CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A C-27 contractor is preparing a site for a new concrete patio adjacent to a residential foundation. To ensure proper surface drainage away from the structure, what is the minimum recommended slope percentage for the patio surface?
- A3.0%
- B1.0%
- C0.5%
- D2.0%
Show answer & explanationAnswer & explanation
Correct answer: D. 2.0%
For hardscape surfaces like patios adjacent to structures, a minimum slope of 2% (1/4 inch per foot) is recommended to ensure positive drainage and prevent water from pooling against the foundation, which can lead to moisture damage.
Why the other options are wrong
- A. 3.0% (3/8 inch per foot) would provide excellent drainage but might be excessively steep for comfortable pedestrian use on a patio.
- B. 1.0% (1/8 inch per foot) is often considered a minimum for general landscape drainage, but 2% is preferred for impervious surfaces near foundations.
- C. 0.5% (1/16 inch per foot) is generally insufficient for reliable positive drainage on hard surfaces and can lead to ponding.
Minimum Patio Slope (Foundation)
A minimum slope of 2% (1/4 inch per foot) is recommended for patios and other hardscape surfaces adjacent to building foundations to ensure positive drainage away from the structure.
- Prevents water intrusion into foundations.
- Ensures reliable runoff on impervious surfaces.
- 1/4 inch of fall per 1 foot of run.
- Less than 2% can lead to standing water.
Memory trick: Two percent is the magic number for patio water to lumber!