CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A landscape contractor is grading a site for a new lawn area around a residential foundation. The design calls for a final grade that ensures positive drainage away from the house. What is the generally recommended minimum slope for the finished grade extending at least 10 feet from the foundation?
- A1% (1/8 inch per foot)
- B2% (1/4 inch per foot)
- C3% (3/8 inch per foot)
- D0.5% (1/16 inch per foot)
Show answer & explanationAnswer & explanation
Correct answer: B. 2% (1/4 inch per foot)
To ensure positive drainage and prevent water from pooling near a foundation, the finished grade of a lawn or landscaped area should have a minimum slope of 2% (or 1/4 inch per foot) extending at least 10 feet away from the building. This slope is effective for directing surface water away.
Why the other options are wrong
- A. 1% is generally considered too flat for reliable positive drainage on a lawn, as minor imperfections or settling could lead to ponding.
- C. 3% would provide excellent drainage but is not the minimum required; it might be used on steeper conditions or where faster runoff is desired.
- D. 0.5% is far too flat and would almost certainly result in standing water and poor drainage against the foundation.
Positive Drainage Slope (Foundation)
The finished grade around a residential foundation should have a minimum 2% (1/4 inch per foot) slope away from the building for at least 10 feet to ensure positive drainage.
- Prevents water accumulation near foundations.
- Protects against moisture intrusion and structural damage.
- Directs surface runoff to appropriate drainage systems.
Memory trick: Two percent out, no house water doubt.