How To Cut Roof Rafter Birdsmouth

The plumb or ridge cut is made at the top of the rafter.

How to cut roof rafter birdsmouth. Calculate the pitch of your roof. Set the framing square on top of the rafter beam with the tongue facing the top of the rafter. Choose which end of your rafter you want to be the top. Make a mark along the top edge of the rafter where this measurement ends.

If the roof has a 30 degree pitch the underside of the rafter and the vertical cut of the birdsmouth form a 120 degree angle. A birdsmouth cut in a rafter measures the same angle as the pitch of the roof. Rise is the vertical distance from the top plate of. Measure and mark plumb cut.

How to cut a birdsmouth joint calculating the pitch of a roof and making ridge cut. Use the square root figure to measure along the top of the rafter. Use a square placing one side against the plumb cut line. Mark the plumb cut at the top of the rafter.

How to cut bird s mouths in rafters step 1. 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. Take a break from the measuring by cutting the top end of the rafter first. 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.

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. Pitch rise run x 2. This new line marks the horizontal cut for the bird s mouth. This ensures that you make the birdsmouth cut at the right length in the rafter.

The result of this equation represents the. Multiply your pitch by 24 to determine the rise per foot of run. Calculate rafter or joist length to birdsmouth location. The cut itself measures 90 degrees in order to rest snugly on the right angle of the wall plate.

With your ridge cut or plumb cut made you are now all set to. Simple jig to cut your birds mouth notches.