IPC - International Plumbing Code Sanitary Drainage Systems 2 — Questions and Answers
Question 1: A plumber is installing a 6-inch horizontal building drain for a multi-story residential building. According to IPC Table 704.1, what is the minimum slope required for this pipe?
- 1/4 inch per foot
- 3/16 inch per foot
- 1/8 inch per foot (Correct answer)
- 1/16 inch per foot
Correct answer: 1/8 inch per foot
IPC Table 704.1 specifies that horizontal drainage pipes 4 inches and larger in diameter require a minimum slope of 1/8 inch per foot. The steeper 1/4 inch per foot minimum applies only to pipes 3 inches and smaller in diameter.
Question 2: An inspector reviewing a commercial plumbing installation finds that a sanitary tee fitting has been used to make a horizontal-to-horizontal change in direction in a drainage line. According to IPC Section 706.3, how should this be treated?
- It is acceptable provided the branch is the same diameter as the main
- It is acceptable if a cleanout is installed immediately downstream
- It is prohibited because sanitary tees cannot be used for horizontal-to-horizontal changes in direction (Correct answer)
- It is acceptable only when the pipe is 3 inches or smaller in diameter
Correct answer: It is prohibited because sanitary tees cannot be used for horizontal-to-horizontal changes in direction
IPC Section 706.3 prohibits sanitary tees (and single sanitary tees used back-to-back) from being used as a change-in-direction fitting in a horizontal drainage application. These fittings are designed for vertical-to-horizontal transitions, not horizontal branch connections, because they do not provide the proper sweep needed for self-scouring flow.
Question 3: A trap is being installed under a lavatory in a commercial restroom. According to IPC Section 1002.3, what are the minimum and maximum allowable trap seal depths?
- 1 inch minimum and 3 inches maximum
- 2 inches minimum and 4 inches maximum (Correct answer)
- 1.5 inches minimum and 3.5 inches maximum
- 2 inches minimum and 6 inches maximum
Correct answer: 2 inches minimum and 4 inches maximum
IPC Section 1002.3 requires that the depth of a trap seal be not less than 2 inches and not more than 4 inches. A seal shallower than 2 inches is too easily lost to evaporation or siphonage, while one deeper than 4 inches can allow solids to accumulate and clog the trap.
Question 4: Under IPC Section 708.3.4, a cleanout is required at the base of each soil and waste stack. Which of the following also satisfies this requirement?
- A relief vent installed within 10 pipe diameters of the stack base
- A cleanout installed in the horizontal branch serving the stack within 2 feet of the base
- A wye fitting with removable plug installed at the point where the stack transitions to horizontal (Correct answer)
- Either a wye cleanout at the stack base or a cleanout on the horizontal drain within 10 feet of the base
Correct answer: A wye fitting with removable plug installed at the point where the stack transitions to horizontal
IPC Section 708.3.4 requires a cleanout at or near the base of each stack. A wye fitting with a removable plug at the transition from vertical to horizontal is the standard method used to satisfy this requirement, providing direct access to clear blockages that accumulate at this high-stress location in the system.
Question 5: A building drain serving a large office complex is 6 inches in diameter. When the contractor connects this drain to the public sewer at the property line, what does IPC Section 701.2 require regarding the size of the building sewer?
- The building sewer may be reduced one pipe size smaller than the building drain to increase velocity
- The building sewer must be the same size as or larger than the building drain it serves (Correct answer)
- The building sewer size is set exclusively by the public utility regardless of building drain size
- The building sewer must be a minimum of 8 inches in all commercial applications
Correct answer: The building sewer must be the same size as or larger than the building drain it serves
IPC Section 701.2 requires that the building sewer not be smaller in diameter than the building drain it serves. Reducing the sewer pipe would create a constriction that could cause backups, so the code mandates that the sewer maintain at least the same capacity as the building drain.
Question 6: An air admittance valve (AAV) is being installed on an individual fixture vent in a bathroom addition. According to IPC Section 918.3, which of the following represents a correct installation requirement for this device?
- The AAV must be installed below the flood level rim of the highest fixture it serves
- The AAV must be installed a minimum of 4 inches above the horizontal branch drain or fixture drain and must remain accessible (Correct answer)
- The AAV may be used as the sole means of venting for the entire building drainage stack
- The AAV must be sealed in an airtight enclosure to prevent sewer gas from escaping into the space
Correct answer: The AAV must be installed a minimum of 4 inches above the horizontal branch drain or fixture drain and must remain accessible
IPC Section 918.3 requires that an individual AAV be located a minimum of 4 inches above the horizontal branch drain or fixture drain it serves and that it remain accessible for inspection and maintenance. AAVs are one-way valves that admit air to prevent siphonage but must be above the drain to function correctly and must never be permanently enclosed.
IPC - International Plumbing Code Sanitary Drainage Systems 2
A plumber is installing a 6-inch horizontal building drain for a multi-story residential building.
According to IPC Table 704.1, what is the minimum slope required for this pipe?