Residential Building Inspector B1Footings and FoundationsEasy
An inspector is checking the foundation drainage system for a new residential building. The foundation walls are constructed of concrete masonry units (CMU). According to the 2021 IRC, what is the MINIMUM required slope for the finished grade away from the foundation?
- A12 inches in 10 feet
- B1 inch in 10 feet
- C2 inches in 10 feet
- D6 inches in 10 feet
Show answer & explanationAnswer & explanation
Correct answer: D. 6 inches in 10 feet
IRC Section R401.3 requires that the finished grade shall slope a minimum of 6 inches in the first 10 feet away from the foundation. This ensures positive drainage and prevents water accumulation against the foundation.
Why the other options are wrong
- A. While more slope is generally better, this is not the minimum required and might be impractical in some cases.
- B. This slope is insufficient to provide adequate drainage.
- C. This slope is insufficient to provide adequate drainage.
Finished Grade Slope
The finished grade around a residential foundation must slope away from the building to ensure positive drainage and prevent water accumulation against the foundation walls.
- IRC R401.3 specifies minimum slope.
- Prevents hydrostatic pressure and moisture intrusion.
- Applies to the first 10 feet from the foundation.
Memory trick: Slope away, keep water at bay.