Notches in the top or bottom of joists should not exceed what fraction, and cannot be located in which portion of the span?

Notches in the top or bottom of joists are subject to specific limitations to ensure the structural integrity and load-carrying capacity of the joists. The correct fraction that notches should not exceed is one-sixth of the depth of the joist. This is crucial because excessive notching can weaken the joist, making it more susceptible to bending, failure, or cracking under load.

Moreover, the location of these notches plays a significant role in maintaining the strength of the joist. Notching should not be done in the middle portion of the span, as this area experiences the highest tensile and compressive stresses when the joist is loaded. Notching in this critical area could significantly compromise the joist's performance under typical loading conditions, hence the specific guideline that notches must be kept out of the middle section.

Understanding these limitations is essential for proper framing practices to avoid inadvertently compromising the safety and stability of the structure.