Where are notches prohibited in a joist span?

The prohibition of notches in the middle third of a joist span is primarily based on structural integrity and load distribution. Notching is a method used to create space in wood members for plumbing, wiring, or fixtures. However, notching the middle third of a joist can significantly weaken the joist and reduce its ability to carry loads effectively.

The middle section of a joist is where the maximum bending moment typically occurs when the joist is loaded. By notching this critical area, the risk of failure increases because the joist's tensile strength and ability to resist bending are compromised.

In contrast, notching is often permitted at the ends of a joist (the end quarter) and sometimes near support beams, as those areas experience different structural stresses, particularly compression. These regions have more material to safely accommodate notches due to their positioning and the nature of the loads they carry.

Understanding the implications of joist notching and where it is allowed ensures that structural integrity is maintained, preventing issues like sagging or failure in a home improvement context.