What is the maximum allowable depth for drilled holes in floor joists or rafters?

The maximum allowable depth for drilled holes in floor joists or rafters is one-third of the depth of the member. This guideline is established to ensure the structural integrity of the joists or rafters is not compromised. When holes are drilled into these structural components, the material can lose strength, particularly if the hole is too large or placed in an area where it can undermine the structural capacity.

Drilling holes up to one-third of the depth allows for sufficient material to remain, providing the necessary support and reducing the risk of failure due to the loss of material. This standard is based on common engineering practices that consider factors such as load-bearing capabilities and safety margins.

Other options suggest different limits, such as one-fourth, two inches, or one-half of the depth, but these do not align with established guidelines for maintaining structural integrity while facilitating necessary modifications to joists and rafters for plumbing, electrical, or other installations. Adhering to the one-third rule helps ensure safety and performance in the building's framing system.