CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A C-27 contractor is installing a new concrete patio adjacent to a residential foundation. To ensure proper drainage away from the structure, what minimum slope percentage should the patio surface have, extending at least 10 feet from the foundation?
- A0.5%
- B2.0%
- C1.5%
- D1.0%
Show answer & explanationAnswer & explanation
Correct answer: B. 2.0%
For proper surface drainage away from a building foundation, a minimum slope of 2% (1/4 inch per foot) is generally recommended for impervious surfaces like patios, extending at least 10 feet. This ensures water moves away effectively and prevents accumulation near the foundation, which could lead to moisture damage.
Why the other options are wrong
- A. 0.5% (1/16 inch per foot) is often too flat for reliable surface drainage and may allow water to pond.
- C. 1.5% is better than 1% but still less effective than the recommended 2% for foundation protection.
- D. 1.0% (1/8 inch per foot) is acceptable for some flatwork but 2% is preferred for positive drainage away from structures.
Minimum Slope for Surface Drainage (Patios)
The minimum percentage of slope required for impervious surfaces like patios to ensure positive drainage away from building foundations.
- Typically 2% (1/4 inch per foot).
- Extends at least 10 feet from the foundation.
- Prevents water accumulation near structures.
- Protects foundations from moisture damage.
Memory trick: Two Percent Prevents Puddles Permanently.