NHIE Plumbing 2 — Questions and Answers
Question 1: What is the minimum slope required for a horizontal drain pipe of 3 inches or less in diameter?
- 1/8 inch per foot
- 1/4 inch per foot (Correct answer)
- 1/2 inch per foot
- 1 inch per foot
Correct answer: 1/4 inch per foot
Horizontal drain pipes 3 inches or less in diameter require a minimum slope of 1/4 inch per foot to ensure proper drainage.
Question 2: Which type of pipe is NOT approved for use as a drain, waste, and vent (DWV) pipe in most US jurisdictions?
- ABS plastic
- PVC plastic
- CPVC (Correct answer)
- Cast iron
Correct answer: CPVC
CPVC (chlorinated polyvinyl chloride) is approved for hot and cold water supply lines but is not approved for DWV applications.
Question 3: A home inspector observes a P-trap installed below the floor slab with no access. What is the primary concern?
- P-traps must always be chrome-plated
- The trap is inaccessible for cleaning and cannot be inspected for leaks (Correct answer)
- P-traps are prohibited below slabs
- The water seal will evaporate faster below a slab
Correct answer: The trap is inaccessible for cleaning and cannot be inspected for leaks
Traps installed below the floor slab must be accessible for cleaning and inspection; inaccessible traps are a deficiency.
Question 4: What does a water hammer arrestor prevent?
- Backflow of contaminated water into supply lines
- Pressure surges that cause banging pipes when valves close quickly (Correct answer)
- Sediment buildup in water heater tanks
- Freezing of supply pipes in cold climates
Correct answer: Pressure surges that cause banging pipes when valves close quickly
Water hammer arrestors absorb the pressure shock wave created when fast-closing valves suddenly stop water flow, preventing pipe banging.
Question 5: An inspector finds a vent pipe that terminates 6 inches above the roof surface. What should be noted?
- This is acceptable in all climates
- In cold climates, the termination should be at least 12 inches above the roof to prevent frost closure (Correct answer)
- Vent pipes must terminate at least 24 inches above the roof in all cases
- The vent pipe must be capped to prevent odors
Correct answer: In cold climates, the termination should be at least 12 inches above the roof to prevent frost closure
In climates subject to frost, vent pipe terminations should extend at least 12 inches above the roof to reduce risk of frost closure blocking the vent.
Question 6: Which condition would most likely cause a gurgling sound at a fixture when another nearby fixture is draining?
- Excessive water pressure at the supply line
- An undersized or blocked vent pipe causing siphoning of trap water seals (Correct answer)
- A worn faucet washer
- Galvanized pipe corrosion
Correct answer: An undersized or blocked vent pipe causing siphoning of trap water seals
Gurgling at one fixture while another drains indicates an inadequate vent, causing negative pressure that siphons the trap seal and allows sewer gases to enter.
Question 7: What is the purpose of a backwater valve installed in a drain line?
- To regulate hot and cold water mixing temperatures
- To prevent municipal sewer water from backing up into the home during flooding (Correct answer)
- To increase water pressure to upper floors
- To allow cleanout access for drain snaking
Correct answer: To prevent municipal sewer water from backing up into the home during flooding
A backwater valve (check valve) allows drain flow in one direction only, preventing sewage from backing up into the home when the municipal sewer is overwhelmed.
NHIE Plumbing 2
What is the minimum slope required for a horizontal drain pipe of 3 inches or less in diameter?