CRC Foundation & Structural Systems 1 — Questions and Answers
Question 1: According to the IRC, what is the minimum footing width for a one-story wood-frame structure built on soil with a load-bearing capacity of 1,500 psf?
- 12 inches (Correct answer)
- 16 inches
- 20 inches
- 24 inches
Correct answer: 12 inches
IRC Table R403.1 specifies a minimum footing width of 12 inches for a one-story structure on soil with a 1,500 psf bearing capacity.
Question 2: What is the primary purpose of installing a vapor barrier beneath a concrete slab-on-grade in residential construction?
- To prevent frost heave under the slab
- To reduce moisture migration from the soil up into the slab (Correct answer)
- To serve as a thermal insulator
- To prevent shrinkage cracking during curing
Correct answer: To reduce moisture migration from the soil up into the slab
A vapor barrier (retarder) prevents soil moisture from wicking upward through capillary action into the concrete slab and living spaces above.
Question 3: Per the IRC, what is the minimum concrete compressive strength (f'c) required for a residential garage floor slab?
- 2,500 psi
- 3,000 psi
- 3,500 psi (Correct answer)
- 4,000 psi
Correct answer: 3,500 psi
IRC Table R402.2 requires a minimum f'c of 3,500 psi for garage floor slabs and other concrete exposed to freezing, thawing, or deicers.
Question 4: What is the primary structural function of anchor bolts installed in a residential concrete foundation?
- To reinforce the concrete footing against lateral soil pressure
- To mechanically connect the sill plate to the foundation wall (Correct answer)
- To provide a drainage pathway through the foundation
- To prevent differential settlement of the footing
Correct answer: To mechanically connect the sill plate to the foundation wall
Anchor bolts fasten the wood sill plate to the concrete or masonry foundation, transferring lateral forces (wind, seismic) from the structure to the foundation.
Question 5: Which foundation type is most appropriate when constructing a residential structure on significantly sloped terrain to maintain required frost-depth embedment?
- Floating slab-on-grade
- Full basement with uniform depth
- Stepped footings that follow the grade change (Correct answer)
- Pile foundation with grade beams
Correct answer: Stepped footings that follow the grade change
Stepped footings allow the footing depth to remain constant relative to the slope while maintaining required frost-depth embedment at each level.
Question 6: What is the minimum embedment depth for anchor bolts set in concrete foundation walls per the IRC?
- 5 inches
- 7 inches (Correct answer)
- 9 inches
- 12 inches
Correct answer: 7 inches
IRC Section R403.1.6 requires anchor bolts to have a minimum embedment depth of 7 inches into concrete or masonry.
Question 7: What is the minimum clearance required between the bottom of floor joists and the ground surface in a residential crawl space per the IRC?
- 12 inches
- 18 inches (Correct answer)
- 24 inches
- 36 inches
Correct answer: 18 inches
IRC Section R408.4 requires a minimum clearance of 18 inches between the ground and the bottom of wood floor joists to prevent moisture damage and allow inspection.
CRC Foundation & Structural Systems 1
According to the IRC, what is the minimum footing width for a one-story wood-frame structure built on soil with a load-bearing capacity of 1,500 psf?