Notches in solid sawn lumber ceiling joists should not be located in the middle what fraction of the span?

The correct choice indicates that notches in solid sawn lumber ceiling joists should not be located in the middle third of the span. This guidance is rooted in structural engineering principles.

Notching in the middle section of a joist can significantly weaken its structural integrity because this area experiences maximum tension and bending stress when the load is applied. By avoiding notches in the middle third of the span, builders maintain the joist's strength where it is most needed, minimizing the risk of failure or sagging.

While notches may be permissible in other areas of the joist, particularly towards the ends where loads are typically lower, this specific guidance ensures that the critical zone – where most stress occurs – is left intact to support the weight and loads effectively. Understanding these guidelines not only enhances safety but also contributes to the longevity and performance of the structural system.