For our 4 x8 lean to example using a 2 4 rafter the depth of the birdsmouth is limited by the 1 3 depth of the rafter rule.
Framing a shed roof with a valley.
Use a framing square to help lay out the notch based on the slope of the roof.
Add the length of the overhang beyond this mark and.
That is except for the crowning glory the shed roof.
To transition the eaves the horizontal fascia extends to the last rafter tail and a vertical return finishes the transition.
Sheathing blocking is added along the valley and the sheathing pieced in for both roof planes.
A 2 4 wall with a 2 6 rafter can be notched for a 4 seat.
On the common rafters the plumb cut is marked with a framing square for a 12 in 12 pitch 45 and cut square i e no bevel.
Position the square at the end of the rafter board with the tongue on your left and facing away from you.
In truth framing in the foundation and the walls adding doors and windows these are all relatively straightforward simple tasks.
The valley rafter is marked for a 12 in 17 pitch and then cut with a double bevel to fit into the ridge intersection.