Make one rafter that has the bird s mouth cut in place and extends out past that for your roof overhang test fit it in place and mark it pat for pattern rafter to use in cutting its sisters.
How to cut a birdsmouth in a roof rafter.
In my photo above the green rafter line length is from the plumb cut face or ridge board face to the plumb cut face of the bird s mouth notch.
Subtract half the width of the ridge board beam in this case 0 5 inches.
Due to the width.
Divide the width of building by 2 e g.
Measure and mark plumb cut.
This point is the start of the bird s mouth.
Make a mark along the top edge of the rafter where this measurement ends.
This ensures that you make the birdsmouth cut at the right length in the rafter.
Draw a line at right angles to the bird s mouth plumb cut starting 3 inches up from the bottom of the rafter but no more than half the thickness of the rafter.
With the ripped strip installation there would be no horizontal bearing surface to resist that force.
The ridge cut also called the plumb cut at the top of the rafter the birdsmouth cut which itself comprises 2 different cuts where the rafter meets the building s wall and the tail cut at the base of the rafter.
Calculate rafter or joist length to birdsmouth location.
This new line marks the horizontal cut for the bird s mouth.
Use a square placing one side against the plumb cut line.
A lot of force is transferred down the length of the rafter and the seat cut on the birdsmouth transfers that force directly to the top plate.
Use the square root figure to measure along the top of the rafter.
Granted a structural ridge can lessen the amount of force on a rafter but even then i would.
Take a break from the measuring by cutting the top end of the rafter first.
72 inches wide divided by 2 36 inches.
When you cut the rafters you ll need to make 3 separate cuts.
Possibly the most satisfiying part of the roof yet.
