When notching traditional timber joists in preparation for the installation of pipework, what is the maximum depth of notch allowed under building regulations?

• A. 1/8th
• B. 1/4
• C. 1/12
• D. 1/6

Answer: (A)

Notching a timber joist removes material that carries bending loads, so the deeper the notch, the weaker the joist becomes. Building regulations cap how deep a notch can be to keep enough cross‑section and strength for load paths, reduce the risk of cracking, and maintain structural integrity. For traditional timber joists, the maximum notch depth permitted is one‑eighth of the joist depth. Keeping the notch within this limit ensures you can pass pipework without compromising the joist. If more clearance is needed, use alternative routing or reinforcement and consult relevant regulations or a structural professional.