||03-05-2011 10:52 PM
Of course the false dormer framing will be tied in to the roof framing; I assume you want to leave an existing gable roof framing with sheathing in place. You can frame the false dormer by laying plates onto the roof sheathing to which you will nail your rafters and wall studs. It is beyond my writing skills to explain adequately in a relatively small space how to do this. You should be able to find a diagram somewhere online or in a book and if you have a moderate level of skill I think you will be able to figure it out from the diagram. There is a load factor involved, so depending on the existing rafter size, spacing and span you may have to sister a couple of them before you start your false dormer. When determining if the rafters are adequate to support the load, just don't think about complete failure of the structure but also consider the long term affects of imposing the additional dead load; e.g. sagging of the rafters. Good Luck.