wait a minute...
So what about the semi-round rafters and joists?
They were left round to save on labor, yes? Plus, doesn't the extra diameter of these semi-round pieces add to their strength?
Though a joist pocket may be only 4 X 5 or so, the cross section of the joist itself may be a full 8 inches, which is nice and strong, sapwood and all. I see many semi-round pieces in old frames.
