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Roof Rafter
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Rafter Calculation Formulas
Rafter Rise = Rafter Run × tan(Roof Angle)
Rafter Length = Rafter Run ÷ cos(Roof Angle)
Total Length = Rafter Length + Overhang ÷ cos(Roof Angle)
Ridge Cut Angle = 90° - Roof Angle
Tail Cut Angle = Roof Angle
Birds-mouth Length = √(Plumb² + Seat²)
Rafter Length = Rafter Run ÷ cos(Roof Angle)
Total Length = Rafter Length + Overhang ÷ cos(Roof Angle)
Ridge Cut Angle = 90° - Roof Angle
Tail Cut Angle = Roof Angle
Birds-mouth Length = √(Plumb² + Seat²)
Note: Allow for ridge thickness when determining rafter run to outer wall. Check local regulations for appropriate sizes.