How much fall should a patio have?
This is the question that many people ask when they begin to build their first patio. We’ve created a how-to guide for first-time patio builders on how to work out patio fall.
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Why is patio fall important?
Most patios will rely on the slope or ‘fall’ to carry away water. This helps prevent issues with water build up on your patio. Changing the gradient between the patio and drainage pipe can make sure water travels in the preferred direction. As such, you need to know how much fall will be enough for your patio.
How to calculate patio fall
Calculating the patio fall is a case of dividing the fall by the run. Typically, you can use the industry standard ratio for fall of 1:80. However, this could differ depending on your project. In this example, that means that the patio should fall 1 unit for every 80 units of distance. So in this example, to find the fall you need to divide the distance run by 80. This will provide you with the fall of the patio.
Now, let’s look at an example for a fall per metre patio. Let’s say that you have a patio that is 7 metres wide. The fall for this project is the industry standard which is 1:80. You now need to measure the fall per metre you need. In metres this is simply:
7 / 80 = 0.0875 metres
Once you’ve worked out how to calculate your patio fall, take a look at our step-by-step, beginner’s guide on how to lay a patio.
Where the slope starts and ends
To understand fall we need to know where a slope starts or ends on any patio. We do this by exploring how much the structure falls over a certain distance. Ultimately you will measure the distance of a structure. You can then see how far a structure rises or falls over that distance.
This will provide two values. The difference between the start and the end of the slope and the distance measured. Using these two values you can calculate the gradient or fall of the patio.
How patio fall is expressed
Using the two values, you will then be able to calculate and express falls that can be directly compared to others. These are commonly expressed in percentages such as:
Alternatively, you may also find that they are expressed in ratios. If that’s the case they will be expressed as :
- 10% is 1 in 10
- 5% is 1 in 20
- 20% is 1 in 5
This is a simple way of understanding the fall on patio. If the gradient is 1 in 5 this means that there is 1 unit of fall for every 20 units run. The units could be metres, centimetres inches or any other measurement.
How to convert between ratios and percentages
If you need to convert the ratio to a percentage, you simply need to divide by 100. This will provide you with a decimal figure that can be easily converted. So, you could have a percentage of 5%. The calculation would be:
100 / 5 = 20 so the ratio is 1 in 20 or (1:20)
To reverse this conversion, you can simply divide 100 by the nominal of the ratio. In this case that would be 100 divided by 20.
We hope this helps you understand the importance of the fall for your patio. Using this guide, you should be able to calculate the fall for any patio you need.