BS EN 752 explained: the standard for drains and sewers outside buildings

BS EN 752 is the British and European standard for drain and sewer systems outside buildings. It sets out what those systems have to achieve, and how they should be managed through planning, design, construction, operation and rehabilitation. The objectives are broad: carry the flow reliably, protect public health, keep wastewater out of watercourses and groundwater, and hold together for the design working life.

What it no longer does is tell you how to size a pipe. The 2017 revision moved every hydraulic design requirement out of the standard and into a separate document, and much of the confusion still surrounding BS EN 752 comes from specifications, statutory guidance and websites that have never caught up with that change.

BS EN 752 tells you what a drain or sewer system has to achieve. It stopped telling you how to size the pipes in 2017.

What is BS EN 752?

BS EN 752 is the standard titled Drain and sewer systems outside buildings. Sewer system management. The current edition is BS EN 752:2017, the UK implementation of the European standard EN 752:2017. BSI published it on 9 March 2018, and it now incorporates corrigenda issued in October 2019 and February 2022. It supersedes BS EN 752:2008.

• What it is. The UK implementation of EN 752:2017, the European standard for managing drain and sewer systems outside buildings.
• Current edition. BS EN 752:2017, incorporating the corrigenda of October 2019 and February 2022.
• What it replaced. BS EN 752:2008, withdrawn.
• Who writes it. CEN Technical Committee 165, Waste water engineering, mirrored in the UK by BSI committee B/505/22, Drainage Systems Outside Buildings.
• Status. Current, and listed by BSI as under review.

The British version carries a UK National Annex setting out how the European text should be applied in this country, and it is the part of the document a UK practitioner is most likely to want. It exists only inside the paid standard. There is no way to read it short of buying a copy.

What BS EN 752 covers, and where it stops

BS EN 752 applies from the point where wastewater leaves a building to the point where it discharges into a treatment works or a receiving water. It covers gravity systems of all three kinds: foul, surface water and combined. It also picks up drains running beneath a building where those drains are not part of that building's own drainage. Everything inside the building is governed by a different standard.

That boundary matters more than it sounds. A good many drainage queries in planning come down to two parties applying different standards to the same run of pipe. On a development it is the external side that carries the weight, because that is where a surface water drainage strategy for planning has to demonstrate rate, volume, destination and quality. The standards set out below sit behind all four of those tests.

The boundary is the building itself. Inside it, BS EN 12056. Outside it, BS EN 752 and its design companions.

From seven parts to one management standard

BS EN 752 has been through three generations, and each change moved content rather than deleting it. That is why withdrawn part numbers are still quoted so widely, and why a search for the standard turns up as many superseded documents as current ones.

1. 1996 to 1998: seven separate parts. BS EN 752-1 to -7 covered generalities and definitions, performance requirements, planning, hydraulic design and environmental considerations, rehabilitation, pumping installations, and maintenance and operations. Part 4 held the hydraulic design rules, which is why it is still the most searched-for of the seven.
2. 2008: one document. BS EN 752:2008 consolidated all seven parts into a single standard and also superseded BS 8005-0:1987. The seven parts were withdrawn.
3. 2017: a management standard. BS EN 752:2017 kept the objectives, the requirements and the management framework, and moved the design content out to a new family of companion standards.

Every earlier edition is withdrawn. A PDF of BS EN 752-4:1998 circulating on a document-sharing site is a superseded document that has been out of force for eighteen years, and building a design on it is a reliable way to have the calculations queried on review. Check the front matter before you rely on anything.

Where the design numbers went

The 2017 revision took the hydraulic design content out of BS EN 752 and put it into BS EN 16933-2. The standard says so itself, in its European foreword.

BS EN 16933-2:2017, Drain and sewer systems outside buildings. Design. Hydraulic design, was published on 31 October 2017 and gained a UK National Annex through a corrigendum the following June. Its clause 6 carries the design criteria, and clauses 7 to 10 cover pipeline capacity, incoming flows, hydraulic calculation, and the design of inlets, manholes, overflows and tanks. Pumping went to the BS EN 16932 series. The physical layout requirements that also left the old clause 9 became Annex D of BS EN 752 itself.

This leaves the frequency tables in an awkward position. The figures people mean when they say "BS EN 752 requires" come from Tables 1 and 2 of the 2008 edition, which is withdrawn. They are set out below because they are what is being cited, not because they are current.

The rule that governed them was that no surcharge should occur during the design storm. Their current equivalents sit in clause 6 of BS EN 16933-2 and in the UK National Annex added to it by the 2018 corrigendum, neither of which is published anywhere outside the paid standard, so a figure quoted online without an edition attached to it has almost certainly not been checked against the source. It is also worth being clear about what these frequencies actually mean before using them, because a 1 in 30 year event describes an annual probability rather than a schedule.

What each clause of BS EN 752 does

The standard runs to twelve clauses and four annexes. Read as a whole it is a management framework rather than a design manual, and the clause order follows the life of an asset, from the objectives it has to meet through investigation, planning, design and construction to operation, maintenance and the competence of the people carrying that out.

• Clause 4, objectives. Four things the system exists to deliver: public health and safety, occupational health and safety, environmental protection and sustainable development.
• Clause 5, requirements. The functional requirements, how measurable performance requirements are derived from them, and how design criteria are set beyond those to allow for change over the design working life.
• Clause 6, integrated sewer system management. Investigation, assessment, planning and implementation: the cycle an asset owner runs.
• Clause 8, design. System types, layout, hydraulic, environmental, structural and operational design, now largely pointing outwards to the companion standards.
• Clauses 9 to 11. Construction, operation and maintenance, and the qualifications and training expected of the people doing the work.
• Annexes A to D. Sources of information by country, rehabilitation approaches, operation and maintenance techniques, and the normative Annex D on physical layout.

Clause 5 is the closest the standard comes to a plain statement of what good looks like. A system has to prevent sewer flooding at the frequency the country prescribes, allow safe access for maintenance, keep pollution out of surface water and groundwater, exclude odours and toxic or explosive gases, stay watertight, hold its structural integrity for the design working life, and convey the permissible flows reliably. Note the phrasing on flooding: the frequency is left to national practice, which is precisely why the UK figures come from somewhere else.

Pipe full, surcharged and flooded

BS EN 752 draws a careful distinction between a pipe running full, a surcharged system and flooding. On site the three get treated as one thing, and they are not. A surcharged sewer is doing its job under pressure; a flooded one has been exceeded.

The standard's separate definition of sewer flooding repays a second reading: a condition where wastewater escapes from, or cannot enter, a drain and sewer system. That second half catches the case most people miss, which is the gully that will not take the rain because the sewer beneath it is already surcharged to the point where nothing more can get in. Nothing has burst. Nothing is leaking. The water simply has nowhere to go, so it stays on the road and finds the low point on its own.

Surcharge is a pressurised pipe. Flooding is water where it should not be. A design is judged against both, at different frequencies.

What actually sets the numbers on a UK scheme

On a UK development the design criteria come from the Design and Construction Guidance and from the Lead Local Flood Authority, not from BS EN 752 directly. The DCG is Appendix C to the Sewerage Sector Guidance, currently at version 2.3 of November 2023, and it is what a sewer offered for adoption in England is judged against. It sends hydraulic design straight to BS EN 16933-2. Connecting to an existing public sewer is a separate process again, under Section 106.

• Hydraulic design. Clause C6.1.2 requires pipelines and other conduits to be designed in accordance with BS EN 16933-2.
• Where BS EN 752 survives. Clauses B5.1.15 and B5.2.31 cite it for layout and for the provision of access, not for sizing.
• No surcharge above the soffit. Clause C6.4.3 sets the 1 year event where average ground slope exceeds 1%, the 2 year event where it is 1% or flatter, and the 5 year event where the consequences of flooding would be severe, such as existing basements beside the site.
• Roughness. Clause C6.4.2 sets a Colebrook-White roughness of 0.6 mm for surface water sewers and lateral drains.
• The 1 in 30 year check. Clause C6.1.6 requires the designer to show that the upstream system, gullies and permeable paving included, can actually deliver flows to any component sized above that event.
• Climate change and urban creep. Clause C6.2.1 leaves the design rainfall frequency and duration, and the allowances applied to them, to the local authority.

That last clause is the one to take away. Two identical schemes in neighbouring authorities can end up with different storage volumes and different discharge rates, because the framework is national while the numbers that go into the model are set locally by the authority and its drainage consultee. It is also why a strategy quoting a national table instead of the council's own published requirements so often comes back with a request for further information, and why discharging a drainage condition takes longer than it should.

Where UK guidance still points at withdrawn editions

The statutory guidance in England, Wales and Scotland all cite editions of BS EN 752 that no longer exist. This is a documentation lag rather than a trap, but it wastes real time for anyone who goes looking for the clauses they have been told to follow.

Parts 3, 4 and 6 were withdrawn in 2008. Approved Document H also sends the reader to "Annex ND in BS EN 752 Part 4" in the note to Table C1, and that annex went with the part that contained it. The Welsh Government's 2023 republication of the Part H guidance carries the same paragraph unchanged. In Scotland the Building Standards Technical Handbook 2020 cites BS EN 752:2008 at clauses 3.7.3 and 3.7.4, for external drainage construction and for disconnecting inspection chambers, and that edition was withdrawn in 2017.

Approved Document H still directs designers to three parts of BS EN 752 that were withdrawn eighteen years ago.

The practical answer is to read the current standard and treat the intent of the guidance as the requirement. Where an Approved Document points at a clause in a withdrawn part, the equivalent material has not disappeared: it now sits either in BS EN 752:2017, in the normative Annex D that absorbed the old physical layout content, or in BS EN 16933-2. Nobody has ever been criticised for using the current version of a standard. It helps to remember that Approved Document H is the building control test rather than the planning one, and the two run on different documents.

The wider family of drain and sewer standards

BS EN 752 sits at the head of a family. It states the objectives; the companion standards carry the detail on design, pumping, construction, investigation and vocabulary. Knowing which document holds which subject is most of the battle, because the subject you want is rarely in the standard you were pointed at.

Four of these come up constantly in practice. BS EN 16933-2 is the design document. BS EN 1610:2015 governs construction and testing, and is what a contractor is working to on site. BS EN 13508 covers investigation and the condition coding that appears in CCTV survey reports, so it is the one a purchaser meets without ever knowing its number. BS EN 16323 is the vocabulary standard the 2017 revision aligned its terminology to, which is why the definitions quoted above are worded the way they are. For the structural design of the buried pipe itself, BS EN 1295-1 and BS 9295 take over.

British Standards are only part of the picture. Sustainable drainage design in England works to CIRIA C753, the SuDS Manual, alongside the National Standards for SuDS and the SuDS discharge hierarchy those standards set, and off-mains foul drainage runs to BS 6297. Our free drainage calculators show the working against the standard behind each one, including a pipe gradient and fall calculator.

How to get a copy of BS EN 752

BS EN 752 is a paid standard. BSI sells it through BSI Knowledge and BSOL, and there is no free, lawful full-text version of it anywhere. The copies circulating on document-sharing sites are unauthorised, and most of them turn out on inspection to be the withdrawn 2008 edition or one of the 1990s parts rather than the current text.

What you want is BS EN 752:2017 incorporating the corrigenda of October 2019 and February 2022. A copy predating those corrections carries an uncorrected National Annex: the 2019 corrigendum fixed clause NA 6.4.1(a) and Figures NA.4 and NA.6, and the 2022 one corrected Table NA.5. If the reason for wanting the standard is a design rather than a management question, BS EN 16933-2 is more likely to be the document actually needed, and many organisations buy both. Universities, larger consultancies and some public libraries hold BSOL subscriptions that cover them. The NBS publication index is a free way to confirm which edition and amendments are current before you buy.

Standards say what a system has to achieve. Turning that into a scheme a council or a water company will accept is a separate exercise, and it is where most of the argument happens. If you need foul drainage design for your development, a surface water scheme prepared and defended through planning, or simply a straight answer on which document your site is being judged against, our drainage strategies for planning cover it. Call +44 (0) 1293 214444 or email enquiries@unda.co.uk and one of our experienced consultants will come back to you the same working day.

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