InterNACHI Plumbing Systems Inspection 4 — Questions and Answers
Question 1: What is the minimum distance a plumbing vent must extend above a flat roof where the roof is used as a deck or occupied space?
- 6 inches
- 12 inches
- 24 inches
- 7 feet (Correct answer)
Correct answer: 7 feet
When a roof is used as a deck or occupied area, vents must extend at least 7 feet above the roof surface to keep sewer gases away from occupants.
Question 2: Which of the following is a sign of a failing supply stop valve under a sink?
- Low hot water pressure only
- Mineral deposits or corrosion around the valve packing nut (Correct answer)
- The faucet aerator is clogged
- The drain empties slowly
Correct answer: Mineral deposits or corrosion around the valve packing nut
Mineral deposits or corrosion around the packing nut of a stop valve indicate a slow leak or deteriorating stem seal that can worsen over time.
Question 3: A home inspector finds a water heater in a garage installed directly on the concrete floor. The concern with this installation is:
- Concrete floors cause accelerated tank corrosion
- The pilot light or burner ignition is too close to potential fuel vapors at floor level (Correct answer)
- The unit cannot be properly anchored on concrete
- Moisture from the slab will void the warranty
Correct answer: The pilot light or burner ignition is too close to potential fuel vapors at floor level
Gas water heaters must be elevated at least 18 inches in garages to keep ignition sources above the level where heavier-than-air fuel vapors may accumulate.
Question 4: What is the function of a pressure-reducing valve (PRV) in a residential plumbing system?
- It increases incoming street pressure for better flow
- It reduces high municipal water pressure to a safe level for household piping and fixtures (Correct answer)
- It prevents water from flowing backward into the supply main
- It regulates hot water temperature at the heater
Correct answer: It reduces high municipal water pressure to a safe level for household piping and fixtures
A PRV reduces high incoming water pressure (typically above 80 psi) to a safe, consistent pressure, protecting pipes, fixtures, and appliances.
Question 5: Which pipe material is identified by its distinctive orange color and is used for gas supply lines?
- CPVC
- CSST
- HDPE
- Corrugated stainless steel tubing with orange jacket (CSST) (Correct answer)
Correct answer: Corrugated stainless steel tubing with orange jacket (CSST)
CSST (corrugated stainless steel tubing) with an orange jacket is a flexible gas piping product; it must be properly bonded to mitigate lightning strike risks.
Question 6: During a home inspection, the inspector turns on multiple fixtures simultaneously and notices a dramatic drop in water pressure. This suggests:
- A faulty pressure-reducing valve
- Inadequate pipe size, a partially closed valve, or significant pipe corrosion restricting flow (Correct answer)
- The water meter is undersized
- Normal behavior in all homes
Correct answer: Inadequate pipe size, a partially closed valve, or significant pipe corrosion restricting flow
A significant pressure drop under simultaneous demand points to undersized supply piping, obstruction, or a partially closed main valve restricting flow.
Question 7: What does a 'dielectric union' prevent in a plumbing system?
- Backflow at fixture connections
- Galvanic corrosion where dissimilar metals are joined (Correct answer)
- Thermal expansion in water heater connections
- Sewer gas migration at pipe joints
Correct answer: Galvanic corrosion where dissimilar metals are joined
A dielectric union uses a plastic insulating sleeve to electrically isolate dissimilar metals (such as copper and steel), preventing galvanic corrosion at the joint.
InterNACHI Plumbing Systems Inspection 4
What is the minimum distance a plumbing vent must extend above a flat roof where the roof is used as a deck or occupied space?