A plumber is calculating the fixture unit load for a stack in a three-storey apartment building. Each floor has five apartment units, and each unit contains one bathroom (water closet, lavatory, bathtub/shower), a kitchen sink, and a laundry standpipe. What is the total drainage fixture unit (DFU) load for one typical apartment unit according to the National Plumbing Code of Canada (NPC)?

Question: A plumber is calculating the fixture unit load for a stack in a three-storey apartment building. Each floor has five apartment units, and each unit contains one bathroom (water closet, lavatory, bathtub/shower), a kitchen sink, and a laundry standpipe. What is the total drainage fixture unit (DFU) load for one typical apartment unit according to the National Plumbing Code of Canada (NPC)?

Answer options:

• 6 DFU
• 8 DFU ✅ 10 DFU
• 12 DFU

Correct answer: 10 DFU

Explanation: According to NPC Table 7.4.9.4.(1) (or equivalent provincial tables): Water closet (tank type) = 3 FU, Lavatory = 1.5 FU, Bathtub/shower = 2 FU, Kitchen sink = 2 FU, Laundry standpipe = 2 FU. Summing these values gives 3 + 1.5 + 2 + 2 + 2 = 10.5 FU. When selecting from the given options, and often for typical sizing, rounding up to the nearest common capacity is necessary, making 10 DFU the most appropriate value for a full apartment unit's drainage fixture unit load.