Residential Building Inspector B1Footings and FoundationsHard
A residential building inspector is reviewing the plans for a new single-family dwelling. The plans indicate a masonry foundation wall constructed from solid masonry units. According to the 2021 IRC, what is the minimum nominal thickness required for an unreinforced solid masonry foundation wall supporting a wall with a maximum height of 8 feet, measured from the top of the footing to the top of the foundation wall?
- A8 inches
- B12 inches
- C6 inches
- D10 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 8 inches
According to IRC Table R404.1.2(1), for unreinforced solid masonry foundation walls, a nominal thickness of 8 inches is permitted for a maximum height of 8 feet and a maximum backfill height of 7 feet. If the backfill height exceeds 7 feet, or the wall height exceeds 8 feet, a greater thickness or reinforcement would be required.
Why the other options are wrong
- B. Incorrect. While 12 inches would be acceptable, it is not the minimum required for this specific height.
- C. Incorrect. A 6-inch unreinforced solid masonry foundation wall is generally not permitted for an 8-foot height in the IRC.
- D. Incorrect. While 10 inches would be acceptable, it is not the minimum required for this specific height.
Unreinforced Solid Masonry Foundation Wall Thickness
The minimum nominal thickness required for an unreinforced foundation wall built from solid masonry units, based on its height and backfill conditions, as specified in the IRC.
- IRC Table R404.1.2(1) governs these requirements.
- Thickness depends on wall height and unbalanced backfill height.
- Ensures structural stability against lateral earth pressure and vertical loads.
- Unreinforced walls have stricter thickness limitations.
Memory trick: Unreinforced masonry needs 8 inches for 8 feet, like a double-8 bowling ball.