The new Part H drainage regulations is a great document that encourages specifiers to design more sustainable drainage systems associate and public health engineer at Arup. Here's his step-by-step guide to help you comply with requirements
1 - Preparation
  • Get a geotechnical survey of the site to determine, among other things, the height of the water table.
  • What does the ground consist of? As brownfield sites are being identified for redevelopment, "made-up" ground can cause problems for drainage installations.

    Steel and cast-iron pipes may rust in contaminated land and concrete may suffer sulphate attacks, which erode pipes. Ground contamination will also affect landfill disposal costs.

  • Check plans from any previous development. These could identify where obstructions are likely to be found.
  • Find out from the sewage undertaker whether a rodent problems exist. Some brownfield sites may come with a population of unwanted pests. The correct selection of material will reduce the likelihood of providing a new home for a rodent community.
  • Check with the sewage undertaker if the site is prone to flooding.
  • Can the ground receive storm water? Part H encourages ground disposal of water (such as soak-away designs) rather than systems that channel water into sewers or water courses that may flood during periods of heavy rain.

2 - Foulwater/rainwater drainage

  • Make sure that the rainwater and foulwater systems are kept separate.
  • Check there is a sewer nearby. In towns and cities it can be taken for granted, but in remoter areas it can be a luxury.
  • Protection of the installed pipework should be deep enough to prevent damage from site traffic.
  • Where possible run the drainage shallow. This will significantly reduce the costs associated with manhole construction. It will be less expensive to excavate a trench, and will create less waste, which means lower transport costs and a lower landfill tax for the project.
  • Check whether the sewer is to be adopted by the local authority. If so, then the underground drainage that runs beyond the curtilage of the building will be looked after by the local authority, which can determine the standard of the pipe connection.
  • If the sewer is within 3 m of the building, a new consent is required. Notify the local sewer undertaker before you start work on site.

3 - Waste treatment and cesspools

  • If a septic tank or on-site sewage treatment is required, find out what the ground water levels are. If the levels are high, then the treated outflow will not be able to be discharged into the ground.
  • If back flow could be experienced, then back flap valves should be considered. In buildings where the lowest internal level is below the outside ground level, water below ground level should be pump-discharged to the drainage system.
  • If the septic tank discharge is to be pumped away, find out where the discharge point is. Don't assume there is one nearby – you could have to pump the foulwater up to a mile away.


  • Consider plastic access fittings rather than brick structures. The approved document has examples of one-piece plastic fittings, which are cheaper than brick.
  • Check that the construction of the manholes is in accordance with health and safety legislation. The legislative impact of not passing health and safety regulations is far greater than not complying with Part H. Design the drainage system with as few manholes as possible and reduce the risk of injury from falls by making them shallower.
  • Check covers are on manholes.
  • Secure the manhole covers to prevent unauthorised entry.

Separating waste

  • Larger car parking areas may need to be designed to channel oil and petrol into separate drains to prevent water courses from being contaminated.
  • Separate grease from the waste created by commercial kitchens.
  • Make sure that there is somewhere to store refuse in new commercial buildings.


  • Carry out intermediate testing to identify leaks early on in the build programme. It's much easier to sort out leaks before the building is built over the top of the system.

Regulations: Part A - L