Journeyman Plumber ExamPlumbing Code and RegulationsEasy
A plumber is inspecting a new commercial building's sanitary drainage system before the final inspection. All horizontal drainage piping must be installed with a minimum uniform slope to ensure proper gravity flow. What is the minimum required slope for a 3-inch (75 mm) horizontal drainage pipe?
- A1/8 inch per foot (1.04%)
- B1/4 inch per foot (2.08%)
- C1/2 inch per foot (4.17%)
- D1/16 inch per foot (0.52%)
Show answer & explanationAnswer & explanation
Correct answer: B. 1/4 inch per foot (2.08%)
According to both the UPC and IPC, horizontal drainage piping 2 1/2 inches or less in diameter requires a minimum slope of 1/4 inch per foot. For pipe diameters 3 inches to 6 inches, the minimum slope is also 1/4 inch per foot.
Why the other options are wrong
- A. 1/8 inch per foot is only permitted for horizontal drainage piping 8 inches or larger in diameter.
- C. 1/2 inch per foot is an acceptable slope but is not the minimum required for 3-inch pipe; it's often used for smaller branch drains.
- D. 1/16 inch per foot is insufficient for drainage piping and typically not allowed.
Drainage Pipe Minimum Slope
The least amount of downward inclination required for horizontal drainage piping to ensure self-scouring velocity and proper waste removal.
- Varies by pipe diameter (e.g., 1/4 inch/foot for smaller pipes).
- Ensures solids are carried away effectively.
- Critical for preventing blockages and maintaining hygiene.
Memory trick: Quarter Inch Per Foot, Makes Waste Scoot!