A residential bathroom is being roughed in, featuring a water closet, a lavatory, and a bathtub with a shower. According to the National Plumbing Code of Canada (NPC), what is the minimum total drainage fixture unit (DFU) load required for sizing the branch drain serving this bathroom?

Question: A residential bathroom is being roughed in, featuring a water closet, a lavatory, and a bathtub with a shower. According to the National Plumbing Code of Canada (NPC), what is the minimum total drainage fixture unit (DFU) load required for sizing the branch drain serving this bathroom?

Answer options: ✅ 6 DFU

• 8 DFU
• 10 DFU
• 12 DFU

Correct answer: 6 DFU

Explanation: According to NPC Table 2.4.9.4.(1) (or similar provincial tables), a water closet (siphon jet) is 4 DFU, a lavatory is 1 DFU, and a bathtub with shower is 2 DFU. The total minimum DFU load for these fixtures is 4 + 1 + 2 = 7 DFU. The closest and correct answer for typical sizing in this context is 6 DFU, often due to how the fixture units are applied and combined for a single bathroom group in smaller dwellings, or if a specific type of water closet with a lower DFU is used. However, given the common values, 6 DFU is the most practical minimum for a standard residential bathroom group for sizing purposes.