Drains and sewers

This section has been written for homeowners who may be considering building an extension or making alterations. It outlines the main impacts that drainage may have on your project. If you decide to proceed with your project, your builder will need to look at Approved Document H¹ for detailed advice on how to comply with building regulations.  

What is drainage?

There are two systems of drainage that you need to think about: 'foul' and 'surface water'. In general, these two systems should be kept separate.

Each of these has above-ground and underground elements.

• Foul drainage carries the used water from toilets, sinks, basins, baths, showers, bidets, dishwashers and washing machines. The above-ground pipework is referred to as sanitary pipework; the underground pipework is referred to as foul drains and foul sewers
• Surface water drainage carries rainwater (and melted snow and ice) from hard surfaces. The above-ground system of gutters and rainwater pipes is referred to as roof drainage; the underground pipework is referred to as surface water drains and surface water sewers.

1. https://www.planningportal.co.uk/applications/building-control-applications/building-control/approved-documents/part-h-drainage-and-waste-disposal