A consultation with a landscape designer provided us with these helpful tips: Patios must have a slight slope (1" for every 4' to 8') for proper drainage. If you don't provide enough slope, rainwater will settle into low spots, eventually softening and washing out the sand and subbase materials beneath.
Tip: It is essential that rain water flows off the paving and away from buildings. To ensure this paving must not be completely flat, it should slope about 20mm (2cm) per metre.
Pavers are great for patios, since they allow water to seep through and not form puddles and pools.
In general, the slope should be gradual enough to prevent water from pooling around the pavers, but not so steep that the pavers will become unstable or prone to shifting. A common guideline is to have a 1-2% slope away from any structures, such as a house or building, to ensure proper drainage.
Top tip - Drainage in the middle of a patio
You can fit a drainage channel in the centre of a paved area. The paving either side should slope towards the channel edges, and the channel should have a fall of 1 in 80.
Gradients from 1 in 40 to 1 in 110 will normally give adequate flow velocities. If the gradient is steeper than 1 in 40, the liquid may run faster than the solids in the sloping foul water pipe.
For 100mm pipes, the type normally used for residential drainage, the minimum acceptable falls are 1:40 for Foul Water and 1:100 for Surface Water. Larger diameter pipes may have gentler gradients in certain circumstances.
It's also important that you ensure that your concrete or stone pavers are properly leveled because uneven surfaces will not only be an eyesore but also become unsightly over time. As they will develop cracks and chips easier due to the uneven terrain they were placed on.
If using textured paving slabs – the ideal fall for a patio is 1 in 80. That is a 12.5mm drop in level per metre. If using flat or smooth paving slabs - aim for a fall that is 1 in 60. That is a 16mm drop in level per metre.
Laying the Pavers
Set pavers lightly on the sand, NEVER press or hammer them into the sand bed. It is important to maintain straight lines in the pavers. To check for straight lines run a string from one end of the surface to the other over the laying edge of the pavers.
If your backyard doesn't have a natural slope, you can install a filter fabric or geotextile as they are commonly called. They are made of a permeable material that prevents the subgrade from moving while allowing water to drain. By installing this underneath your pavers, you could extend the lifespan of your patio.
Concrete sand, also known as bedding sand, is coarse and doesn't trap excess moisture beneath the paver surface. This allows pavers to drain after a heavy rain and maintain their structural integrity over time.
Try permeable pavers
Permeable pavers are a great option for ensuring that you have adequate drainage for your pavers. You can even use a strip of permeable pavers as a type of french drain at the bottom edge of your driveway, along a fence line, or next to your house.
When it comes to building a patio, it should always slope away from the house. The reason why you don't want it to slope inward is that it can collect an excessive amount of water and direct it towards your property. Whenever there's too much water around your foundation, problems are bound to arise.
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.
Slope is a ratio of inches per foot, the minimum slope is 1/4" per foot and the maximum slope is 1" per foot, the maximum slope is the most the cover can be pitched and the roof panels maintain a proper contact with the hanger and beam.
Adding a step down can help prevent water damage and dreaded water damage restoration expenses. If you decide not to build a step down to a deck, invest in water-resistant materials and waterproof seals to prevent water damage.
The recommended space between the pavers is 3 mm (⅛”).
Keep in mind that the slope should be at least 1 inch for every 8 feet of the paver patio. For instance, a 16-foot patio will require 2 inches of the slope while a 12-foot patio will require 1 1/2 inches of the slope. You need to measure the calculated slope from the string tied at the drainage end of the patio.
A GRAVEL BASE LAYER BEFORE SAND IS A MUST! Using sand alone to set pavers is not enough. The best and recommended paver base is 3/8-inch crushed gravel.
Often, homeowners want to put pavers over top of existing concrete because it's much better than the alternative: tearing up the underlying concrete first, which is a messy and potentially expensive job. Fortunately, you can put pavers directly over existing concrete.
Design documents generally recommend a 1 to 2 percent slope. Stormwater velocities within the channel become too high on steeper slopes, causing erosion and preventing infiltration or filtering in the swale.
What is a 1 in 40 fall? A 1 in 40 pipe fall means that for every 40 units of length, the pipe will drop by 1 unit. For example, in a 40 metre run of pipe, the vertical drop of that pipe run will be 1 metre. It makes no difference what unit of measurement is used. Pipe fall can also sometimes be described as a gradient.