Services / Build over agreements and drainage

Build over agreements and drainage

If your extension is over or near a public sewer, Thames Water must agree before you build. We check the sewer records, arrange CCTV surveys and prepare and manage the application.

FeesFixed fee for each stageagreed in writing before work starts

Request a fee proposal How our fees work

Build over agreements and drainage project, designed within the Green Code group

FreeInitial consultationA conversation about your project, and a first view of what's possible, before any fee is agreed.
FixedFee for each stageEvery stage is priced in writing before it starts. No hourly billing.
3DSee the design firstYour design is shown in 3D before it's submitted, while changes are still easy.
FreeResubmissionIf planning is refused, we revise and resubmit at no extra design fee. Conditions

What we do

Sewer and build over check
We check Thames Water's records to see whether a public sewer runs under or near the extension.
CCTV drainage survey
A camera survey to confirm the sewer's route, depth and condition, which Thames Water often asks for.
Build over application
Drawings and the application to Thames Water, managed through to approval.
Drainage layouts
New drainage for the extension, coordinated with the building regulations drawings.
Sewer diversions
Where building over isn't possible, drawings and coordination to divert the sewer.
Retrospective applications
Build over approval for work that has already been built, often needed before a sale.

Build over

What's included

Priced once we know whether a sewer is affected and what Thames Water will ask for.

Sewer record search and build over check
CCTV survey arranged where needed
Build over drawings coordinated with the structure
Application submitted and managed with Thames Water
Close-out at the end of construction

Before you start

What we need, and what sits outside our fee

From you: the property address, a few photos, and any existing drawings, planning approvals or surveys you have. We arrange the measured survey with you.
Not in our fee: council planning and building control fees, and specialist reports a council asks for, such as a tree survey or flood risk assessment, unless your fee proposal lists them.
Your fee proposal sets out exactly what is included for your project before any work starts.

Timescales

How long it takes

We give you a timetable for our work in your fee proposal. Council and other statutory timings start once an application is validated.

Sewer check: Before the building regulations drawings are finished
Thames Water review: Varies with the application; we apply as early as the design allows
Close-out: After the work is built, before completion

Common questions

When do I need a build over agreement?

When you build over or within 3 metres of a public sewer. Since 2011 many shared drains behind London houses are public sewers, so rear extensions are often affected even when the drain looks private.

Will Thames Water ask for a CCTV survey?

Often, yes, to confirm the sewer's route, depth and condition before and sometimes after the work.

Can I get approval after building?

Yes. A retrospective build over application can be made, and is often needed when a buyer's solicitor asks for it.

Other services

Where we work