Build over agreement

10 Jun 2024
Reaction score
United Kingdom
Dear expert,

Any suggestions from the following response from Thames Water.
Bridge the sewer v1_032425.jpg
Your application was missing the following:

Sectional drawing showing proposed foundations and sewer(s)

Please confirm that the cross section provided is relevant to your build over as we cannot accept typical cross sections for both sewer.

A plan showing the foundation design in relation to the pipe to be built over showing:

• How you plan to bridge the sewer

• The use of a concrete lintel or steel beam

• At least 150mm of compressible material surrounding the pipe (e.g. pea shingle)

• Details of the invert level (depth) of the sewer.

• The clearance between either side of the pipe and the foundations.

Removing inspection chamber and replacing half pipe to full pipe

Since you are removing an internal inspection chamber, this should be done by removing the cover and frame first, removing the chamber walls and breaking out the benching and channel pipes carefully. The sewer should then be replaced using new pipes of the same material connected to the existing sewer appropriately. You will be required to manage the flows during this activity.
Manholes positioned on the public sewer
Since you are removing the existing manhole from the public sewer, we will require you to construct a new manhole in accordance with the design and construction guide. For more information, please review the Design and Construction Guidance.

How the public sewer enters your property.
From the plans you provided, it seems that your property's drainage system is private as it does not serve any other properties (and flows from your property towards the public sewer). Please confirm this.

If private, please confirm the distance of the lateral drain from the proposed foundation or extension.

If public, please show on your plan how the public sewer enters your property.
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I have submitted the above diagram for gap between foundation and both pipes. Do I need to submit anything else
I have submitted the above diagram for gap between foundation and both pipes. Do I need to submit anything else

Best ask Thames Water.

I found them more than helpful when we did our extension a few years ago. Far better than getting random advice off the internet

AND don't forget your BCO will need to see all the documents AND inspect the works as its undertaken
I have contacted them but they are very poor to answer any question. They would ask questions over email and response in 5 working days. Over phone it is difficult to get them to get advice
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The drawing does not comply with Thames' requirements for the reasons stated in their text.

It's also a poor design with higher risk of uneven settlement and movement.
Whoever drew the plans should be designing the arrangement around the pipes exactly as it will be on site.

Better to have the foundations closer to the pipes either side, and the bridging lower down closer to the pipes too.
Thank you for your suggestion.

The gap between two pipes are 100mm so I will filled with shingles.

Thames water specification suggests gap between foundation and pipe would be minimum 150mm if I am not wrong. Foundation can't be closer than it's requirement. Sewer pipe is 450mm below the ground level and rain surface water pipe is 350mm below the ground level.

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