The deflection of floor joists should not exceed:

The deflection of floor joists is a critical factor in ensuring the structural integrity and performance of a floor system. A common guideline adopted in the construction industry states that the maximum allowable deflection for floor joists under live load conditions should not exceed 1/360 of the span. This means that if you take the total span of the joist, the deflection under load should not be more than one part in 360 of that total length.

This guideline is important because excessive deflection can lead to a range of problems, including structural issues, discomfort for occupants, and cracks in finishes or walls above. The 1/360 limit allows for a balance between performance and safety, aiming to maintain a level floor without noticeable sagging that could affect both aesthetics and functionality.

The other options represent alternative tolerances that do not align with the accepted standard for resident spaces. While 1/36 may seem reasonable in specific applications, it is significantly larger than the acceptable limit and could lead to uncomfortably noticeable deflections. Both 1/2" and 3/4" are absolute measures that do not correspond to the span of the joist, which varies widely in construction applications. Such fixed amounts could lead to unsafe conditions depending on