IRC Building Code Questions with correct
Answers 2023
Course
IRC
1. What is the minimum ceiling height for habitable spaces in residential buildings?
Answer: 7 feet (2134 mm).
Rationale: Per IRC Section R305.1, habitable spaces must have a minimum ceiling height of 7
feet to provide adequate headroom and comfort for occupants. Exceptions exist for basements
and certain sloped ceilings.
2. What is the maximum riser height for residential stairs?
Answer: 7 ¾ inches (196 mm).
Rationale: According to IRC Section R311.7.5.1, the maximum riser height is set to ensure safety
and uniformity in stair design. Uneven or excessively tall risers increase the risk of trips and falls.
3. How wide must stairways in residential buildings be at a minimum?
Answer: 36 inches (914 mm).
Rationale: Per IRC Section R311.7.1, stairways must have a minimum width of 36 inches to
ensure safe passage for occupants, especially during emergencies.
4. What is the minimum slope required for drainage on a residential roof?
Answer: 2% (¼ inch per foot).
Rationale: IRC Section R903.4 requires proper roof drainage to prevent water pooling, which
can lead to structural damage and leaks. This minimum slope ensures water is directed off the
roof.
5. What is the required minimum distance of untreated wood framing from the ground?
Answer: 6 inches.
Rationale: Per IRC Section R317.1, untreated wood must be at least 6 inches above the ground
to prevent moisture absorption and decay caused by contact with soil.
,6. How far must smoke alarms be installed from cooking appliances?
Answer: At least 10 feet (3 meters).
Rationale: IRC Section R314.3.3 states this distance minimizes false alarms triggered by cooking
smoke or steam while ensuring effective detection in the event of a fire.
7. What is the minimum required size for egress windows in a bedroom?
Answer:
Minimum opening height: 24 inches.
Minimum opening width: 20 inches.
Minimum net clear opening: 5.7 square feet (5.0 square feet for grade-level windows).
Rationale: Per IRC Section R310.2.1, these dimensions ensure a safe and accessible
means of escape in emergencies.
8. What is the required fire-resistance rating for a wall between an attached garage and a
residence?
Answer: 1/2-inch gypsum board.
Rationale: IRC Section R302.6 requires this fire-resistance rating to delay the spread of fire from
the garage to the living space, allowing occupants time to evacuate.
9. What is the maximum distance between balusters on a residential guardrail?
Answer: 4 inches (102 mm).
Rationale: IRC Section R312.1.3 mandates that balusters must be spaced so a 4-inch sphere
cannot pass through, to prevent children from falling through gaps.
10. What is the minimum height for handrails on residential stairways?
Answer: 34 inches to 38 inches (measured from the nosing of treads).
Rationale: Per IRC Section R311.7.8.1, this range provides adequate support for most users
while ensuring the handrail is neither too low nor too high for effective use.
11. What is the maximum allowable spacing between deck joists for a deck with 5/4-inch
thick wood planks?
,Answer: 16 inches on center.
Rationale: IRC Section R507.7 requires deck joist spacing to ensure adequate structural support
for typical loads. Wider spacing can cause excessive deflection or sagging of deck boards.
12. What is the minimum height of a guardrail for a deck more than 30 inches above grade?
Answer: 36 inches.
Rationale: Per IRC Section R312.1.2, guardrails must be at least 36 inches high to prevent falls
from elevated surfaces.
13. What is the minimum width required for an egress door in a residential dwelling?
Answer: 32 inches (clear width).
Rationale: IRC Section R311.2 specifies this minimum width to ensure adequate space for
occupants to exit safely during emergencies.
14. What is the required fire separation distance between two residential buildings on the
same lot?
Answer: 6 feet.
Rationale: Per IRC Table R302.1(1), this separation prevents the spread of fire between
buildings and protects both structures.
15. What is the minimum thickness for a concrete slab-on-ground floor in a residential
building?
Answer: 3.5 inches.
Rationale: IRC Section R506.1 establishes this minimum thickness to provide adequate strength
and durability for residential floors.
16. How far must a wood-burning stove be located from combustible materials?
Answer: At least 36 inches unless otherwise specified by the manufacturer.
Rationale: IRC Section M1410.2 ensures that the stove is far enough away from combustible
materials to prevent fires caused by radiant heat.
, 17. What is the required slope for a building sewer?
Answer: 1/4 inch per foot (2% slope).
Rationale: Per IRC Section P3005.3, this slope ensures adequate flow of wastewater to the
sewer system, reducing the risk of blockages.
18. What is the minimum height of a chimney above a roof?
Answer: 3 feet above the roof and 2 feet higher than any part of the roof within 10 feet.
Rationale: IRC Section R1003.9 ensures proper draft and prevents smoke and combustion gases
from re-entering the home.
19. What is the minimum distance between a septic tank and a residential well?
Answer: 50 feet.
Rationale: IRC Section P2609.2 prevents contamination of drinking water sources from
wastewater.
20. What is the minimum width required for hallways in a residential building?
Answer: 36 inches.
Rationale: Per IRC Section R311.6, this width provides adequate space for safe passage and
accessibility.
21. What is the minimum pressure rating for water supply piping in a residential building?
Answer: 100 psi at 180°F.
Rationale: IRC Section P2906.4 specifies this requirement to ensure piping can withstand typical
residential water pressure and temperature conditions.
22. What is the maximum allowable air gap for a plumbing fixture?
Answer: Twice the diameter of the fixture drain.
Rationale: IRC Section P2902.3 ensures that there is no backflow of contaminated water into
the potable water supply.
Answers 2023
Course
IRC
1. What is the minimum ceiling height for habitable spaces in residential buildings?
Answer: 7 feet (2134 mm).
Rationale: Per IRC Section R305.1, habitable spaces must have a minimum ceiling height of 7
feet to provide adequate headroom and comfort for occupants. Exceptions exist for basements
and certain sloped ceilings.
2. What is the maximum riser height for residential stairs?
Answer: 7 ¾ inches (196 mm).
Rationale: According to IRC Section R311.7.5.1, the maximum riser height is set to ensure safety
and uniformity in stair design. Uneven or excessively tall risers increase the risk of trips and falls.
3. How wide must stairways in residential buildings be at a minimum?
Answer: 36 inches (914 mm).
Rationale: Per IRC Section R311.7.1, stairways must have a minimum width of 36 inches to
ensure safe passage for occupants, especially during emergencies.
4. What is the minimum slope required for drainage on a residential roof?
Answer: 2% (¼ inch per foot).
Rationale: IRC Section R903.4 requires proper roof drainage to prevent water pooling, which
can lead to structural damage and leaks. This minimum slope ensures water is directed off the
roof.
5. What is the required minimum distance of untreated wood framing from the ground?
Answer: 6 inches.
Rationale: Per IRC Section R317.1, untreated wood must be at least 6 inches above the ground
to prevent moisture absorption and decay caused by contact with soil.
,6. How far must smoke alarms be installed from cooking appliances?
Answer: At least 10 feet (3 meters).
Rationale: IRC Section R314.3.3 states this distance minimizes false alarms triggered by cooking
smoke or steam while ensuring effective detection in the event of a fire.
7. What is the minimum required size for egress windows in a bedroom?
Answer:
Minimum opening height: 24 inches.
Minimum opening width: 20 inches.
Minimum net clear opening: 5.7 square feet (5.0 square feet for grade-level windows).
Rationale: Per IRC Section R310.2.1, these dimensions ensure a safe and accessible
means of escape in emergencies.
8. What is the required fire-resistance rating for a wall between an attached garage and a
residence?
Answer: 1/2-inch gypsum board.
Rationale: IRC Section R302.6 requires this fire-resistance rating to delay the spread of fire from
the garage to the living space, allowing occupants time to evacuate.
9. What is the maximum distance between balusters on a residential guardrail?
Answer: 4 inches (102 mm).
Rationale: IRC Section R312.1.3 mandates that balusters must be spaced so a 4-inch sphere
cannot pass through, to prevent children from falling through gaps.
10. What is the minimum height for handrails on residential stairways?
Answer: 34 inches to 38 inches (measured from the nosing of treads).
Rationale: Per IRC Section R311.7.8.1, this range provides adequate support for most users
while ensuring the handrail is neither too low nor too high for effective use.
11. What is the maximum allowable spacing between deck joists for a deck with 5/4-inch
thick wood planks?
,Answer: 16 inches on center.
Rationale: IRC Section R507.7 requires deck joist spacing to ensure adequate structural support
for typical loads. Wider spacing can cause excessive deflection or sagging of deck boards.
12. What is the minimum height of a guardrail for a deck more than 30 inches above grade?
Answer: 36 inches.
Rationale: Per IRC Section R312.1.2, guardrails must be at least 36 inches high to prevent falls
from elevated surfaces.
13. What is the minimum width required for an egress door in a residential dwelling?
Answer: 32 inches (clear width).
Rationale: IRC Section R311.2 specifies this minimum width to ensure adequate space for
occupants to exit safely during emergencies.
14. What is the required fire separation distance between two residential buildings on the
same lot?
Answer: 6 feet.
Rationale: Per IRC Table R302.1(1), this separation prevents the spread of fire between
buildings and protects both structures.
15. What is the minimum thickness for a concrete slab-on-ground floor in a residential
building?
Answer: 3.5 inches.
Rationale: IRC Section R506.1 establishes this minimum thickness to provide adequate strength
and durability for residential floors.
16. How far must a wood-burning stove be located from combustible materials?
Answer: At least 36 inches unless otherwise specified by the manufacturer.
Rationale: IRC Section M1410.2 ensures that the stove is far enough away from combustible
materials to prevent fires caused by radiant heat.
, 17. What is the required slope for a building sewer?
Answer: 1/4 inch per foot (2% slope).
Rationale: Per IRC Section P3005.3, this slope ensures adequate flow of wastewater to the
sewer system, reducing the risk of blockages.
18. What is the minimum height of a chimney above a roof?
Answer: 3 feet above the roof and 2 feet higher than any part of the roof within 10 feet.
Rationale: IRC Section R1003.9 ensures proper draft and prevents smoke and combustion gases
from re-entering the home.
19. What is the minimum distance between a septic tank and a residential well?
Answer: 50 feet.
Rationale: IRC Section P2609.2 prevents contamination of drinking water sources from
wastewater.
20. What is the minimum width required for hallways in a residential building?
Answer: 36 inches.
Rationale: Per IRC Section R311.6, this width provides adequate space for safe passage and
accessibility.
21. What is the minimum pressure rating for water supply piping in a residential building?
Answer: 100 psi at 180°F.
Rationale: IRC Section P2906.4 specifies this requirement to ensure piping can withstand typical
residential water pressure and temperature conditions.
22. What is the maximum allowable air gap for a plumbing fixture?
Answer: Twice the diameter of the fixture drain.
Rationale: IRC Section P2902.3 ensures that there is no backflow of contaminated water into
the potable water supply.
