CSLB General Building (B)Site Work, Foundations and ConcreteEasy
A contractor is finishing grading around a newly completed foundation. Per standard California building code requirements, the finish grade adjacent to the foundation must slope away from the structure at a minimum rate of:
- A5 percent for the first 10 feet
- B2 percent for the first 5 feet
- C1 percent for the first 20 feet
- D10 percent for the first 2 feet
Show answer & explanationAnswer & explanation
Correct answer: A. 5 percent for the first 10 feet
The California Building Code (based on the IBC/IRC) requires the ground immediately adjacent to the foundation to slope away at a minimum of 5 percent, equal to about 6 inches of fall over the first 10 feet, to direct surface water away from the structure and reduce moisture damage to the foundation.
Why the other options are wrong
- B. 2 percent over 5 feet does not provide the required minimum fall away from the foundation.
- C. 1 percent over 20 feet is far too shallow a slope to meet code drainage requirements.
- D. 10 percent over only 2 feet is steeper than required and not the standard code minimum.
Foundation Drainage Grading
Code requirement that finish grade slope away from a building foundation at a minimum of 5 percent (6 inches of fall) over the first 10 feet to direct water away from the structure.
- Minimum slope is 5 percent for first 10 feet
- Equivalent to about 6 inches of fall over 10 feet
- Purpose is to prevent water pooling against foundation
Memory trick: 'Six inches in ten feet keeps the foundation neat' — remember the 5% rule.