Utilities evidence where a main crosses the site

A water main or a public sewer crossing the site decides the layout before anyone draws a plot. Where a water main crosses the site, the evidence a planning authority wants is narrow and practical: the undertaker's asset records, the width of the protected corridor, and a written position on whether you are building over it, building near it, or paying to move it. Get that position in writing before the layout is fixed. Schemes that leave it to the discharge of conditions lose plots at the worst possible moment.

Finding the apparatus and its easement

Start with the statutory sewer map. Section 199 of the Water Industry Act 1991 requires every sewerage undertaker to keep records of public sewers, disposal mains and lateral drains, and an asset location search returns an extract of that map along with the water mains record. The two are usually separate datasets, so ask for both.

The map is a record of what the undertaker believes it owns. It is not a survey. Alignments drift, depths are often absent, and connections made over a century of piecemeal development rarely match the drawing.

Private drainage is the usual trap. Shared private sewers and lateral drains laid before 1 July 2011 transferred into public ownership under the 2011 adoption regulations, so a pipe serving more than one property will often be public even though nobody has ever treated it that way. If a run crosses your site and serves a neighbour, assume it is public until the undertaker says otherwise.

Then check the title. An easement granted by deed will be noted on the registered title and shown on the title plan, and the deed itself sets the corridor width and what you may and may not do inside it. Absence of a deed does not mean absence of rights. Undertakers hold statutory powers to lay and maintain apparatus, and older mains frequently sit on land where no express grant was ever registered.

Trial holes settle the argument. On any site where the corridor materially affects developable area, a short programme of hand-dug inspection pits along the recorded line is money well spent, and the findings sit comfortably alongside the other site information you are already gathering for ground parameters inside a Geotechnical Assessment.

Standoff distances and build over rules

Approved Document H to the Building Regulations deals with the point at H4. Building over, or within three metres of, a drain or sewer shown on the public sewer map requires the agreement of the sewerage undertaker, and that agreement is given through a build over or build near application. Three metres is a Building Regulations trigger, not a planning rule, and it is the figure most people have in mind when they talk about a standoff.

Water mains are different. There is no single national distance. The corridor comes from the easement deed where one exists, and otherwise from the undertaker's own standards, which scale with diameter, depth, material and pressure. A 90mm distribution main under a footpath and a strategic trunk main under a field are not the same constraint and should never be drawn the same way.

Undertakers will usually refuse to allow building over a rising main or a trunk main at all. Maintenance on a pressurised pipe is disruptive and urgent, and the asset protection team will not accept a dwelling sitting on top of it.

Diversion against design around

Section 185 of the Water Industry Act 1991 gives the owner or occupier of land a right to require the undertaker to alter or remove a relevant pipe. It is a real right, and undertakers do honour it. The qualifications matter though. You pay the full cost, the undertaker decides the engineering, and it may refuse where the alteration would damage the system or cause an interruption that cannot be managed.

A diversion also needs somewhere to go. If the new alignment leaves your ownership you need a third-party easement, which is a negotiation with a neighbour who has no reason to hurry. Diversions that stay within the red line are far quicker to agree.

Designing around the corridor is cheaper more often than developers expect. Put the protected strip under an access road, a parking court, a footpath link or an area of amenity grass, and the land does double duty. What you cannot do is bury the corridor under something you also need: an attenuation tank, a substation, a basement, or the one patch of the site where the levels work for a pumping station.

Programme and cost of a diversion agreement

Nobody publishes a national price. Undertakers quote individually and recover design, legal, construction and supervision costs, so budget all four rather than a single build figure, and ask for the current charging arrangements in writing at the enquiry stage. Treat early verbal figures as indicative.

Programme is the greater risk. A diversion runs through a technical enquiry, a quotation, acceptance, detailed design, legal documentation and then a construction slot in the undertaker's own work programme. Several of those stages sit entirely outside your control. Measure the sequence in months and ask the asset protection team for their published service standards at the point you first make contact.

And treat the planning programme separately. A diversion does not need to be complete before permission is granted. It needs to be deliverable, with a clear route from permission to a signed agreement.

Layout consequences of a protected corridor

The corridor rules out buildings and structural foundations. It also rules out, in most undertakers' standards, deep-rooted tree planting, substantial level changes, retaining structures and anything that obstructs plant access. Boundary walls crossing the line are usually permitted only with a lintel detail agreed in advance.

That has consequences you will feel in other documents. A strip of mown grass cannot carry the tree planting a landscape scheme assumed, which pushes canopy cover elsewhere and changes the habitat baseline feeding your biodiversity metric. Surface water design shifts too, because an infiltration basin sitting over a water main is not going to be accepted, a point worth settling alongside the climate change allowances in a drainage strategy.

Adoptable roads crossing apparatus need protection measures agreed with both the undertaker and the highway authority. That is two consultees with different programmes and no obligation to coordinate with each other.

Evidence for the application

The planning submission needs to show the authority that the constraint is known, mapped and resolvable. A proportionate pack is short.

1. A site layout plan with the recorded apparatus and the protected corridor drawn and labelled, not just mentioned in text.
2. The asset location search extract, dated, as an appendix.
3. Written confirmation from the undertaker's asset protection team of its in-principle position on build over, build near or diversion.
4. A drainage strategy that routes foul and surface water consistently with that position, and that does not quietly assume a connection point inside the corridor.
5. Where capacity rather than position is the issue, a foul sewage assessment with the undertaker's capacity response attached.

A short section in the covering statement tying those documents together saves the case officer from assembling the story themselves. The relevant supporting documents sit across the drainage and utilities categories in the full list of report types, and a drainage strategy is the one that most often carries the apparatus plan.

Conditions and informatives to expect

Expect an informative repeating the undertaker's standard advice about building over its apparatus. Informatives are not enforceable, and an informative is a reasonable outcome where the position is already agreed.

Where it is not agreed, authorities commonly impose a condition requiring details of foul and surface water drainage to be approved before development begins, and sometimes a Grampian condition requiring the diversion to be completed before occupation. A Grampian condition is only lawful where there is a reasonable prospect of the works being carried out within the life of the permission, so a diversion the undertaker has already refused in principle cannot be conditioned into existence.

Push back on conditions that restate the Building Regulations. A condition requiring a build over agreement duplicates a separate statutory control and fails the necessity test in national guidance on the use of planning conditions. Offer the case officer an informative instead and explain why.

This is general guidance, not legal advice; check the position with your local planning authority, the relevant undertaker or a qualified professional before relying on it.

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