To measure concrete slope, you determine the vertical change (rise) over a horizontal distance (run), ensuring both measurements are in the same units, then divide the rise by the run and multiply the result by 100 to get the percentage slope.
Measuring the slope of a concrete surface is crucial for various reasons, including proper drainage, accessibility compliance, and structural integrity. A common way to express slope is as a percentage. This percentage indicates the number of units the surface rises or falls vertically for every 100 units it extends horizontally.
Calculating Percentage Slope
The fundamental method for calculating slope involves two key measurements:
- Rise: The vertical difference in height between two points on the surface.
- Run: The horizontal distance between those same two points.
Here's how to calculate the percentage slope based on these measurements:
- Measure Rise and Run: Choose two points on the concrete surface. Measure the vertical distance between these points (the rise) and the horizontal distance between them (the run).
- Ensure Consistent Units: Convert the rise and run to the same units. This is a critical step to ensure the calculation is accurate. You could use inches, feet, centimeters, or meters, but both measurements must be the same.
- Divide Rise by Run: Divide the rise by the run. This gives you the slope as a decimal.
- Calculate Percentage: Multiply this number by 100 and you have the percentage slope.
Formula:
Percentage Slope = (Rise / Run) * 100
Example Calculation
Using the method described:
For instance, 3" rise divided by 36" run = . 083 x 100 = an 8.3% slope.
In this example:
- Rise = 3 inches
- Run = 36 inches
- Both are in the same unit (inches).
- Calculation: (3 inches / 36 inches) 100 = 0.0833... 100 ≈ 8.3%
Practical Tips for Measuring
To accurately measure the rise and run on a concrete surface:
- Use a Level and Measuring Tape: Place a long straight edge (like a 4-foot or 6-foot level or a straight piece of wood) on the surface, extending horizontally (use the level bubble to confirm it's horizontal).
- Measure the Run: The length of the straight edge resting horizontally on the surface is your 'run'.
- Measure the Rise: At the lower end of the straight edge, measure the vertical distance from the underside of the straight edge down to the concrete surface. This is your 'rise'.
- Ensure Accuracy: Take measurements carefully and repeat them to confirm accuracy. For longer distances, you might need to use string lines or surveying equipment.
Understanding the slope is vital for projects like driveways, patios, or ramps, ensuring proper water drainage away from structures and meeting building code requirements for accessibility (like ADA ramps).
