ProjectCalcThe standard and its parts
BS EN 752 is the standard for drain and sewer systems outside buildings. Approved Document H cites it in parts, and the parts do different jobs:
- BS EN 752-3 — cited for sewer system planning, alongside Part 4 and Part 6.
- BS EN 752-4 — cited in full as "BS EN 752-4:1998 Drain and sewer systems outside buildings, Part 4 Hydraulic design and environmental aspects", and used for hydraulic design, with the relevant clauses being Clause 11 and National Annexes ND and NE in one place, and Clauses 3 to 12 with National Annexes NA, NB and ND to NI in another.
- BS EN 752-6 — cited in the guidance on pumps and pumping.
Approved Document H also notes that BS EN 752, together with BS EN 1295 and BS EN 1610, contains additional detailed information about design and construction.
When BS EN 752 takes over
The approved document is explicit about its own limits, and this is the useful part:
- Small catchments. The surface water section of Part H applies to drainage of small catchments with impervious areas up to 2 hectares. For systems serving larger catchments, reference should be made to BS EN 752-4.
- Larger soakaways. Soakaways serving larger areas should be designed in accordance with BS EN 752-4 or BRE Digest 365 Soakaway design — the assumed small-soakaway figure (10 mm in 5 minutes for areas of 25 m² or less) does not stretch to them.
- Flood risk. Where low levels of surface flooding could cause flooding of buildings, the design rainfall intensities should be obtained from BS EN 752-4 rather than from the document's own assumed figure.
- Stronger performance. The requirement can also be met by following the relevant recommendations of BS EN 752-4, so it is not only a fallback — it is an alternative route that gives the same outcome.
What the everyday numbers are, and where they come from
For a normal domestic job you never reach BS EN 752, because Part H's own numbers are enough: drains at least 75 mm diameter and surface water sewers serving more than one building at least 100 mm; 75 mm and 100 mm rainwater drains at not less than 1:100, 150 mm at 1:150 and 225 mm at 1:225; an assumed design rainfall intensity of 0.014 litres/second/m² for normal situations; and infiltration devices not within 5 m of a building or road. Those are on our Approved Document H page, with the paragraph references.
BS EN 752 is what a designer reaches for when the straightforward provisions run out: a catchment over 2 hectares, a soakaway serving a large area, or a site where a little surface flooding would reach a building. It is also the standard that deals with the things a small-job rule of thumb cannot — hydraulic capacity over time, environmental aspects, and the planning and maintenance of a system rather than a single pipe.
What this means for a calculation
The quantities our calculators produce — the gravel in a filter drain, the sub-base under a permeable surface, the volume of an infiltration trench — are materials estimates. The design of a drainage system, including whether it has enough capacity and where it may discharge, is a separate exercise that may be governed by BS EN 752. Getting the tonnage right does not make a system adequate, and an inadequate system is not fixed by ordering more gravel.
Edition status — what the approved document cites, and what is current
An approved document names the edition of a standard that existed when it was written. That edition is not necessarily the current one. The table below sets out, for every standard this page relies on, the title as published, the edition the approved document cites, and the edition BSI catalogues today (22 September 2026). Where the cited edition is withdrawn, the page says so; where we could not confirm the replacement, no current edition is stated.
| Standard | Title as published | Edition cited by the approved document | Current edition (BSI) |
|---|---|---|---|
| BS EN 752 | Drain and sewer systems outside buildings. Sewer system management | BS EN 752-4:1998 — cited by Approved Document H, which also cites BS EN 752 Parts 3 and 6 | BS EN 752:2017 — Current, Under Review (the part-numbered structure is gone) |
| BS EN 1295-1 | Structural design of buried pipelines under various conditions of loading — General requirements | BS EN 1295 — cited by Approved Document H with no edition given | BS EN 1295-1:2019 — Current |
| BS EN 1610 | Construction and testing of drains and sewers | BS EN 1610 — cited by Approved Document H with no edition given | BS EN 1610:2015 — Current, Under Review |
Source: BSI catalogue records read at knowledge.bsigroup.com on 22 September 2026. Each title, designation, status and date in the last two columns was read from the BSI catalogue page for that standard.
Last verified 22 September 2026. Every requirement quoted on this page was read from the primary source listed below on that date, not from a summary. If a figure could not be confirmed in the primary source it is not on this page.
Where these figures come from
- Approved Document H: Drainage and waste disposal, 2015 edition — BS EN 752-4:1998 citation and paragraphs 2.19, 3.1-3.2, 3.8-3.9, 3.30 and 3.36 — GOV.UK publications, "Drainage and waste disposal: Approved Document H", checked 22 September 2026.
- BSI catalogue (“BSI Knowledge”) — product record for each standard listed above: title, current edition and status — knowledge.bsigroup.com, checked 22 September 2026.
Guidance only, not advice
This page is a plain-English summary of published regulations and standards, written to help you plan a job. It is not professional advice, it is not a substitute for the actual document, and it is not a building-control decision.
Building regulations are enforced by your local authority (or an approved inspector) and the facts of a particular job can change the answer. Confirm with your local building control before you start work, and where a job is structural, get it designed by a suitably qualified person. If this page and the source document disagree, the source document wins.