How is the angle of a plumb cut determined?

The angle of a plumb cut is determined by the unit of rise, which refers to the vertical distance that the rafter rises for a given horizontal run. Understanding how much the rafter ascends compared to how far it extends horizontally allows builders to establish the proper slope of the roof. This angle is critical to ensure that the roof surfaces effectively shed water and maintain structural integrity.

The unit of rise is essential in calculating angles for roofing because it directly affects the pitch of the roof; a steeper pitch results in a different plumb cut angle compared to a flatter roof. This relationship makes it easier to determine where a rafter will meet the peak of the roof, ensuring it fits correctly with the other framing components.

The other options would not yield the correct angle for a plumb cut because they focus on aspects unrelated to the geometry necessary for determining the rafter's angle. For instance, while total rise does contribute to understanding roof pitch, it does not alone determine the specific angle of the plumb cut without considering the unit of rise.