When one roof is framed on top of another, already existing roof, this type of roof framing is sometimes called "California" roof framing. I refer to the roof that is framed first as the "existing roof" and the roof that will be framed on top of it as the "California roof". Sometimes I sheath the existing roof before framing the California roof and also add a "flat valley board", ( usally a 2" x 12" ) to nail the California jack rafters to. Other times, I nail the flat valley board directly to the top of the existing roof rafters and add blocking for the plywood at the valley.
I'd like some feedback from you guys who do a lot of this type of framing. Do you Always, Sometimes, or Never sheath the existing roof before framing the California roof? Is it required by the building codes in your area? Do you add a flat laydown valley board to nail the California jack rafters to, or do you nail them directly to the plywood sheathing? If you use a flat valley board, what type of stock do you normally use for it? Do you ever nail the valley board directly to the top of the existing rafters? If so, do you add blocking at the valley?
In your area, what other names are used for this type of roof framing besides "California"? Also, in south Texas, you don't "sheath" a roof, you "deck" it. What do you call this process in your area?