Prefitting an 8' gable dormer

If a timberframe is to have dormers, we feel that they should be framed with timber, not "left for the carpenters" to fill in . The dormers may cost a little more initially, but they can be sheathed in quickly and easily, without the head scratching involved in trying to form a valley where there is nothing to work with.

We make our valleys with a "backing cut", the "V"ed out section that forms the intersection of the main roof and the dormer roof. This makes it very straightforward for the carpenters to sheath, insulate, and shingle the dormer.

These are the 2 valley rafters for the dormer. Note the "backing cut" on the right one.
Valley on the right, cripple rafter underneath (in the plane of the main roof), dormer top plate on the left.
Another view looking up the valley. The top plate (on right) will be horizontal in the finished roof.
The valley is cut to allow the top face to project over the top plate (right) so as to not leave an empty space.
Another view.
Looking down the valley.
Another view.

With jack rafter in place. Right: in the raised frame.
Below: jack rafter tenons.