What is the maximum distance from either end that joists should not be notched?

Joists are critical components in a building's structural framework, acting as the horizontal supports for floors, ceilings, and roofs. Notching a joist can affect its load-bearing capacity, so it is essential to adhere to certain guidelines to maintain structural integrity.

The correct answer, which specifies that notching should not occur within the first third of the span, is grounded in the principles of load distribution and structural safety. Notching within this region can significantly weaken the joist because this area typically experiences the highest stress and bending moment when loads are applied. By prohibiting notching within the first third of the span, builders ensure that the joist retains its strength where it is most needed.

In contrast, options suggesting distances such as 12 inches or half of the span do not account for structural requirements and could lead to reduced load-bearing capacity if not followed properly. Therefore, recognizing the critical stress distribution throughout the joist span underscores why the specified limit of not notching within one-third of the span is both appropriate and necessary for ensuring the stability and safety of the construction.