This CutIn Dormer Shed Roof Rafter Calculator will return the roof framing trigonometry & geometry details for:

  1. Dormer Shed Roof Rafter Length
  2. Dormer Shed Roof Miter Angle (Rake Cut Angle)
  3. Dormer Shed Roof Run
  4. Main Roof Rafter Intercept Length
  5. Dormer Intersect Length For Lapping Rafters
  6. Intersecting Roof Slope Angle




Intersecting Roof Slope Angle = arctan((Main Pitch - Dormer Pitch) ÷ 12) 
Dormer Height = Dormer Height Above Main Roof + Dormer HAP
Main Roof Rafter Intercept Length = (Dormer Height ÷ tan(Intersecting Roof Slope Angle) ) ÷ cos(Main Roof Pitch Angle)
Dormer Run = Dormer Height ÷ tan(Intersecting Roof Slope Angle)
Dormer Rafter Length = Dormer Run ÷ cos(Dormer Roof Pitch Angle)
Dormer Miter Cut Angle =  Main Roof Pitch Angle - Dormer Roof  Pitch Angle