Proper gradients and falls are essential for adequate drainage and runoff when installing pavers, concrete, or drainage pipes. This comprehensive guide covers everything you need to know.
What are the different types of falls?
There are two types of falls used in paving and drainage projects. Endfall is when the slope is oriented along the length of a surface or pipe. Also called the longitudinal slope. This is the direction in which water flows. Crossfall is when the slope is oriented across the width of a surface or pipe. Also called the transverse slope. Crossfall facilitates drainage across the width of a surface.
The directions of endfall and crossfall may be arbitrarily defined for large, open areas without a clear orientation. But in drainage, landfall always follows the intended direction of water flow.
How is the gradient for patios calculated?
The patio gradient, or fall measures the steepness of a slope. It is defined as the change in elevation or vertical drop (rise or fall) divided by the horizontal distance (run).
Gradient = Rise/Run (rise divided by run)
The gradient is expressed as a dimensionless ratio. This allows the comparison of slopes regardless of measurement units used.
For example, a rise of 1 inch over a run of 20 inches has the same gradient ratio as a rise of 1 foot over 20 feet. In both cases, the ratio is 1/20.
Visualising different gradients as ratios provides an intuitive sense of relative steepness. For example, a ratio of 1/100 is a flatter slope than 1/10.
How are falls and slopes expressed?
Gradients are typically expressed as either percentages or ratios:
Percentages
A rise of 1 unit over a run of 100 units is a 1% grade. Similarly, 1/20 is a 5% grade, and 1/2 is a 50% grade.
Ratios
A rise of 1 unit over a run of 20 units can be expressed as 1:20. 1/10 is 1:10, and 1/2 is 1:2.
How do you convert ratios to percentages?
To convert between gradient percentages and ratios:
Percentage to Ratio: Divide 100 by the percentage (e.g. 100/5 = 1:20)
Ratio to Percentage: Divide 100 by the denominator (e.g. 100/20 = 5%)
How can you calculate the fall per meter?
To determine the fall per meter, divide the specified ratio by the run distance.
For example, a 1:100 gradient over a 10-meter run equals 1/100 = 0.01 = 10mm of fall per linear meter.
How much fall should garden paving have?
For Paving, a minimum 1:40 slope is recommended. Use 1:60 to 1:100 for better drainage. Crossfall is typically half the endfall slope.
How much fall should drainage pipes have?
For drainage pipes, a minimum fall of 1:60 is recommended. 1:100 is better for slower drainage flow. Up to 1:10 maximum to avoid excessive velocity and erosion.
What are some examples of calculating fall?
Patio Gradient
A 12-meter-wide patio with a 1:80 gradient
- Rise = 1 unit
- Run = 80 units
- Fall per meter = 1/80 = 12.5mm
- Total fall across patio = 12 * 12.5mm = 150mm
Drainage Pipe
A 30-meter-long drainage pipe with a 1:100 gradient
- Rise = 1 unit
- Run = 100 units
- Fall per meter = 1/100 = 10mm
- Total fall over length = 30 * 10mm = 300mm
After understanding the intricacies of falls and gradients for effective drainage, choosing the right paving material becomes paramount. Sandstone paving, with its natural and rustic charm, offers durability and excellent traction, especially when wet, ensuring swift water runoff. In contrast, the modern allure of porcelain paving, known for its stain resistance and minimal water absorption, provides a sleek finish. However, it’s vital with porcelain to get the gradient spot on, ensuring water doesn’t pool on its smooth surface. Patio packs are an excellent choice for those seeking convenience and design variety.
