Step-Lap Rafter Seat for broken-back gable roof

[SideAffects]

I’m trying to design a lean-to attached to a 12x16 shed and I’m not sure how the two different rafters (the ones at different pitches) attach to the top plate. I was going to go with the step-lap rafter seat (probably 10:12 pitch) for the frame but then do a ~6ft addition similar to the one illustrated on page 141 (“Making the Frame Smaller”) of Learn to Timber Frame. I have a few books on the subject but details of that joint are eluding me.

I found some examples in Timber Framing 59, page 15
https://www.nps.gov/subjects/ncptt/upload/V-Roof-Joinery-Excluding-Trusses.pdf
But only one example (fig 36) shows a reduced change in pitch but without joinery at the plate. I was hoping to try to do something a little more symmetrical (the lean-to appearing to exit on the outside face of the plate, rather than from on top of the rafter)

I did find this option, on TFHQ: https://timberframehq.com/witches-hat-rafter-detail/

Regardless, there are several drawings of the cabin in the book with the lean-to roof coming off of the plate, but no joinery details. I have access to several of the more popular "learning to timberframe" books through my library so if someone has a reference to one.

[Jim_Rogers]

We use drawing # 36 with timberlok screws to secure the lean-to rafter to the main rafter.

Jim Rogers

[SideAffects]

I think that might be the route I have to go - the drawings in the book seem to suggest that some kind of joinery is happening at the plate, but maybe it is an oversight

[Don P]

 These were in my gallery. I don't think there is a decent closeup pic of any of these shed rafters on 2 barns. They have a birdsmouth top and bottom, the one at the bottom is fully supported, the one at the top is fully hanging, do not go deep up top if you go this route it wants to generate a check from that hanging corner.



 

 

 

 

 

 

[HousTony]

SideAffects: I’m glad you asked about this as I have wondered the same thing. I did find a video called the story of the carriage barn done by barnyard store (in CT I believe) that briefly shows assembly, and a software drawing, but it’s not much help…and the view of the lean-to rafter cut is not very clear.  PM me your email address if you want the screen shots I took.

Also, if you have not seen it yet, Brian_Weekly has an excellent post covering his barn raising which features use of the approach in fig 36.

Keep us updated on the direction you go.

Regards,
Tony