306A Drainage and Venting Systems 2 — Questions and Answers
Question 1: What is the difference between a soil stack and a waste stack?
- Soil stacks are underground; waste stacks are above ground
- A soil stack carries water closet discharge; a waste stack does not (Correct answer)
- Soil stacks are vertical; waste stacks are horizontal
- There is no difference
Correct answer: A soil stack carries water closet discharge; a waste stack does not
A soil stack carries discharge from water closets (containing fecal matter), while a waste stack carries discharge from fixtures that do not include water closets, such as sinks, bathtubs, and showers.
Question 2: What is the purpose of a circuit vent in a multi-fixture drainage system?
- To vent each fixture individually
- To serve as a single vent connection for a group of fixtures on a horizontal branch (Correct answer)
- To replace the main vent stack
- To connect the drainage system to the building sewer
Correct answer: To serve as a single vent connection for a group of fixtures on a horizontal branch
A circuit vent serves a group of fixtures (typically up to 8) on a single horizontal branch by connecting between the two most upstream fixtures and rising to the vent stack, reducing the number of individual vent pipes needed.
Question 3: What is the maximum distance that a vent can run horizontally below the flood level rim of the fixture it serves?
- No horizontal vent is permitted below the flood level rim (Correct answer)
- 150 mm maximum
- 300 mm maximum
- Any distance if properly graded
Correct answer: No horizontal vent is permitted below the flood level rim
A vent pipe must not run horizontally below the flood level rim of the fixture it serves because waste water could flow into the vent during a backup condition, blocking the air passage.
Question 4: What is an 'island vent' (loop vent) used for?
- Venting fixtures on a rooftop
- Venting a kitchen sink in an island counter where a traditional vent cannot rise directly to the roof (Correct answer)
- Venting outdoor plumbing fixtures
- Replacing the main vent stack
Correct answer: Venting a kitchen sink in an island counter where a traditional vent cannot rise directly to the roof
An island vent (loop vent) is used when a sink is installed in a kitchen island, making it impossible to run a vent directly upward. The vent loops under the counter and connects to a vent pipe at the nearest wall before rising above the flood level rim.
Question 5: What must be done if a vent pipe is exposed to freezing conditions where it terminates through the roof?
- Insulate the pipe only
- Increase the vent size by at least one pipe diameter before it passes through the roof (Correct answer)
- Install a heat trace cable
- No special treatment is required
Correct answer: Increase the vent size by at least one pipe diameter before it passes through the roof
In cold climates, vent pipes must be increased by at least one pipe size before passing through the roof to prevent frost closure. Moisture-laden air from the drainage system can freeze and block a smaller vent opening.
Question 6: What is the purpose of a fresh air inlet (fresh air vent) in a building drainage system?
- To provide combustion air for gas appliances
- To introduce fresh air into the drainage system near the building trap to promote air circulation (Correct answer)
- To exhaust sewer gases above the roof
- To supply ventilation to the basement
Correct answer: To introduce fresh air into the drainage system near the building trap to promote air circulation
A fresh air inlet is installed on the building side of a building trap to allow fresh air to enter the drainage system, ensuring continuous air circulation and reducing the buildup of sewer gases.
306A Drainage and Venting Systems 2
What is the difference between a soil stack and a waste stack?