Saturday, December 27, 2014

Rising Purlin with Rafter Seat Cuts

Zimmerer Ausbildungs Zentrum Biberach

Pictures from the German Carpenters Training Centre in Biberach. This first task model looks small and simple enough. However, if you look closely the task model has a rising purlin, wall plate, with a plumb hip rafter, canted rafter and an inclined rafter with edge bevel. There's only a handful of Americans that can even draw out the geometry for an plumb jack rafter seat on the rising purlin.  In sticked framed roofs, I've always lower the rising purlin, wall plate, to avoid cutting the compound seat cut on  jack rafters.


Another picture from German Carpenters Training Centre in Biberach with a task model with jack rafter seat cuts on the rising purlins.


In the last task model in Bernd Kupper's book, The new Book on the ancient knowledge of Roof Framing, Pent roof with Pointed Dormer, Bernd shows a good drawing technique for developing the seat cut on the rafters on the rising purlin. 










After starting the drawings of the task model from the book, I decided to see if the drawing technique for the seat cuts on the rising purlin would work on the task model from the German Carpenters Training Centre in Biberach. I'm not sure if this was the technique that used, but it worked pretty easily for me. 











Drawings for the second task model from the German Carpenters Training Centre in Biberach using Bernd's technique.






Here's an example in a situation that I've come across before. With rafters crossing over the top of a sloping rake wall. Using Bernd's technique it makes it pretty simple to draw out the seat cuts for the rake wall, rising purlin. No more lowering the rake plates. The seat cut on the rafters crossing the rake wall, use the same angles we would use on the lower jack rafter claw on a hip rafter.













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