What is a Patio Fall, and How Much Fall Should a Patio Have?

A patio fall or slope is the degree of decline or incline of the patio structure. The fall is required for adequate drainage of water from the patio surface, which would otherwise accumulate and damage the integrity of your patio. The fall is measured as an angle or as a percentage of elevation.

Why is Patio Fall Important?

The patio slope or fall ensures that any water from rain or spillage is not accumulated on the patio’s surface. If the angle of the fall is not enough or too steep, water can accumulate and damage the structure over time. Water pools will also make your patio look unpleasant and prevent you from using it during wet weather.

What Damage Can Water Do to Patios?

If the patio fall is not adequate and water is allowed to accumulate over the patio surface, it can damage your patio in several ways.

1. Cracking: Accumulated water will seep into existing cracks and will freeze during cold weather. This will cause the expansion of existing cracks and also create new ones. Excessive cracking will damage and deteriorate the patio structure and make it useless over time.
2. Staining: If water cannot drain from your patio surface and is allowed to sit for extended periods, the water pools will stain the patio surface. The stains will be too noticeable, especially on patio surfaces constructed from natural stone or concrete.
3. Erosion: Patios constructed from materials like limestone or sandstone will erode over time if the patio fall is inadequate and prevents adequate drainage.
4. Mould and Mildew: Frequent water pools over your patio surface will easily promote mould and mildew, damaging your patios and making them look unpleasant.
5. Structural Damage: Patios will settle down or sink because of ineffective water drainage, as over time, water will cause structural damage to the foundations of your patio.

How to Calculate the Right Patio Slope

The right patio slope has to be determined with as much accuracy as possible if you want the patio to last long. This includes determining the degree of decline/incline relative to the structure, which will allow effective drainage. The typical steps involved in this process are mentioned below.

1. Determining the Water Flow Direction: This is a visual observation which can help you determine the direction in which water flows which will let you identify the location of the patio slope.
2. Calculating the Slope: The fall is typically measured in terms of a percentage or an elevation angle. As a thumb rule, a fall of 2% or 1/4 inch per foot is generally considered the minimum slope for adequate water drainage, while a highly recommended approach is to keep a fall of 5% or 1/2 inch per foot. To calculate the slope, you have to divide the height difference between the low and high ends of the patio by the total length of the patio. As an example, if the length of your patio is 20 feet and the height difference between the low and high ends is 2 inches, the slope would be:

2 inches ÷ 20 feet = 0.1 inches per foot

To convert this to a percentage, multiply by 100:

0.1 inches per foot x 100 = 1% slope

1. Checking the Slope: Using a water level to check it throughout the patio’s surface after calculating the gradient.
2. Make Adjustments: If you find that the fall is inadequate for water drainage, you can alter it by removing or adding material from the patio base or changing the slope of the surrounding landscape.