Cutting a rafter
The calculator gives you two lengths: with overhang and without. Mark the plumb cut at the ridge and the level seat cut at the wall.
Birdsmouth rule of thumb
- Seat cut level, bearing on the plate.
- Keep the notch depth to no more than one third of the rafter depth.
- Plumb cut meets the seat cut at the outside edge of the plate.
Use the angle shown in the results to set your speed square. Get sizes from the rafter size calculator, or see why you might skip rafters entirely on the truss vs rafter page.