Well what is it? Is it a ridge where the rafters connect perpindicular to their pitch? Does it look like a pentagon where it is pulled at the midsection down? I definitely don't know the origin but I am interested in it nevertheless.
We have cut pentagonal ridge beams where one plane followed level, two planes were plumb and the remaining two planes followed the slope of the roof. Unfortunately I don't have a decent picture with detail that I can post.
And I have seen drawings where two faces of the beam were perpendicular to the rafter slopes rather than plumb. To my thinking this would be preferred ... cut square whenever possible.
