Dan - Glad you’ve piped in…

Gabel - Not having heard of such a roof before, I was envisioning, and thought we were discussing something more akin to a clapboard roof , only of riven boards, (A common product here in colonial times) and being on the cheap, maybe “seconds”, something that split out with a slight taper but with so-so grain, not worth dressing/planing into an a-class clapboard.

Jim – Good stuff as always. I have not seen such a batten ghost, though I have stripped more than a few Purlin roofs down to their original sheathing. But I will keep an eye out. Should be easy to spot, as I’m guessing though such a roof would only buy you a few years before it needed proper roofing lain over it, I’m also guessing the weathering between the battens, would be deep and distinct, as compared to the protected surfaces below the battens. Nor have I seen a Purlin roof sheathed RB&B style, though it is a common sheathing/siding methodology for early barns, and I’m guessing it would be a much more durable board roof than one with a batten over.

As far as close spacing of Purlins intentionally for shingles. That would be a tough one, I have lain a number of “board shingle” roofs on bridges, (Cedar ½” X 6 X 3 times the length of exposure - Common to bridges in that they have a long service life and are exceedingly light) but these still require nail-base at every exposure (11” being typ) and I’ve not seen nor heard of a board shingle being longer than 48”, which would require Purlins @ 16” OC