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.
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!
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.
It shouldn’t take more than 21 days.
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.
To find out whether or not you are eligible for a self-certified agreement, fill in the questionnaire found here.
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.
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.