Documents for a site crossed by a public sewer
A public sewer imposes a consenting process that runs alongside planning on its own timetable. What to order, what to show and when to start the agreement.
A public sewer crossing the site is not a planning constraint in the ordinary sense. The council will not refuse permission because of it, and the undertaker is not a statutory consultee on most applications. What the sewer does is impose a parallel consenting process, under water legislation rather than planning legislation, that runs on its own timetable and can stop a scheme being built exactly as approved.
So the documents you need fall into two groups. The evidence that goes into the planning application, and the evidence the undertaker needs before it will agree to a build over or a diversion.
Establishing the route and the status of the pipe
Order the sewer records before the layout is drawn. The undertaker maintains a map of its public sewers, and an asset location search will show what it believes it owns.
Then treat that map with suspicion, for one specific reason. Sewers serving more than one property transferred into public ownership in 2011, and many of those pipes were never accurately surveyed. A drain shown as private, or not shown at all, may now be a public sewer, and the discovery usually happens when a trench is opened.
Where the records are thin, commission a drainage survey. A CCTV survey with a topographic tie-in gives you the line, the depth, the diameter, the material and the condition, and you will need that information later for the agreement in any case. The process for obtaining records is covered in the note on ordering sewer records and pre-development enquiries.
Check the status of each pipe separately. A public sewer, a lateral drain, a rising main and a private drain attract different rules, and rising mains in particular are treated far more strictly than gravity sewers.
Easement widths and what they prevent
Undertakers protect a strip of land either side of the pipe. The width is set by the undertaker's own standards and increases with the diameter and depth of the sewer, and a common starting point for a small gravity sewer is a few metres either side of the centre line.
Inside that strip, expect restrictions on building, on tree planting, on deep-rooting landscaping, on significant level changes and on anything that prevents access for maintenance plant.
That has a real effect on the layout. An easement running diagonally across a site can remove more developable area than its width suggests, because it fragments the plots either side. Draw it first, at the correct width, and design around it rather than discovering it at technical approval.
The strip is not wasted land. It usually works as access road, parking, amenity grass or part of a drainage feature. What it will not do is carry the tree planting a landscape condition might otherwise expect, which is worth flagging in the planning submission so that the landscape scheme and the drainage layout do not contradict each other.
Build over and build near agreements
Where a building will sit over or close to a public sewer, the undertaker's consent is needed under a build over or build near agreement. That consent is separate from planning permission and separate from Building Regulations approval, and it is refused often enough to be a real programme risk.
What the undertaker will want to see, broadly, is this.
- A location plan and a detailed drawing showing the proposed structure against the surveyed sewer line and depth.
- A CCTV survey confirming the condition of the pipe before works start.
- Structural details of the foundation solution, commonly a lintel, a raft or a piled arrangement spanning the pipe.
- A method statement covering excavation, protection and working near the asset.
- Confirmation that access for maintenance is preserved, including manhole positions.
Approval is discretionary. Large trunk sewers, rising mains, brick sewers in poor condition and sewers at significant depth are frequently excluded from build over entirely, and the answer is a diversion or a redesign. The detail of what the agreement covers is set out in the note on building over or near a public sewer.
Diversion and its timetable
Where the sewer cannot stay where it is, the Water Industry Act 1991 provides a route for a developer to require the undertaker to divert a public sewer to enable development, at the developer's cost.
The cost is the obvious part. The timetable is the part that damages programmes. A diversion involves design, agreement of the new route, land rights over any third party land, an easement, construction and adoption, and it is measured in months rather than weeks.
Start the conversation before the planning application is submitted, not after permission is granted. Two things follow from that. The layout can be drawn around the diverted line rather than the existing one, and the planning submission can explain the position rather than leaving a contradiction between the approved layout and what will be built.
Where the diversion cannot be completed before development starts, expect the council to impose a condition preventing occupation, or particular phases, until the works are complete. That is a normal outcome and it is easier to accept when proposed rather than imposed.
What goes into the planning application
The sewer itself rarely needs its own report. It appears across several.
The drainage strategy should show the existing sewer, the easement, the proposed connection point and any diversion, with the discharge rate and attenuation unaffected by the constraint. The foul sewage assessment should record the capacity position and the undertaker's response to the pre-development enquiry. And the utilities assessment should carry the wider picture of apparatus and lead times, so an officer can see how the pieces fit.
Show the easement on the submitted layout plan rather than only on a drainage drawing. Officers approve the layout plan, and a plan that omits a constraint you already know about creates an inconsistency that has to be resolved by amendment later.
Programming the agreement against the consent
The sequencing that works is simple and it is regularly ignored.
Records and survey at feasibility. Pre-development enquiry and a preliminary view on build over or diversion before the layout is fixed. Planning application submitted with the constraint shown and the intended solution described. Formal agreement or diversion progressed in parallel with the determination period, not afterwards.
Where a scheme is being sold on with the benefit of permission, the state of the sewer agreement is one of the first things a purchaser's technical due diligence looks at. A permission with an unresolved build over question is worth less than one where the agreement is in place, and the difference is usually larger than the cost of sorting it out.
This is general guidance, not legal advice. Easement widths, build over policies and diversion procedures vary between undertakers, so check the position with the relevant water company, your local planning authority or a qualified professional before relying on it.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
How do I find out where the public sewers are?
Order an asset location search from the undertaker, which shows what it believes it owns. Then verify it. Sewers serving more than one property transferred into public ownership in 2011 and many were never accurately surveyed, so a pipe shown as private, or not shown at all, may now be public. A CCTV survey with a topographic tie-in settles it.
How close to a public sewer can I build?
The protected strip is set by the undertaker's own standards and widens with the diameter and depth of the pipe, with a few metres either side of the centre line being a common starting point for a small gravity sewer. Inside it, expect restrictions on building, tree planting, level changes and anything blocking maintenance access.
Is a build over agreement the same as planning permission?
No. It is a separate consent from the water undertaker, distinct from planning permission and from Building Regulations approval, and it is discretionary. Trunk sewers, rising mains, brick sewers in poor condition and deep sewers are often excluded from build over entirely, in which case diversion or redesign is the only route.
Can I make the water company move a sewer?
The Water Industry Act 1991 provides a route for a developer to require the diversion of a public sewer to enable development, at the developer's cost. The cost is predictable. The timetable is the risk, because design, route agreement, land rights, construction and adoption are measured in months rather than weeks.
Should the easement be shown on the planning layout?
Yes, on the submitted layout plan rather than only on a drainage drawing. Officers approve the layout plan, and a plan that omits a constraint you already know about creates an inconsistency that has to be corrected by amendment later. Drawing it at the correct width early also prevents a layout that cannot be built.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.