Massachusetts Plumbers Journeyman Practice Exam

What is the minimum required number of fixture units for a residence (house)?

1. 5 DFU

2. 7 DFU

3. 10 DFU

4. 15 DFU

The correct answer is: 10 DFU

The minimum required number of fixture units for a residence is 10 Drainage Fixture Units (DFU). This standard is based on the plumbing code and the typical usage of fixtures in a household. The calculation of fixture units considers the potential load that each fixture will impose on the drainage system. In residential settings, common fixtures include sinks, toilets, and bathtubs, each contributing to the total DFU count. By establishing a baseline of 10 DFU, plumbing codes ensure that the drainage system is designed to handle the capacity and prevent overloading, which could lead to plumbing failures or backups. In comparison, other lower values such as 5, 7, or 15 DFU would either underestimate the average use or overestimate the needs in rare scenarios, which is why they do not meet the established minimum for typical residential plumbing systems. The 10 DFU threshold effectively balances adequate drainage capability with the realistic demands of a household.