Residential Building Inspector B1Wall Construction and Wall CoveringsMedium
An inspector is evaluating a residential garage wall constructed with concrete masonry units (CMU). The wall is 8 feet high and has a load-bearing condition. What is the minimum nominal wall thickness required for this single-story garage wall, assuming Type M or S mortar and a maximum f'm of 1,500 psi?
- A10 inches
- B8 inches
- C12 inches
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 8 inches
According to IRC Table R606.2.1(1) for plain concrete masonry walls, a single-story load-bearing wall with an 8-foot height requires a minimum nominal thickness of 8 inches, assuming Type M or S mortar and f'm of 1,500 psi.
Why the other options are wrong
- A. 10-inch nominal CMU walls would exceed the minimum requirement for this scenario and are typically used for taller walls or heavier loads.
- C. 12-inch nominal CMU walls are required for greater unsupported heights or multiple stories, exceeding the minimum for this case.
- D. 6-inch nominal CMU walls are generally not permitted for load-bearing applications in residential construction.
CMU Wall Thickness (Load-Bearing)
The minimum nominal thickness for load-bearing concrete masonry unit (CMU) walls depends on the number of stories supported and the wall's unsupported height.
- 8-inch nominal thickness for 1-story, 8-foot high walls.
- Increased thickness for taller walls or more stories.
- Mortar type and masonry compressive strength (f'm) are also factors.
Memory trick: CMU walls need the right thickness to stand tall and hold the weight, like a strong Lego tower.