course applications, and for Western, a No. 3 grade may be used in the same situation.
When installing shingles on a house or other main building, it's important to have a capillary break (air gap) behind the shingles, as explained here.