Residential Building Inspector B1Wall Construction and Wall CoveringsMedium
An inspector observes a solid masonry wall constructed with 8-inch nominal concrete masonry units (CMU). What is the minimum nominal thickness of the solid masonry required for a foundation wall supporting a single-story residential building with a maximum unsupported height of 8 feet?
- A10 inches
- B12 inches
- C8 inches
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 8 inches
According to IRC Table R404.1.2(1) for masonry foundation walls, a solid masonry wall supporting a single-story building with an 8-foot unsupported height requires a minimum nominal thickness of 8 inches.
Why the other options are wrong
- A. 10-inch masonry would exceed the minimum requirement for this scenario and is typically used for taller walls or heavier loads.
- B. 12-inch masonry is required for greater unsupported heights or multiple stories, exceeding the minimum for this case.
- D. 6-inch masonry is generally not permitted for foundation walls unless specific engineered designs or very limited conditions apply.
Masonry Foundation Wall Thickness
The minimum nominal thickness of a masonry foundation wall depends on the number of stories supported and the unsupported height of the wall.
- 8-inch nominal thickness for 1-story with 8-foot unsupported height.
- 10-inch nominal thickness for 1-story with 9-foot unsupported height.
- 12-inch nominal thickness for 2-story with 8-foot unsupported height.
Memory trick: Foundation walls need to be thick enough to hold up the house, based on height and stories.