CSLB C-36 Plumbing ContractorPlanning and EstimatingHard
A plumbing contractor is reviewing blueprints for a new multi-family residential building. The plans indicate the use of a combination waste and vent system for certain areas. Which of the following conditions is a primary requirement for installing a combination waste and vent system according to the Uniform Plumbing Code (UPC)?
- AThe horizontal branch drain must be oversized in relation to its drainage fixture units (DFU).
- BThe building must be no more than two stories in height.
- CThe system must only serve floor drains and sinks.
- DEach fixture must be individually vented upstream of the trap.
Show answer & explanationAnswer & explanation
Correct answer: A. The horizontal branch drain must be oversized in relation to its drainage fixture units (DFU).
The UPC allows combination waste and vent systems under specific conditions, one of which is that the horizontal branch drain must be at least two pipe sizes larger than the minimum required for the drainage fixture units (DFU) it serves, to ensure adequate air circulation and prevent trap siphonage.
Why the other options are wrong
- B. Building height is not a direct primary condition for combination waste and vent systems; rather, it relates to overall system design and limitations.
- C. Combination systems can serve various fixtures, not just floor drains and sinks, though specific fixture types may have limitations.
- D. Combination systems are designed to eliminate the need for individual vents for each fixture, which is their primary advantage.
Combination Waste and Vent System (UPC)
A plumbing system design where the horizontal branch drain also serves as the vent for the fixtures connected to it, reducing the need for separate vent piping.
- Permitted under strict UPC conditions, often for specific fixture groups.
- Requires oversizing of the horizontal drain to ensure proper air circulation.
- Reduces material and labor costs compared to conventional venting.
Memory trick: Combo needs a bigger pipe to breathe.