What This Requirement Covers
Building over or close to a public sewer can damage the sewer, obstruct access for maintenance, and cause subsidence. Approved Document H4 and the sewerage company requirements govern what can be built over or near public sewers. A build-over agreement is typically required from the water and sewerage company.
Key Requirements
When a Build-Over Agreement Is Needed
- Building within 3 metres of a public sewer requires the sewerage company's approval
- Building directly over a public sewer requires a build-over agreement
- Some sewerage companies have different thresholds; always check with the local company
Conditions
Typical conditions in a build-over agreement include
- CCTV survey of the sewer before and after construction to confirm its condition
- Foundations designed to bridge over the sewer without loading it
- Adequate clearance between the foundation and the sewer (minimum 150 mm)
- No mechanical joints in the section of sewer under the building (if the sewer is old, it may need to be replaced with a modern pipe)
- Access for future maintenance must be maintained (manholes must remain accessible)
Design Considerations
- Foundations must be designed to span the sewer without imposing loads on it
- For strip foundations, the foundation may need to be deepened on one side and a lintel or beam used to bridge over the sewer
- For piled foundations, piles must be positioned clear of the sewer
- The structural engineer must account for the sewer's presence in the foundation design
Practical Compliance Tips
- Check for public sewers on the site before purchasing or before finalising the building layout; the water company's sewer records are available on request
- Apply for the build-over agreement early; processing times can be several weeks
- Commission the CCTV survey before starting foundation work; if the sewer is found to be defective, it may need repair at your cost
- Design foundations to bridge over the sewer with clear separation; do not build foundations directly on or against the sewer pipe
- Maintain access to all manholes within the building footprint (a manhole in a kitchen or utility room is acceptable with an appropriate cover)
- Keep the build-over agreement, CCTV reports, and foundation details for the building file
- Remember that public sewers adopted since 2011 include many former private drains; check the adoption status