Holes bored in joists for piping or wiring should not be larger than what fraction of the joist depth?

Holes bored in joists for piping or wiring should not be larger than what fraction of the joist depth?

• A. One-sixth
• B. One-half
• C. One-third
• D. One-quarter

Answer: (C)

Holes bored in a joist remove material that carries bending loads, so the opening must be limited to keep enough wood around it to resist forces. The largest hole that can be safely bored is one-third of the joist depth. This fraction provides a balance between giving you room for piping or wiring and preserving enough cross‑section to avoid excessive flexing or failure under load. For best results, place the hole in the middle portion of the depth and avoid edges where the wood is weakest. If a larger opening is needed, or multiple holes are required, alternative routing or reinforcement should be considered. The other fractions would be more restrictive (one-sixth or one-quarter) or unsafe (one-half) for typical joists.

Holes bored in a joist remove material that carries bending loads, so the opening must be limited to keep enough wood around it to resist forces. The largest hole that can be safely bored is one-third of the joist depth. This fraction provides a balance between giving you room for piping or wiring and preserving enough cross‑section to avoid excessive flexing or failure under load. For best results, place the hole in the middle portion of the depth and avoid edges where the wood is weakest. If a larger opening is needed, or multiple holes are required, alternative routing or reinforcement should be considered. The other fractions would be more restrictive (one-sixth or one-quarter) or unsafe (one-half) for typical joists.