Residential Building Inspector B1Footings and FoundationsHard
An inspector is evaluating a foundation wall made of unreinforced concrete. The wall is 8 feet high and the retained earth height is 7 feet. According to the 2021 IRC, what is the MINIMUM required thickness for this unreinforced concrete foundation wall, assuming a prescriptive design and average soil conditions?
- A12 inches
- B16 inches
- C10 inches
- D8 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 12 inches
According to IRC Table R404.1.2(1) for unreinforced concrete foundation walls supporting a wood frame wall, for an 8-foot total wall height and 7-foot retained earth height, the minimum required thickness is 12 inches. The table provides prescriptive requirements based on wall height, backfill height, and soil conditions.
Why the other options are wrong
- B. 16 inches would be acceptable but is not the minimum required.
- C. 10 inches is also typically insufficient for unreinforced concrete walls of this height and retained earth.
- D. 8 inches is typically insufficient for unreinforced concrete walls of this height and retained earth.
Unreinforced Concrete Foundation Wall Thickness
The minimum thickness for unreinforced concrete foundation walls is prescriptively determined by the IRC based on the wall's height, the height of retained earth, and soil conditions.
- IRC Table R404.1.2(1) provides prescriptive values.
- Unreinforced concrete requires greater thickness than reinforced.
- Retained earth height is a critical factor due to lateral pressure.
Memory trick: No steel, so thicker wall, must stand tall.