Which part of a joist is prohibited from being notched?

The middle part of a joist is prohibited from being notched due to structural integrity and safety concerns. Notching in the middle can significantly weaken the joist, as this area bears much of the load during service. The middle of the joist is designed to maintain its strength and stiffness under loads, and removing material from this section compromises its ability to carry weight effectively.

In construction codes, such as those found in most building regulations, notching is often allowed at the ends of joists, where stress is lower, and such modifications do not impact the ability of the joist to support loads. Notching at the top and bottom of the joist can also be permissible within certain limits, as long as it is done according to prescribed guidelines that ensure sufficient material remains to support the loads applied.