Oxfordshire Woodland Group

The third week of the cruck building course has concentrated on the layout and cutting of the gable frames (one full one half hip) and the roof.

The layout of a timber-framed roof requires a considerable knowledge of geometry and trigonometry. Unfortunately very little has been written on this topic with much of this historically having been learned first hand "on the job", however, an insight into this topic can be gained by examination of Steve Chappell's book "Advanced Timber Framing" which contains significant content relating mainly to the North American timber-frame building resurgence much of which is based on the use of computer aided design (CAD) to establish component lengths & angles. In stark contrast is the French book by Emery which is based very much on the use of full scale developmental layout techniques together with trigonometric calculation methods with this book having been written very much in the pre CAD era. For further web based information on roof layout gemetry check out Sim Ayers SBE Builders Blogspot where his extensive layout geometry book list can be found.

Unfortunately (for some) Emery's book is written entirely in French with no translation into English given however regardless of this the drawing illustrations are so good that it is quite possible to follow the logic required to layout, mark & cut quite complex compound (i.e. not plane frame) structures.

The effects of this confusing subject can been seen on the faces of the carpentry students as they listen intently to instructor Henry Russell on what was a miserably cold wet day at the end of May.

The theory was then put to the test in "lofting" or full size lay out of half hip rafter geometry on a plywood sheet.

Only the hip rafters were precut in the workshop with any oblique or birdsmouth cut jack rafters being measured, cut, fitted and then nailed into position on site after raising the frame.

No such complex thought is needed for laying out, marking & cutting the gable end rafters & gablet.

The gablet secures the ridge piece in position and will provide a landing for the central half hip jack rafter.

Ken Hume
Executive Trustee - Oxfordshire Woodland Group

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