Because of their easy installation and efficiency as drainage channels, linear drainage systems are very popular and can commonly be seen acting as edging for block paving, concrete and brick patios.
Top tip - Drainage in the middle of a patio
The paving either side should slope towards the channel edges, and the channel should have a fall of 1 in 80.
Approaches vary by LPA, but a typical drainage strategy usually defines: the site's characteristics (slope profile, soil geology, existing flood risk) the calculated surface water runoff rates and required storage volumes.
Dig a trench from the place in your yard that needs drainage to your chosen outlet. Check for underground utility lines and pipes before digging. The trench should be about 18 inches deep and 9 to 12 inches wide.
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.
This is usually calculated at 80:1 drop per metre in the direction you want the paving to drain (e.g. 12.5mm drop per meter), but a ratio of 60:1 can be used when necessary if the paving surface requires more assistance.
However before you lay down any paving slabs, you should consider a patio drainage system. By ensuring the removal of standing water from a patio (which can happen as a result of heavy rainfall) a properly installed drainage system can help you to avoid bacteria growth and even insect infestations.
A drainage system costs $10 to $25 per linear foot or $1,000 to $4,000 for exterior yard and landscape applications, and $40 to $85 per linear foot or $4,000 to $12,000 for a basement or interior perimeter drain. An exterior footing or drain tile installation costs $6,000 to $15,000.
To promote proper drainage, your yard and landscaping should have a slope of at least 3% directed away from your home's foundation, and generally between 3-10%, though grades of anywhere from 3% to 25% may be acceptable.
Drainage Patterns. Drainage Pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. The pattern created by stream erosion over time reveals characteristics of the kind of rocks and geologic structures in a landscape region drained by streams.
Use Slopes to Achieve Optimal Drainage Conditions
According to the EPA, patio slabs, walks and driveways need a minimum slope of 1/4 inch per foot away from the house with back-fill to prevent settling. The final grade must be sloped away from the foundation by 1/2 inch per foot over a minimum distance of 10 feet.
Pavers are permeable and are laid with small spaces in between them. These features allow water to run through them and back into the ground below instead of sitting on top, like it would with asphalt or concrete.
A good rule is to use a minimum slope of 2%, which is equivalent to a 1/4-inch drop for every foot of length.
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.
Fortunately, there are easy-to-install solutions for a drain in concrete patio borders or other areas to carry the water away. You can install a swale or French drain, which channels the water away from the site to an area where it won't cause problems.
If the existing concrete patio lacks a drainage system, it is a practical move to install one. In areas where the rainwater collects, cut a sloping channel. A well-cut channel directs the water away from the patio. Fill the channel with decorative stones or gravel so it meets aesthetic ideals.
A well-planned drainage system prevents common pitfalls such as water pooling, erosion, and damage to your property's foundation. Investing time in selecting the right drainage solutions pays off by keeping your patio dry and functional year-round.
All drainage pipes should be placed on the gravel bed in the trench. PVC drainpipe, if used, should be placed in the trench with the holes facing down.
Pipe for conveying liquids susceptible to freezing should be buried no less than 12" below the maximum frost level. Permanent lines subject to heavy traffic should have a minimum cover of 24". For light traffic, 12" to 18" is normally sufficient for small diameter pipe (typically < 3" diameter).
Clay soil has poor permeability, meaning it doesn't allow water to pass through easily. In such cases, the effectiveness of a French drain may be limited as the water may struggle to drain away from the area efficiently. French drains may not be suitable for areas with high water tables.