What is the unit run measurement for a rafter that is attached to the ridge at a 90 degree angle?

The unit run measurement for a rafter attached to the ridge at a 90-degree angle is defined as the horizontal distance that the rafter spans for every unit of vertical rise. When considering a rafter set at 90 degrees, this implies that it is perpendicular to the ridge board, directly translating the rise to the run along a horizontal level. In standard framing practices, especially in North Carolina carpentry, a common run measurement for rafters is often set at one foot or 12 inches.

This standard runs true for basic constructions, enabling builders to create consistent angles in roofs, which is critical for both structural stability and aesthetic appeal. The other measurements do not conform to this standard unit run when a rafter is installed at a 90-degree angle, making 12 inches the appropriate choice for the run measurement in this scenario. Understanding this concept is essential for anyone involved in carpentry and construction, as it governs how rafters are laid out and installed effectively.