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Build-Over Agreement

What is a build over agreement?
A build over agreement is a Water Authority seal of approval for the building work you plan to have carried out over or near a public sewer owned by them. It gives assurance that you have given the sewer the correct clearance from your new foundations. It also ensures that sufficient access to the sewer is maintained so they can clean or repair it if necessary. It also gives certainty of these facts to anyone looking to buy your property, should you come to sell. For more information on build over agreements please see the below answers from Thames Water:

How is ownership of drains and sewers determined?
The property starting the drain run is called the ‘head of the run’. This pipe is private. As soon as the pipe crosses the boundary into third party land it becomes a ‘lateral drain’. Once the second property connects into the lateral drain, the pipe becomes a ‘public sewer’. All sewers and lateral drains constructed before 1 July 2011 and which connect to our network are all part of the public sewerage network owned and maintained by Thames Water. There are different applications for different sizes of sewer. Class 1 160mm diameter or smaller (domestic/commercial) Class 2 160 - 375mm diameter Class 3 over 375mm diameter For all classes, except class 1 domestic, we will need to carry out a Closed Circuit Television (CCTV) survey before you begin work to ascertain whether any repair work is required. Another survey is required when your building is completed, to check the sewer has not been damaged. If you have not obtained our agreement, in certain circumstances, we may seek that you discontinue your works and the buildings erected over the public sewer may need to be taken down. We would encourage you to get in touch with us early on in the design process to avoid any delays or other problems.

Can I build over a manhole?
No, we do not allow internal manholes due to the increased risk of internal flooding and odour issues, even if double sealed covers are used. Manholes must be completely removed and piped through manholes should be reconstructed outside of your extension, either on the line of the sewer or offset and connected by a Y junction. If your application shows an internal manhole it will be refused.

How much does the application cost?
This depends on the size of the sewer and whether your property is residential or commercial. Diameter Property type Cost Class 1 Up to 160mm (6”) Residential £343 Up to 160mm (6”) Commercial £687 Class 2 160mm (6”) to 375mm (15”) inclusive Any £687 Class 3 Over 375mm (15”) inclusive Any £1,300* *There is also a legal fee involved in entering an agreement for very large sewers which is usually in the region of £500. If you apply online you can pay using your credit or debit card. If you apply by post you can send us a cheque payable to Thames Water Utilities Ltd with your application form. Please ensure the site address is written on the back of the cheque. You can also opt to pay by credit or debit card. We will then contact you to make payment over the phone.

What does the build over agreement fee cover?
For small sewers (160mm and smaller) The fee covers: • Processing your application • Technical reviews of your plans • Discussing and agreeing any design changes proposals • Working with your Local Authority within Building Regulations • Issuing your agreement • Registering the agreement to build over or close to the public sewer on our records
For mid sized sewers (160 – 375mm) and commercial properties. As above but with 2 CCTV surveys of the length of affected sewer. One before and one after your build.
For large sewers (375mm and larger) As above but with a lot more time required from our engineers and 2 surveys. This survey may be by CCTV or man entry which will be at significant extra cost.
We won’t know what is required until you make an application and we have seen your plans and the sewers involved

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