What is the maximum diameter of holes bored in joists relative to their depth?

The maximum diameter of holes bored in joists is established to maintain their structural integrity and load-bearing capacity. When a hole is drilled in a joist, it effectively removes material, which can alter how weight is distributed and how the joist performs under load.

The guideline that allows for holes up to 1/3 of the joist's depth provides a safe balance; it ensures that enough material remains in the joist to carry loads without compromising strength or stability. This ratio is based on engineering principles that consider both the tensile and compressive forces acting on the joist. If the hole were larger than this proportion, the risk of failure or deformation under load increases significantly.

Options suggesting smaller diameters, such as 1/4 or 1/2 the depth, could also be structurally sound, offering more conservative allowances, but do not reflect the maximum permissible size according to standard practices. The largest diameter consistent with maintaining structural integrity is thus 1/3 of the joist's depth, which is recognized in many building codes and construction guidelines.