A paved surface must drain well for the surface to perform correctly. A poorly drained surface will allow pools of water to develop which will encourage algal growth and moss, or ice in winter. The paved surface will become slippery and dirty and the structure of the stone itself may deteriorate.
Water is removed from the paving surface by making use of gravity. The paving surface should not be laid flat but should slope 'be laid to a fall'. The 'falls' will generally be between 1:80 (for every 80cm the path will fall away by 1cm) to 1:40. A small patio can often be laid to a simple fall to adjacent land, however more preparation and planning will be required for larger paved areas and will require the use of gullies, channels, linear drains and manholes in conjunction with soak-aways or attenuation systems. For detailed instructions on the installation of drainage systems please visit the links at the bottom of the page.
Where the water from the surface drains too should also be considered. The run off from a paved surface could flood adjoining land, or turn adjacent ground into a boggy mess. The correct disposal of this run off should be considered so that it avoids damaging adjacent land, and ideally is allowed to be slowly absorbed into the ground.
The simplest method is to drain the water to adjacent land where the land will absorb the run off. For this to work the ground needs to be free draining in both summer and winter, be part of the property being drained (i.e. not your neighbour's land or a public highway!), and less than 2m of drainage width.
If the length of drainage is much over 2m then some form of soak-away, or the more effective attenuation system should be used. These will act as a store for the surface water run off, which will then slowly drain into the soil. If your soil is already waterlogged or impermeable (i.e. clay) then a soak-away system will not work.
Join to a surface water system. Planning permission will be required for this and will only be considered if the two alternative solutions shown above are not suitable. Allowing your run off to enter a surface water drainage system has the effect of moving your drainage problem further downstream where it can help to cause flooding. Legislation in the form of Sustainable Urban Drainage (SUDs) was implemented to try and reduce the risk of flooding being exacerbated by the run off from urban paved areas. Rainfall in the countryside will take time to reach drainage systems with as much as 95% being absorbed into the soil, while in an urban environment as little as 5% will be absorbed with 95% immediately 'running-off' into the drainage systems and rivers. Increased urbanisation and changes to rainfall patterns has resulted in more flooding events at huge monetary and personal cost. Storm water run-off also tends to wash pollutants into river courses and slows the re-filling of valuable underground aquifers. The SUDs legislation puts an obligation on landowners to ensure that run off from paved areas goes to soak-away systems so that the water is prevented from running off into drainage systems.
Surface water drainage should not be allowed to enter the foul water sewerage system. Cleaning up foul water is expensive and there is no reason to treat the relatively clean surface water run off, unless of course you want your water bills to rise? Secondly where surface water has been allowed to enter the foul system it can overwhelm the sewerage treatment plants during storm surges with the result that un-treated sewerage can overflow into our watercourses or the sea. Not nice!
For a more detailed guide to drainage, check out Drainage Expert, the Interim Code of Practise for Sustainable Drainage Systems and Guidance on the Permeable Paving of Front Gardens
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