ICC Residential Plumbing Inspector
Exam (P1) Practice Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. Which of the following is the minimum slope for a 3-inch horizontal
building drain?
A. 1/4 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Rationale: According to the International Residential Code (IRC), a 3-
inch horizontal building drain must have a minimum slope of 1/4 inch
per foot to ensure proper drainage.
,2. What is the maximum distance a fixture trap can be located from the
vent for a 1-1/4 inch trap?
A. 2 feet
B. 3 feet
C. 4 feet
D. 5 feet
Rationale: IRC Table P3103.2 specifies that a 1-1/4 inch trap may be
located up to 5 feet from its vent.
3. Which material is approved for use in residential water distribution
systems?
A. Galvanized steel
B. Cross-linked polyethylene (PEX)
C. Asbestos-cement
D. Cast iron
Rationale: PEX is approved for potable water systems in residential
construction due to its flexibility, corrosion resistance, and durability.
4. What is the required minimum size of a residential water service line
for a one-family dwelling?
A. 3/4 inch
B. 1 inch
C. 1 inch
D. 1-1/4 inch
, Rationale: IRC P2903.5 requires a minimum 1-inch water service line
for a one-family dwelling to ensure adequate flow.
5. A water closet in a residential dwelling must have a minimum trap size
of:
A. 1-1/4 inch
B. 3 inches
C. 2 inches
D. 4 inches
Rationale: IRC P3109.1 specifies that the minimum trap size for a
water closet is 3 inches to prevent clogging and ensure proper
drainage.
6. What is the minimum vent size for a 1-1/2 inch fixture drain?
A. 1 inch
B. 1-1/4 inch
C. 1-1/2 inch
D. 2 inches
Rationale: IRC P3107.1 requires a minimum vent size of 1-1/4 inch for
a 1-1/2 inch fixture drain.
7. Which of the following is an acceptable method for testing a newly
installed DWV system in a residential dwelling?
A. Smoke test only
B. Water test or air test
C. Pressure test with potable water only
, D. Visual inspection only
Rationale: IRC P2503 allows for water or air testing to verify the
integrity of the drainage, waste, and vent system.
8. The minimum distance a vent can be from a trap for a 2-inch trap is:
A. 4 feet
B. 5 feet
C. 6 feet
D. 8 feet
Rationale: Per IRC Table P3103.2, a 2-inch trap may be vented up to 8
feet from the vent connection.
9. What is the maximum length of a clothes washer drain trap arm?
A. 2 feet
B. 3 feet
C. 4 feet
D. 5 feet
Rationale: IRC P317.3 specifies a maximum 4-foot trap arm for a
clothes washer to prevent siphoning and ensure proper venting.
10. Which type of pipe is prohibited for use as a water distribution
pipe in a residential dwelling?
A. Polybutylene (PB)
B. Copper Type L
C. CPVC
D. PEX
Exam (P1) Practice Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. Which of the following is the minimum slope for a 3-inch horizontal
building drain?
A. 1/4 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Rationale: According to the International Residential Code (IRC), a 3-
inch horizontal building drain must have a minimum slope of 1/4 inch
per foot to ensure proper drainage.
,2. What is the maximum distance a fixture trap can be located from the
vent for a 1-1/4 inch trap?
A. 2 feet
B. 3 feet
C. 4 feet
D. 5 feet
Rationale: IRC Table P3103.2 specifies that a 1-1/4 inch trap may be
located up to 5 feet from its vent.
3. Which material is approved for use in residential water distribution
systems?
A. Galvanized steel
B. Cross-linked polyethylene (PEX)
C. Asbestos-cement
D. Cast iron
Rationale: PEX is approved for potable water systems in residential
construction due to its flexibility, corrosion resistance, and durability.
4. What is the required minimum size of a residential water service line
for a one-family dwelling?
A. 3/4 inch
B. 1 inch
C. 1 inch
D. 1-1/4 inch
, Rationale: IRC P2903.5 requires a minimum 1-inch water service line
for a one-family dwelling to ensure adequate flow.
5. A water closet in a residential dwelling must have a minimum trap size
of:
A. 1-1/4 inch
B. 3 inches
C. 2 inches
D. 4 inches
Rationale: IRC P3109.1 specifies that the minimum trap size for a
water closet is 3 inches to prevent clogging and ensure proper
drainage.
6. What is the minimum vent size for a 1-1/2 inch fixture drain?
A. 1 inch
B. 1-1/4 inch
C. 1-1/2 inch
D. 2 inches
Rationale: IRC P3107.1 requires a minimum vent size of 1-1/4 inch for
a 1-1/2 inch fixture drain.
7. Which of the following is an acceptable method for testing a newly
installed DWV system in a residential dwelling?
A. Smoke test only
B. Water test or air test
C. Pressure test with potable water only
, D. Visual inspection only
Rationale: IRC P2503 allows for water or air testing to verify the
integrity of the drainage, waste, and vent system.
8. The minimum distance a vent can be from a trap for a 2-inch trap is:
A. 4 feet
B. 5 feet
C. 6 feet
D. 8 feet
Rationale: Per IRC Table P3103.2, a 2-inch trap may be vented up to 8
feet from the vent connection.
9. What is the maximum length of a clothes washer drain trap arm?
A. 2 feet
B. 3 feet
C. 4 feet
D. 5 feet
Rationale: IRC P317.3 specifies a maximum 4-foot trap arm for a
clothes washer to prevent siphoning and ensure proper venting.
10. Which type of pipe is prohibited for use as a water distribution
pipe in a residential dwelling?
A. Polybutylene (PB)
B. Copper Type L
C. CPVC
D. PEX
