BCAB #1106 - Cedar Roof Shakes, Article 188.8.131.52.
December 12, 1989
Re: Cedar Roof Shakes, Article 184.108.40.206.
With reference to your letter of October 30, 1989, regarding the application of Article 220.127.116.11. in the Building Code.
We note the various references which have been submitted on this question of offset joints, but must conclude that the Code is being misinterpreted; the words used do lend to some confusion. Basically we take the intent as ensuring that vertical joints in any course do not coincide with such joints in the course above, a necessary factor for all unit roofing. In the case of regular sized units this would result in any joint being approximately central to the unit above; in the case of wood shakes we are dealing with units of irregular width, and we would assume that this explains the Code requirement for an offset not less than 40 mm.
Under the circumstances we consider that Article 18.104.22.168. is dealing only with consecutive or successive courses, unfortunately it uses both "adjacent" and "alternate", but the meaning is the same. Vertical joints in each course must be offset at least 40 mm from joints in the course above, which is both the adjacent and the alternate course. We do not take the provision as also referring to a third course, it only controls successive courses; we interpret the words "so that joints in alternate courses are staggered" as merely a statement of what is achieved by offsetting joints in adjacent courses, not an additional requirement.
J.C. Currie, Chair