Commercial Building Inspector B2Footings and FoundationsEasy
A geotechnical report for a new commercial building indicates the presence of bedrock at a depth of 6 feet. The building's design calls for spread footings. According to the IBC, what is the minimum embedment depth required for footings on bedrock, assuming the bedrock is sound and undisturbed?
- A6 inches
- B18 inches
- C24 inches
- D12 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 12 inches
IBC Section 1809.4 requires that all foundations, regardless of the type of construction, extend a minimum of 12 inches below the undisturbed ground surface. This applies to footings bearing on sound bedrock as well, ensuring adequate embedment and protection.
Why the other options are wrong
- A. This depth is insufficient for general foundation embedment requirements.
- B. While common for frost protection, it's not the minimum for embedment on bedrock in general.
- C. This depth is more than the minimum required by code for general embedment.
Footing Embedment on Bedrock
Minimum depth a footing must extend into sound, undisturbed bedrock, as per code, for stability and bearing.
- 12 inches minimum embedment.
- Ensures proper bearing and prevents erosion/undermining.
- Applies even if bedrock is shallow.
Memory trick: Even solid rock needs a foot of cover, for a foundation that won't hover.