Approved Document H of the Building Regulations, often referred to simply as Building Regulations Part H, outlines the drainage and waste disposal guidelines in dwellings and non-residential buildings.

Building regs part H, which came into force on 1 October 2015, applies to buildings in England as well as excepted energy buildings in Wales.

It covers the following aspects in great detail:

✅H1: Foul water drainage
✅H2: Wastewater treatment systems and cesspools
✅H3: Rainwater drainage
✅H4: Building over sewers
✅H5: Separate systems of drainage
✅H6: Solid waste storage

In order to get a clear idea of ‘what is Part H of the Building Regulations’, we’re going to take a closer look at what each section entails.

Table of contents:

Building Regulations Part H inforgraphic

What is the requirement H1 of the Building Regulations?

Section H1 stipulates the relevant regulations for foul water drainage.

But what is foul water drainage, to begin with?

Here’s the thing:

Foul water drainage refers to the system designed to collect and remove wastewater or ‘foul water’ from buildings. Foul water consists of wastewater generated from various sources such as toilets, bidets, sinks, showers, baths, dishwashers, washing machines and other plumbing fixtures.

To comply with foul water drainage Building Regulations, all domestic and small non-domestic buildings must have an adequate system to carry foul water to a public sewer, a private sewer connected with a public sewer, a septic tank or a cesspool.

On the other hand, complex systems in larger buildings must conform to British Standards BS EN 12056 – Gravity drainage systems inside buildings.


This section of Approved doc H, which is the longest and most detailed by far, further outlines the appropriate sizes of the components of the system. This includes the minimum trap sizes and seal depths of the various affected appliances, followed by branch connections to stacks to ensure crossflow prevention, branch discharge pipes and branch connections. The materials (cast iron, copper, uPVC and so on) and relevant standards for sanitary paperwork are also addressed.

As an alternative approach, the requirements could be met by following the aforementioned BS EN 12056.

When it comes to UK soil pipe Building Regulations, the system must also accommodate specific flow rates from dwellings. These range from 2.5 litres/sec for one dwelling to 5.8 litres/sec for 30 dwellings.

Finally, the section discusses the suitable materials and minimum sizes of access points to the system, such as manholes and inspection chambers, which must be large enough to allow for testing and inspection.

Rounding off section H1 of the approved document are three appendices which provide further clarification and guidance:

  • Appendix H1-A: Additional guidance for larger buildings
  • Appendix H1-B: Repairs, alterations and discontinued use of drains and sewers
  • Appendix H1-C: Adoption of sewers and connection to public sewers

What is the requirement H2 of the Building Regulations?

The requirement H2 states that any septic tank, wastewater treatment system or cesspool must be constructed and located in such a way as not to harm people’s health or contaminate a watercourse or water supply. It must also have adequate means of emptying and maintenance and have a means of protecting health in case of a power failure.

What’s more:

All septic tanks must be large enough for the number of dwellings they service, impermeable to liquids and adequately ventilated. Notices about any forthcoming maintenance of wastewater treatment systems must be made available across the dwelling(s).

Keep in mind that the use of these types of non-mains foul drainage should only be considered where a direct connection to mains drainage is impracticable or altogether not possible. In such cases, septic tanks must have a capacity below the inlet level of at least 2,700 litres for up to four users. After that, the size of the septic tank should be increased accordingly by 180 litres for any additional user.

As we already mentioned, this section of Part H of building reg pays close attention to the location or ‘siting’ of wastewater treatment plants and septic tanks.

They must be located:

  • At least 10 metres from a watercourse;
  • At least 50 metres from the abstraction point of any groundwater supply;
  • Not in a groundwater protection Zone 1;
  • At least 15 metres from any building;
  • At a sufficient distance from any drainage fields, soakaways or drainage mounds.

Further, Section H2 outlines how to carry out a percolation test as part of the preliminary assessment of the proposed location.

As with section H1, there is an alternative method of meeting the requirements by following the recommendations in BS 6297:1983 Code of practice for design and installation of small sewage treatment works and cesspools.

Finally, there is a single appendix – Appending H2-A: Maintenance of wastewater treatment systems and cesspools.

What is the requirement H3 of the Building Regulations?

Section H3 elaborates on rainwater drainage regulations in the UK. In order to ensure H3 compliance, there must be adequate provisions for rainwater to make its way down from the building’s roof into a soakaway, infiltration system, watercourse or sewer.

Additionally, paved areas surrounding the building which provide access to it must also have adequate drainage.

Section H3 further addresses standard downpipe and gutter sizes in relation to rainfall intensities across England and Wales, followed by the regulations on surface water drainage. A single appendix – Appending H3-A: Oil separators – completes this section.

What is the requirement H4 of the Building Regulations?

Section H4 regulates construction work over drains, sewers or disposable mains or any areas which affect access to any drain. Before proceeding with any such construction, the developer must contact the owner of the sewer or drain and undertake special measures where appropriate.

Bear in mind that buildings or extensions must not be erected within 3 metres of any drain or sewer which is more than 3 metres deep or larger than 225mm in diameter without the explicit permission of the owner.

What is the requirement H5 of the Building Regulations?

The penultimate section of Part H Building Regulations, H5 addresses separate drainage systems, stating that ‘any system for discharging water to a sewer’ in accordance with section H3 ‘shall be separate from that provided for the conveyance of foul water from the building’.

This provision is aimed at minimising the amount of rainwater which enters the public foul sewer system, thus preventing dangerous overload in case of flooding.

What is the requirement H6 of the Building Regulations?

Last but certainly not least, the requirement H6 mandates adequate provisions for the storage of solid waste. This includes adequate access to the place of storage for all occupants of the buildings as well as from the place of storage itself to a suitable collection point.

The number and size of the required containers are specified by Sections 46 (household waste) and 47 (commercial waste) of the Environmental Protection Act 1990. In order to ensure section H6 compliance, there must be consultation with the waste collection authority to clarify their specific requirements.

Finally, there is a single appendix – Appendix H6-A: Relevant waste collection legislation – which provides a convenient reference point.

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Final thoughts

Proper design, installation and maintenance of foul water drainage systems are crucial to ensure the effective removal of wastewater, prevent blockages and minimise the risk of odours, contamination and health hazards.

Building regulations and guidelines, such as Building Regulations Part H in England and Wales, provide specific requirements and standards for foul water drainage to ensure compliance and safety.

Keep in mind that approved documents are subject to revisions and changes every few years. So, always make sure to consult the latest version of each document and secure building regulations approval before embarking on any project which might be affected by Building Regs Part H.

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