CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A C-27 contractor is overseeing the final grading of a residential backyard. The design calls for a final grade that slopes away from the house foundation to ensure positive drainage. If the patio adjacent to the house is 10 feet wide and the grade drops 2.5 inches over that distance, what is the percent slope?
- A2.5%
- B1.5%
- C2.0%
- D2.08%
Show answer & explanationAnswer & explanation
Correct answer: D. 2.08%
To calculate percent slope, divide the rise (vertical drop) by the run (horizontal distance) and multiply by 100. First, convert all units to feet: 2.5 inches = 2.5 / 12 = 0.2083 feet. Then, (0.2083 feet / 10 feet) * 100 = 2.083%, which rounds to 2.08%.
Why the other options are wrong
- A. Incorrect calculation; 2.5% would be a drop of 3 inches over 10 feet.
- B. Incorrect calculation; 1.5% would be a drop of 1.8 inches over 10 feet.
- C. Incorrect calculation; 2.0% would be a drop of 2.4 inches over 10 feet.
Percent Slope Calculation
Percent slope is calculated as (Rise / Run) * 100, where 'Rise' is the vertical change and 'Run' is the horizontal distance, with both in the same units.
- Formula: (Rise / Run) * 100.
- Ensure consistent units (e.g., all feet or all inches).
- Used to determine drainage effectiveness and maintainability.
- A 2% slope is 2 feet of drop over 100 feet of run.
Memory trick: Rise over run, times one hundred, the slope is done.