: In the process of building a 24'x36' single story timber frame with dropped ties and continuous top plate. Two thirds of the roof will be 2x8 common rafters, but the last third will be 6x8 principle rafters with purlins to allow for a king post truss on the gable end (please correct me if I got the rafter terminology wrong). Roof pitch is 8/12, Vermont snow loads, and rafters will be step-lapped into the plate to create an overhang.
My question comes at the joinery around the king post truss, which will span the full 24' width of the building.
I have assumed that the dropped tie (8" below bottom of the plate) used for the rest of the building would not be the best design for the free spanning kp truss - I read somewhere that the extra forces exerted by the rafters at the plate could be problematic - but if this assumption is wrong, then that makes things easy!
In "Historic American Timber Joinery", this is the only end-post tying joint that seemed to allow for a step lap:
My worries with that joint are that it: (1) is difficult to assemble (requiring the top plate to be slid on from the side); and (2) if there is significant horizontal thrust on the step lapped plate, then it is only 1 pin holding it to the tie.
So, I then thought about a raised bottom chord, but could not find any good information about proper joinery for a span of this size (I saw some other threads on much smaller structures being ok). I am mainly be worried about the strength of the tension joinery.
My current idea is a "raised chord" that is raised just enough rest on top of the plate, but is tenoned into the rafter. Because of the 6x8 rafter and 8x8 tie, there would be extra wood for the pegs to hold onto.
I would love to hear your thoughts about solutions and/or historic precedent for this type of joint. Thanks!