Drainage below ground

Also see:

5.3.5Drainage system performance

Drainage shall be suitably located and prevent health hazards. Issues to be taken into account include:

  1. ventilation of drainage systems
  2. prevention of gases entering the home
  3. siting of septic tanks and cesspools
  4. pumped systems.

Ventilation of drainage systems

Ventilation of drains is normally achieved by ventilating discharge stacks.

Air admittance valves which comply with Technical Requirement R3 may be used in some homes to prevent trap seal siphonage. An open vent is generally required at the head of common drainage systems, and where the discharge pipe is the only vent for a septic tank or cesspool.

Prevention of gases entering the home

Where special precautions are necessary (e.g. sealing drains where they enter the building) to reduce the entry of gases such as radon or landfill gas, such precautions should be acceptable to NHBC.

Siting of septic tanks and cesspools

Septic tanks and cesspools should be:

  • a minimum of 7m from homes
  • a maximum of 30m from vehicular access to permit emptying.

In Scotland, a minimum distance of 5m from homes and boundaries is acceptable for septic tanks.

Pumped systems

Where a gravity system is not possible, pumped systems may have to be used and should be designed in accordance with BS EN 752 and BS 6297. The installation should include:

  • a holding tank of sufficient volume to contain 24 hours of domestic effluent based on 120L/150L per head per day
  • a suitable warning system providing visual and/or audible signals to indicate malfunction
  • suitable equipment housing.