Residential Building Inspector B1Building Planning and Life SafetyMedium
A residential building inspector is conducting a framing inspection for a new single-family dwelling. The plans indicate the use of continuous concrete foundations. What is the minimum required thickness for a concrete foundation wall that supports a wood-frame wall?
- A8 inches
- B6 inches
- C4 inches
- D10 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 6 inches
According to the 2021 IRC, Table R404.1.2(1) Minimum Thickness of Foundation Walls (nominal), for concrete foundation walls supporting a wood-frame wall, the minimum nominal thickness is 6 inches (152 mm). This applies to plain concrete walls.
Why the other options are wrong
- A. 8 inches is a common thickness and may be required for taller walls or specific soil conditions, but not the minimum.
- C. 4 inches is generally too thin for a load-bearing foundation wall.
- D. 10 inches exceeds the minimum requirement for this scenario.
Concrete Foundation Wall Thickness
The minimum nominal thickness required for a concrete foundation wall, based on the type of material it supports and other factors.
- Provides structural support for the building superstructure.
- Thickness varies with wall height, soil conditions, and supported loads.
- Specified in IRC Table R404.1.2(1).
Memory trick: Foundation walls, six inches thick, support the house, strong and quick.