How to extend eaves

[Momatt]

I have plans for a three bent frame I purchased from Grand Oaks timberframing based on someone on the forum's suggestion.   In his design, the principal rafters  are mortised into the bent post with dovetailed purloins connecting each bent.  If you want to have a roof overhang, how is it accomplished? 

[Don P]

Correctly, request a detail. If possible I'd probably extend the purlins over the gables and run the sheathing boards long over the walls to provide eave overhangs. If the loads or overhangs are greater brackets would work.

[Brad_bb]

One thing I learned is that it's preferable to stop your rafters at the outside wall of the frame.  If you want to see the rafters/rafter overhang, add rafter tails to the outside(with structural screws).  I learned that with a through rafter, it's difficult sealing around the rafter to prevent an air leak.  It's much easier and cleaner to stop the rafter and seal up your building.  Then add rafter tails to the outside.

[Momatt]

Thanks, is that what is called a sprocket timber? That will probably work. I think the joinery of the rafter to a post instead of a tie beam is unusual. My plans show a principal rafter joined to the post at each bent with purloins between

[Don P]

Not really, check Sobon's "Historic American Timber Joinery" for pics of sprockets.

[logman]

My designer refers to them as "Jet blocks".