Decide on the slope you want for your patio, which we recommend to be 1 inch for every 4 to 8 feet. For a 20-foot patio, this could be a total drop of 5 inches if you want a steeper slope.
In general, a slope of 1/8 to 1/4 inch per foot is considered a good starting point for patio slope. This means that for every 12 to 24 feet of horizontal distance, there should be a 1-inch drop in elevation.
You want -at least- 1% slope away from the house in at least one direction. 2% would be great. 4-5% would be maximum.
The standard ratio for a fall is 1:80 (1 unit of fall for every 80 units of distance). For example, to calculate the fall for a patio that is 5m in length you would simply need to divide 5 by 80 which would give you 0.0625. This would mean your 5 metre patio should have a total fall of 0.0625m or 6.25cm.
Measure With Tape and Level
The rise is the vertical height of the slope, and the run is the horizontal distance. To calculate the slope, divide the rise by the run and multiply by 100 to get a percentage. For example, if the rise is 6 inches and the run is 10 feet, the slope would be (6/120) x 100 = 5%.
If you have a square or rectangular patio then calculating its area is quite a straightforward job. You simply need to measure the width and length of the area that you're looking to pave and multiply the two numbers together. This will then give you your area to pave.
A gradient of 1:60 means that there will be 1 unit of fall for every 60 units of patio width. The patio is to be 4.2m wide, so if that distance (the run) is divided by 60, the result is the 1 unit of fall. We'll work in millimetres rather than metres... From the above.... Fall = 4,200mm ÷ 60 = 70mm.
A fall is a gentle gradient in the sub-base that allows proper drainage and ensures water runs away from the house. The ideal gradient for a non-textured slab is 1:60, a 16mm drop in level per metre. When working with a textured slab, the target gradient is 1:80, with around 12.5mm drop per metre.
A patio should slope away from the house at the rate of 1/8" (3mm) per running foot. Generally, a 4" (100mm) thick slab set 2" (50mm) above ground level is suitable.
Vertical Fall (meters) = (Horizontal Distance / Gradient)
This formula divides the horizontal distance by the gradient to find the vertical fall in meters.
The ideal slope for proper yard drainage typically ranges between 2-3%. Creating a subtle slope away from your home allows water to flow away naturally and prevents accumulation near the foundation.
STEP BY STEP GUIDE TO LAYING A PATIO
Dig a depth of around 150mm across the whole area, making sure the soil is evenly compacted. Then tip in the sub-base, raking it into a consistent depth of 100mm. Make sure it's smooth, flat and firm.
Even though it's possible to build a concrete patio without rebar, it's not recommended. All concrete is subject to cracks, but rebar holds all the cracks together and keeps the slab level and even. Without rebar, the cracks would become quite wide and the concrete would become uneven.
A too-steep slope could lead to water pooling on the patio, while a too-gradual slope might not allow proper drainage. It's best to follow the recommended slope of 1" for every 4'-8', but you can adjust this according to your preference.
If your patio is not level, water can pool in certain areas and freeze in winter, creating dangerous conditions for anyone who uses your patio. In addition, unlevel patios can be unsightly and make it difficult to furniture or other items on your patio.
The short answer here is that it should slope enough to drain water in the right direction but not so much that you can visibly see or feel the slope. Usually, this comes out to a quarter inch drop for every one foot or 2%.
Ensure that all patio slabs, porch slabs, walks, driveways, and other impervious surfaces that are installed within 10 feet of the foundation slope down and away from the foundation at a 2% grade. Maintain this slope for 10 feet or to the edge of the surface, whichever is less.
The recommended depth you'll want to dig to is about 150mm or 6 inches from the finished patio level. You can use a tape measure to check your depth is correct and once you're happy you can compact the soil using a Vibrating Plate compactor, also known as a Wacker Plate.
Slope Guidelines
If the pitch is too shallow, the cover can trap water and cause drainage problems. The minimum slope for a patio roof is 1/4 inch per 12 inches of run. However, you can increase the pitch if needed. Your cover should match your home's roof.
Plan for the proper slope. The patio needs to slope away from the house — about a 1-inch drop every 4 feet. A 4-foot level with a 1-inch block of wood attached to the end is helpful to check the slope as you're digging. Use your yard's natural slope if possible.
Most patios will rely on the slope or 'fall' from a patio 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.
Now if you say that something is 100 feet long or 100 inches long, then 1% is 1/100 of that length. Now when it comes to slopes it means that for 100 feet in length, the slope would be 1 ft up or down in every 100 feet.
Q: What should the fall (gradient) of my paving or patio be? A: An 80:1 gradient is recommended for the fall. To calculate this, divide the length of the paved area (the run) in millimetres by 80 to give you the correct fall in millimetres.
It establishes the following limits: Minimum slope: 1:20, meaning you will have 20 units of horizontal length (run) by 1 unit of vertical length (rise). Maximum slope: 1:12, meaning you will have 12 units of horizontal length (run) by 1 unit of vertical length (rise).