A commercial building inspector is reviewing the design for a continuous concrete footing supporting a 10-inch thick masonry foundation wall. The design indicates a footing width of 20 inches. What is the minimum required thickness for this footing, according to the IBC?
- A10 inches
- B6 inches
- C8 inches
- D12 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 10 inches
According to IBC Section 1809.4, the thickness of concrete footings shall not be less than 6 inches. Additionally, the footing thickness must not be less than the projection of the footing from the face of the wall. With a 10-inch wall on a 20-inch footing, the projection is (20-10)/2 = 5 inches. However, the thickness must also not be less than the wall thickness, which is 10 inches in this case. Therefore, the minimum required footing thickness is 10 inches.
Why the other options are wrong
- B. 6 inches is the absolute minimum for any footing, but this specific scenario requires a greater thickness.
- C. 8 inches is less than the wall thickness and does not meet the projection or wall thickness requirement in this case.
- D. 12 inches would be acceptable, but it is not the minimum required thickness according to the code.
Footing Thickness (IBC)
The minimum thickness of a concrete footing is governed by IBC Section 1809.4, requiring it to be at least 6 inches, and not less than the projection of the footing beyond the foundation wall, nor less than the foundation wall thickness itself.
- Minimum 6 inches for all footings.
- Must be at least the footing projection beyond the wall.
- Must be at least the thickness of the foundation wall it supports.
Memory trick: Think 'Six, Project, Wall' for footing thickness rules.