Thames Water Sewer Build Over:

When extending your home it is likely you will be building over or near public pipes or sewers that are hidden within your land.
It is important that public pipe work is protected at all times and that your build or extension isn’t going to hinder access to them.
You therefore may need to apply for a TW Build Over Agreement before you begin your work.

Thames Water build-over agreement

How do I know if I need to get Thames Water approval?

If you’re extending or adding to your house at all you will always need to find out if there are pipes/sewers under or nearby your site. If there are pipes within 3m of your proposal, you will need Thames Water approval.

How do I locate the pipes/sewers under my property?

First of all, try searching your property in this search engine: https://www.thameswater-propertysearches.co.uk/

The next option is to take a trip down to your local authority offices and having a look at their sewer maps.

If both of these methods aren’t successful, you’re going to have to get the professionals in and pay for a CCTV drainage survey. Expect to pay approx. £200 for this service. TIP: This is also a great opportunity to check the conditions of your sewer pipes!

How do I get approval?

You need to fill out an application form which can be found and uploaded here. Make sure you get your approval before you start laying your foundations to avoid fines or extra charges.

How long will my application take to be approved?

It shouldn’t take more than 21 days.

What sort of documents will I need for my application?

Your contact information

A cross sectional foundation plan (which can be provided by Aura Homes or your Structural Engineer)

A drawing of the pipe/sewer locations relative to both your existing property and your proposed work.

A copy of the drawings you submitted for your ‘Building Regulations’ approval.

Can I apply for a self-certified agreement?

To find out whether or not you are eligible for a self-certified agreement, fill in the questionnaire found here.

What is a self-certified agreement?

If you’re eligible for a self-certified agreement, all you need to do is fill out the online questionnaire and you may start your work immediately (providing your work complies with the description you gave in the online questionnaire).

A self-certified agreement is free of charge.

How much will my application cost if I’m not eligible for a self-certified agreement?

It depends on the size of your sewer.

If your sewer diameter is no more than 160mm, the application will cost you £299 (presumed domestic property).

If your sewer diameter is higher than this (which is unlikely in a residential project) expect a slightly higher cost.

If you have any further questions, get in touch. If we don’t know the answer.. we’ll know someone who will!

Ben Richards
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