Jan Lewandoski gave me the all clear to post this. His comments are in response to my query on CGs and the Vermont barn census.
Funny, but even he can only speculate about the origins of this typology.
Dear Don, These barns are common in northern Vermont and perhaps elsewhere as well. Sometimes I refer to them as having an interrupted plate, or a segmental plate, but in truth they are connecting girts since rafters rarely , though sometimes , land on them. A flying or eaves purlin is a necessary accompaniment and that may carry rafters in between the principal rafters that tenon into the tie beams crossing the post heads. I date most of them 1840-1880. It perhaps makes assembly easier since it is just a question of connecting bents, no pulling up long scarfed plates. Maybe that is the origin, the tendency to build barns longer than available plate stock (40-50 ft.) and a suspicion of scarfs or trying to avoid the complex joinery and erection. Unfortunately the barn census is necessarily being done by volunteers who will have various abilities to interpret arcane framing details. However, I have suggested that each surveyor take a photo of the top of a wall post, and examining these can give us this answer.
