CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A landscape contractor is grading a site for a new lawn area. The design calls for a final grade that ensures water drains away from the residential foundation. What is the minimum recommended positive drainage slope for the finished grade adjacent to the foundation?
- A0.5% for the first 5 feet
- B3.0% for the first 3 feet
- C2.0% for the first 6 feet
- D1.0% for the first 10 feet
Show answer & explanationAnswer & explanation
Correct answer: C. 2.0% for the first 6 feet
A minimum positive drainage slope of 2% for at least the first 6 feet away from the foundation is a widely accepted standard. This ensures sufficient gradient to direct surface water away from the building, preventing moisture intrusion and foundation damage.
Why the other options are wrong
- A. 0.5% is generally too flat for reliable positive drainage away from a foundation.
- B. 3.0% is a very effective slope but might be excessively steep for a lawn area and is not the standard minimum for this distance.
- D. 1.0% can be acceptable in some areas, but 2% is a stronger recommendation for critical drainage near foundations.
Positive Drainage Slope (Foundation)
A minimum positive drainage slope of 2% for at least 6 feet away from a building foundation is crucial to direct surface water away from the structure.
- Prevents water pooling against foundations.
- Protects against moisture intrusion and structural damage.
- Slope should be continuous and uninterrupted.
- Equivalent to a 1/4 inch drop per foot.
Memory trick: Two percent for six feet, keeps the house neat!