TL;DR
A build-over agreement is Anglian Water's formal permission to construct an extension, conservatory, garage or similar structure over or close to a public sewer. As a general rule, any building work within around 3 metres of a public sewer needs Anglian Water's sign-off before you start, or you risk enforcement action and problems when you come to sell. If you're planning work near a sewer in Basildon or elsewhere in Essex and want help working out what's needed, get in touch online.
What a build-over agreement is, and why Anglian Water requires one
Anglian Water is the statutory sewerage undertaker for Basildon and the wider Essex region, which means it owns and maintains the public sewer network running beneath many residential streets and gardens. Under the Water Industry Act 1991, any new structure that would load, restrict access to, or risk damaging a public sewer needs the undertaker's consent first.
The agreement exists for three practical reasons: it protects the sewer from foundations or slabs that could crack or displace it; it preserves Anglian Water's right to get at the pipe for inspection, cleaning or emergency repair; and it creates a recorded consent you can show to conveyancers, mortgage lenders and future buyers, which avoids disputes further down the line.
How to find out if there's a sewer under or near your property
Many Basildon neighbourhoods — Pitsea, Laindon, Vange, Fryerns, Langdon Hills and Noak Bridge — were built during the post-war new-town expansion of the 1950s to 70s, and the standard practice at the time was to lay communal sewers in shallow trenches, often beneath rear gardens, driveways or side alleys. A meaningful share of properties in these areas have a public sewer running within a few metres of the house without the owner necessarily knowing it.
To find out whether a sewer affects your plans:
- **Check Anglian Water's online sewer map**, which lets you enter a postcode and view the recorded route of public sewers and lateral drains.
- **Request a formal sewer records search** if the map is inconclusive — Anglian Water can return a scaled plan showing the sewer's alignment, depth and easement.
- **Check your property deeds**, which sometimes reference a sewerage easement or wayleave, though not always precisely.
- **Arrange a site inspection** — a drainage contractor can look for surface clues such as manhole covers, inspection chambers or a change in ground level that suggests a sewer runs nearby.
If a sewer lies within roughly 3 metres of your proposed foundations, you'll need a build-over agreement before any work starts.
The general process
*The steps below describe the typical workflow. For current forms, fees and turnaround times, always check Anglian Water's own published build-over guidance, as these details are set and updated by them, not by us.*
Most homeowners start with a pre-application enquiry to Anglian Water's developer services team to confirm whether a full agreement is actually needed — some minor, non-structural works fall outside the requirement. A formal application then typically includes a scaled site plan showing the proposed structure and the sewer's location, details of the foundation design and materials, and any structural engineer's calculations demonstrating the load won't affect the sewer.
Anglian Water's engineering team reviews the submission and may approve it outright, ask for more information, or request an on-site assessment. Where a sewer runs directly beneath the proposed footprint, they will often ask for a CCTV drain survey to confirm the pipe's material, joint condition and any existing defects before granting consent. If agreement is given, it will set out specific conditions — such as minimum clearance from the pipe, protective measures like a reinforced slab or a load-distributing sleeve, and a requirement to keep manholes and inspection chambers accessible.
Throughout, Anglian Water is clear that the homeowner remains responsible for obtaining all necessary planning permission and Building Regulations approval separately — the build-over agreement sits alongside those, not in place of them.
Why a CCTV drain survey is often worth doing first
A CCTV drain survey — a waterproof camera fed into the sewer through an existing manhole or inspection chamber — is useful before you even apply. Sewer maps can be slightly out from the actual pipe route, especially where ground movement has shifted things over the decades, so a CCTV trace confirms the exact centreline and depth you need for accurate foundation clearances. It also reveals any existing defects, such as cracking or root intrusion, that Anglian Water may want addressed before permitting new load nearby. Submitting survey footage with your application demonstrates due diligence and can help the review move faster. Our CCTV drain survey service covers this kind of pre-application groundwork across Basildon, and where a survey turns up existing damage, our drain repair service can address it before you build. If you're buying a property and want to check for a nearby sewer before you exchange contracts rather than before you build, our pre-purchase CCTV drain survey covers that scenario too.
What happens if you build over a sewer without agreement
Building over or near a public sewer without Anglian Water's consent can leave you in breach of Building Regulations Part H4 and exposed to Anglian Water's rights over its apparatus, and the practical consequences can be significant. Anglian Water can require you to stop work, expose the sewer for inspection, and in some cases remove or alter the structure at your own expense. If unapproved foundations damage the sewer, you may be liable for the repair and any resulting flooding. Home insurance often excludes damage arising from unauthorised work over utilities, so a claim could be refused. And when you come to sell, conveyancers and mortgage lenders routinely check for a recorded build-over agreement — its absence can delay a sale or cause a buyer to walk away.
In short, a routine extension or garage becomes a real liability without consent in place first. Getting the agreement sorted before work starts protects both the sewer and your own investment.
If you're unsure whether a blockage rather than a build project is the issue, our guide to who's responsible for a blocked drain explains the difference between private drains, lateral drains and public sewers in more detail.
Get help before you start work
If you'd like help with a CCTV drain survey ahead of a build-over application, or want to understand what a specific Basildon property needs, get in touch online.
Frequently Asked Questions
**What is a build-over agreement?** It's Anglian Water's formal consent for building an extension, conservatory, garage or similar structure over or close to a public sewer, granted subject to conditions that protect the pipe and preserve the undertaker's access to it. The consent is recorded, and you'll usually need to show it to conveyancers, mortgage lenders or future buyers when the property is sold.
**Do I need permission to build over a sewer?** If any part of your proposed foundations or slab falls within roughly 3 metres of a public sewer, you'll generally need Anglian Water's agreement before starting work. Minor, non-structural features such as a shallow patio without foundations may fall outside the requirement, but it's worth confirming with Anglian Water directly rather than assuming.
**Who owns the sewer under my property?** In Basildon and across Essex, the public sewer network is owned and maintained by Anglian Water as the statutory sewerage undertaker, even where the pipe runs beneath private land such as your garden. This is separate from your private drain, which serves only your own property and remains your responsibility, and the lateral drain connecting it to the public sewer, most of which transferred into Anglian Water's ownership in 2011.
