Birdsmouth Cut Calculator
Construction & Home ImprovementCalculate the heel depth and cutting angles for a birdsmouth seat cut where a rafter meets the wall plate.
Heel Cut Depth
Depth of the notch cut into the rafter where it sits on the wall plate.
Plumb Cut Angle
30.0
Angle of the vertical plumb cut, equal to the roof pitch angle.
Level Cut Angle
60.0
Angle of the horizontal seat cut, the complement of the pitch angle.
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Creators
Odeh Ahwal0people find this calculator helpful
Views
Helpful
Saved
Embeds
Construction & Home Improvement calculators
Frequently Asked Questions
What is a birdsmouth cut?
A birdsmouth cut is a notch cut into the underside of a rafter so it sits securely on top of the wall plate, with one horizontal seat cut and one vertical heel cut, distributing the roof load evenly onto the wall.
How deep should the heel cut be?
A common guideline is to cut no more than about one third of the rafter's depth to avoid weakening it excessively. Check this calculated heel depth against your actual rafter depth before cutting.
Why do the plumb cut and pitch angle match?
The plumb cut, the vertical face of the birdsmouth and the rafter tail, is by definition cut parallel to the ridge-to-wall slope line, so it shares the same angle as the roof pitch itself.
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