IPC Plumbing Fixtures and Fittings 3 — Questions and Answers
Question 1: According to the IPC, what minimum number of water closets must be provided for female occupants in an assembly occupancy with 150 women?
- 3
- 4
- 5 (Correct answer)
- 6
Correct answer: 5
Based on IPC Table 403.1, assembly occupancies require 1 water closet per 50 female occupants for the first 150, resulting in a minimum of 3, but the actual IPC table typically requires a higher ratio — 5 fixtures for 150 female occupants.
The IPC uses Table 403.1 to determine minimum plumbing fixture counts based on occupancy type and occupant load. For assembly occupancies, the water closet requirements for female occupants are more generous than for male occupants, reflecting typical usage patterns. The table specifies ratios that result in approximately 1 water closet per 25-30 female occupants for assembly spaces, yielding approximately 5 water closets for 150 female occupants. These minimum fixture counts ensure adequate facilities to prevent excessive wait times and maintain sanitary conditions in high-traffic public venues.
Question 2: What does the IPC specify about the drainage connection for a clothes washer standpipe?
- The standpipe must be at least 18 inches tall
- The standpipe must be between 18 and 42 inches above the trap weir (Correct answer)
- The standpipe must connect directly to the main drain without a trap
- Any height standpipe is acceptable
Correct answer: The standpipe must be between 18 and 42 inches above the trap weir
The IPC requires clothes washer standpipes to be between 18 and 42 inches above the trap weir to prevent both siphonage and overflow.
The IPC specifies that a clothes washer standpipe must extend between 18 and 42 inches above the trap weir. The minimum 18-inch height prevents the powerful discharge pump of a washing machine from siphoning the trap seal, which would allow sewer gases to enter the living space. The maximum 42-inch height ensures the pump can effectively discharge into the standpipe without excessive back pressure. The standpipe must be a minimum 2-inch diameter and connect to a proper P-trap. This specification is one of the most commonly tested IPC requirements and is frequently cited during residential plumbing inspections.
Question 3: Under the IPC, what type of valve is required on the water supply to each individual plumbing fixture?
- A pressure-reducing valve
- An accessible shutoff valve (Correct answer)
- A check valve
- No individual valve is required
Correct answer: An accessible shutoff valve
The IPC requires an accessible shutoff valve on the water supply to each individual plumbing fixture to allow isolation for maintenance or repair.
The IPC requires that each plumbing fixture be provided with an accessible shutoff valve on its water supply piping. This applies to both hot and cold water supplies. The shutoff valve allows the water supply to an individual fixture to be turned off for repairs, replacement, or maintenance without disrupting water service to other fixtures in the building. The valve must be accessible without requiring the removal of permanent building components. Common valve types used include quarter-turn ball valves and multi-turn compression valves. This requirement is fundamental to serviceable plumbing design.
Question 4: According to the IPC, what is the minimum trap size required for a residential kitchen sink?
- 1-1/4 inches
- 1-1/2 inches (Correct answer)
- 2 inches
- 3 inches
Correct answer: 1-1/2 inches
The IPC requires a minimum 1-1/2 inch trap for residential kitchen sinks.
The IPC specifies minimum trap sizes for each fixture type based on the fixture's drainage requirements. For residential kitchen sinks, the minimum trap size is 1-1/2 inches. This is larger than the 1-1/4 inch minimum for lavatories, reflecting the greater volume and variety of waste that kitchen sinks handle, including food particles and grease. For comparison, bathtubs also require a 1-1/2 inch minimum trap, while water closets have integral traps and floor drains typically require a 2-inch minimum trap. The trap size directly affects drainage performance and the fixture's resistance to clogging.
Question 5: What does the IPC require regarding drinking fountain installations in buildings?
- One fountain per floor is always sufficient
- The number required depends on occupancy type and occupant load (Correct answer)
- Drinking fountains are optional in all buildings
- Only buildings over 10,000 sq ft need fountains
Correct answer: The number required depends on occupancy type and occupant load
The IPC requires drinking fountains based on occupancy type and occupant load as specified in the minimum fixture count table.
The IPC mandates drinking fountain installations based on the building's occupancy classification and the number of occupants, as specified in Table 403.1. Different occupancy types have different ratios — for example, assembly and educational occupancies typically require 1 drinking fountain per 150 occupants, while business occupancies may require 1 per 100 occupants. The IPC also requires that where drinking fountains are provided, at least 50% must comply with accessibility requirements for people using wheelchairs, and at least 50% must be designed for standing persons. Bottle filler stations may be substituted for up to 50% of the required drinking fountains.
Question 6: Under the IPC, what is the maximum distance a fixture trap can be located from the fixture outlet?
- 12 inches
- 24 inches (Correct answer)
- 30 inches
- No limit if properly vented
Correct answer: 24 inches
The IPC limits the distance between a fixture outlet and its trap to a maximum of 24 inches to ensure proper drainage and trap seal maintenance.
The IPC specifies that the vertical distance between a fixture outlet and the trap weir shall not exceed 24 inches. This limitation ensures that the fixture drains efficiently and that the water seal in the trap is properly maintained. Excessive distance between the fixture and its trap can result in increased velocity of drainage water, which may cause siphonage of the trap seal. Additionally, the tailpiece between the fixture and trap should be as direct as possible, without unnecessary horizontal offsets. This distance requirement works in conjunction with vent location requirements to protect the trap seal from both siphonage and back-pressure.
IPC Plumbing Fixtures and Fittings 3
According to the IPC, what minimum number of water closets must be provided for female occupants in an assembly occupancy with 150 women?