Irregular Valley Jack Rafters
Compound Angle Calculations

12/12 Main Jack Rafters
 Jack Rafter Side Cut Angle = 46.68614° 90° - Common Rafter Pitch Angle = 45.00000° Blade Bevel along parallel to Valley Trough Line = arctan (sin 46.68614° ÷ tan 45.00000°) = 36.03989° = Backing Angle Blade Bevel along Plumb Line = arctan (sin 45.00000° ÷ tan 46.68614°) = 33.69007° = Plan Angle Angle created on Jack Rafter Face meets plumb Face of Valley = arccos (cos 45.00000° × cos 46.68614°) = 60.98286° = Complement of Valley Pitch Angle

8/12 Dormer Jack Rafters
 Jack Rafter Side Cut Angle = 29.01714° 90° - Common Rafter Pitch Angle = 56.30993° Blade Bevel along parallel to Valley Trough Line = arctan (sin 29.01714° ÷ tan 56.30993°) = 17.92021° = Backing Angle Blade Bevel along Plumb Line = arctan (sin 56.30993° ÷ tan 29.01714°) = 56.30993° = Plan Angle Angle created on Jack Rafter Face meets plumb Face of Valley = arccos (cos 56.30993° × cos 29.01714°) = 60.98286° = Complement of Valley Pitch Angle