Residential Building Inspector B1Footings and FoundationsMedium
An inspector observes a foundation wall constructed from unreinforced concrete. The wall is 8 feet high and has an unbalanced backfill height of 6 feet. According to the 2021 IRC, what is the minimum thickness required for this unreinforced concrete foundation wall?
- A10 inches
- B6 inches
- C12 inches
- D8 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 8 inches
According to IRC Table R404.1.3(1) for unreinforced concrete foundation walls, for a wall height of 8 feet and an unbalanced backfill height of 6 feet, the minimum thickness required is 8 inches.
Why the other options are wrong
- A. Incorrect. While 10 inches would be acceptable, it is not the minimum required for this specific height and backfill condition.
- B. Incorrect. A 6-inch unreinforced concrete foundation wall is only permitted for shorter wall and backfill heights, such as 4 feet total height and 4 feet backfill.
- C. Incorrect. While 12 inches would be acceptable, it is not the minimum required for this specific height and backfill condition.
Unreinforced Concrete Foundation Wall Thickness
The minimum thickness required for a concrete foundation wall that does not contain reinforcing steel, based on its height and the height of unbalanced backfill.
- Regulated by IRC Table R404.1.3(1).
- Thickness increases with wall height and backfill height.
- Ensures structural stability against lateral earth pressure and vertical loads.
- Unreinforced walls have specific limitations to prevent failure.
Memory trick: Unreinforced concrete walls, for 8 feet high with 6 feet of dirt, need an 8-inch solid stance.