You will need to use compound miter cuts for the cricket rafters.
Framing and roof crickets.
In this example a pitch of 12 12 and 1 1 2 x 5 1 2 rafters are specified.
Do not check build roof planes.
This is the number which we will use to lay out our rafter for the cricket.
Secure the plywood triangles to the roof decking and cricket ridge with galvanized screws.
Put metal flashing along the sides of the cricket nailed in place to overlap seams with the roof.
2x8 sleepers should be nailed to the roof surface to pick up the ends of the rafters.
Always frame the cricket at the same pitch as the roof and you will be within code guidelines.
Install a waterproof membrane over the cricket sides and edges fastened to the cricket with a construction stapler.
This also makes it easier.
This beam will provide the backbone for the cricket or saddle.
Ok so a four foot wide chimney has a span of 4 foot and half of that is the run which is 2 foot.