Sample HAP Calculations PLUMB LINE DEPTH = RAFTER DEPTH / cos PITCH ANGLE
Diagram detailing the relationship between rafter depth, rafter pitch angle, and total plumb line depth.
The pitch angle, given as 45° on the diagram, may actually assume any value. For a rafter depth of 11.25, and a pitch angle of 45°:
Value for the HAP returned by CAD
The sum of the angles is the rafter pitch angle, 45°
Sample Calculations
(1) Length along bottom = RAFTER DEPTH / sin PITCH ANGLE
Substituting the numbers in the diagram above:
Changing the variables:
Another example, using a rafter depth of 13.25, and a pitch of 8/12, giving a pitch angle of arctan (8/12) = 33.69007°.
Same initial variables as the last calculation, but this time solving for the plumb line depth, and factoring by 2/3.
Triangle lengths instead of trig functions:
The final pair of calculations repeated using the lengths of the 8/12 pitch triangle.
This is exactly the same as using the trig functions of 33.69007°.
Solving for the plumb line depth, and factoring by 2/3.
