Build over and diversion agreements

Building over a public sewer

If you’re planning to improve your home by extending it, adding a conservatory, annexe or garage, it’s likely you will need to consider the existing drainage pipes within your land. As well as checking the local authority’s building regulations, it’s important you work with the local water authority (to make sure the pipework is protected and that their access isn’t restricted if they needed to service, maintain or replace any existing pipelines. Our coverage of the UK means we work with Thames Water, Anglian Water and Southern Water.

It’s best to know where the pipes are when you’re planning your work to help avoid delays and additional cost. Don’t worry if you’re not sure how to do this as we can help – Premier Drainage Solutions are an approved contractor, so we are able to provide objective advice and also carry out the works themselves, too.

Remember, if you’re building within three metres of a public sewer, or within one metre of a public lateral drain, you’ll need approval before work begins.

Build Over and Diversions FAQs

Diverting a public sewer

Developers with an interest in land that contains a public sewer can request the diversion of that sewer to allow development work to progress, in accordance with section 185 of the Water Industry Act 1991. If it’s a strategic sewer that’s being diverted, then you will need an approved contractor to carry out the work.

Step 1 - Submit your application

This should include the design and specification for the diversion, confirming the type and location of the sewer, as well as its ownership. It is good practice to have a drawing of the existing sewer with the new development (outline) drawn over the top, and a separate drawing showing the new diversion around the development.

Step 2 - Technical review

A technical review takes place to determine if the sewer is strategic in nature.

Step 3 - The decision

Around 14 working days after receiving the application, the local water authority (Thames Water, Southern Water or Anglian Water) will let you know if they need any more information. Once they have everything, within 28 days they will send you their technical decision and what you need to do next

Step 4 - Legal agreement

If the work is approved, you’ll need to sign the legal agreements that need to be in place before work on the sewer(s) can start.

Step 5 - Set the date

Here, you notify the water authority as to when the diversion is due to take place.

Step 6 - Inspection

Thames Water, Southern Water or Anglian Water (depending on your location) will send a field engineer on dates agreed and booked by Premier Drainage Solutions so they can inspect the works and advise any corrective actions required.

Step 7 - Sign off

When we have finished, we provide as-built drawings and CCTV surveys to your water authority (Thames Water, Southern Water or Anglian Water) so that they can update their records and ensure the construction has been carried out satisfactorily.

Step 8 - Certificate

Once work has been completed, the water authority (Thames Water, Southern Water or Anglian Water) will issue a provisional vesting certificate.

Step 9 - Final completion

After a one-year maintenance period, a final inspection check will be carried out. This is when the water authority will issue a final completion certificate and adopt (take responsibility for) the sewer(s).

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