A plumber is installing a 2-storey residential drainage system. A kitchen sink is located on the main floor and will discharge into a 50 mm branch drain. What is the maximum developed length permitted for the unvented portion of this branch drain, according to the NPC?

Question: A plumber is installing a 2-storey residential drainage system. A kitchen sink is located on the main floor and will discharge into a 50 mm branch drain. What is the maximum developed length permitted for the unvented portion of this branch drain, according to the NPC?

Answer options:

• 1.5 m
• 2.5 m ✅ 3.0 m
• 3.5 m

Correct answer: 3.0 m

Explanation: According to NPC Table 2.4.9.4.(1) 'Maximum Developed Length of Unvented Branch Drains and Fixture Drains', for a 50 mm branch drain, the maximum developed length permitted for the unvented portion is 3.0 m. This ensures proper drainage and prevents trap siphonage or back-pressure. Options such as 1.5 m or 2.5 m are too short, and 3.5 m would exceed the code-prescribed limit.