What is the total length of the common rafters for the specified roof structure?

To determine the total length of the common rafters for the given roof structure, it's important to understand the variables that contribute to this measurement, such as the pitch of the roof, the span between the walls, and any overhangs used in the design.

The length of a common rafter can be calculated using the Pythagorean theorem if the rise and run dimensions are known. The total length of the rafters will be twice the length of one rafter since there are usually two rafters for each section of the roof (one on each side).

In this case, if the calculations, which take into account the rise of the roof and half the span (or total run), lead to a result of 18.90, it indicates that the common rafters were approximated in a way that considers both the structural requirements and the roof's aesthetic shape. Additionally, the calculations would typically include any adjustments for the rafter tail if an overhang is applied.

Therefore, the total length of the common rafters being 18.90 is based on accurate measurements using the dimensions of the roof structure and applying principles of geometry effectively.