I've built 2x4 walls for my shop, and now I need to cut the bird's mouth into the rafters for the roof. I understand the concept, but I'm a bit shy on the exact details.
I will have 2x6 rafters in a vaulted ceiling (the drywall will be directly attached to the inside of the rafters until it hits the collar ties) sitting atop the 2x4 top plate. What I've designed so far has 5-1/2" of rafter left vertically at the inside edge of the wall, leaving only 3-1/4" of wood at the outside edge of the wall. Here's a drawing:
- Is this the proper way of doing it?
- Do I need to change the angle of the rafter so there is 5-1/2" of wood above the outside edge of the wall?
- Does the bottom of the rafter need to meet up with the inside edge of the top plate, leaving however much wood above that leaves?
- Is there something totally different I need to do?
- Am I over thinking this too much?
As I've been writing this up, I believe that option 3 is the correct answer. Since the ceiling is vaulted, the way I've drawn it will leave me with a short section of horizontal ceiling (about 1-1/2") at the wall because of the flats on all the other rafters not at the gable end. (Remember, this is a vaulted ceiling, drywall will be attached directly to the bottom of these rafters.) If I change the pitch of the roof to bring the bottom of the rafter to the inside edge of the wall, that will give me a nice, clean joint between the wall & ceiling finish material.