CSLB C-27 Landscaping ContractorSite Preparation and DrainageEasy
A landscape contractor is planning to install a new concrete patio adjacent to a residential foundation. To ensure proper drainage and prevent water from accumulating against the foundation, what is the minimum recommended slope for the patio surface away from the building?
- A0.5% (1/16 inch per foot)
- B1% (1/8 inch per foot)
- C3% (3/8 inch per foot)
- D2% (1/4 inch per foot)
Show answer & explanationAnswer & explanation
Correct answer: D. 2% (1/4 inch per foot)
A minimum slope of 2% (or 1/4 inch per foot) is widely recommended for concrete patios and other hardscape surfaces adjacent to buildings. This slope ensures positive drainage, effectively directing water away from the foundation and preventing moisture issues.
Why the other options are wrong
- A. 0.5% (1/16 inch per foot) is generally too flat for effective surface drainage on a patio, especially with minor settling or imperfections.
- B. 1% (1/8 inch per foot) might be acceptable for very short distances or specific conditions, but 2% is a safer minimum.
- C. 3% (3/8 inch per foot) is a good slope for drainage but not the minimum; it might be used on longer runs or in areas requiring faster runoff.
Minimum Patio Slope (Foundation)
A concrete patio adjacent to a building foundation requires a minimum 2% (1/4 inch per foot) slope away from the structure for positive drainage.
- Prevents water intrusion into foundations.
- Reduces risk of efflorescence and mold.
- Ensures runoff is directed to appropriate drainage.
Memory trick: Two percent, no wet foundation lament.