Wrap-around Extension - Builder Over Agreement

3 Mar 2020
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United Kingdom
Hey folks, need your advice on a house I am wanting to put an offer on but would like some thoughts on whether my proposed wrap-around extension would have an approved builder over agreement (Thames Water) should I wish to change the location of the manhole cover/inspection chamber.

The property I am interested in is an end-terrace so I can benefit from a wrap-around extension.

However, I am aware, with Thames Water that the extension would cover the existing manhole cover and chamber.

Would my proposed diagrams work as illustrated in Diagram 2 (from Thames Water documentation)? I understand that the i'll have to incorporate foundations to the existing pipes and also the rerouted inspection chamber and connecting pipes.

Notes: the drains/sewers are shared and lateral to my knowledge.

Diagram 1
Build over agreement.png

Diagram 2
WhatsApp Image 2020-03-03 at 19.55.08.jpeg
Last edited:
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You would need something like this, but would require an existing manhole on the neighbours side for rodding and access. But whether Thames would agree to this is another matter.

foto_no_exif (2).jpg
I've updated my drawings to take into account the rodding eye.

Would this now work?
Build over agreement.png
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No. You can't lay drains out like that.

Would the new manhole and inspection chamber need to connect in the same direction (almost 45 degree angle) to the existing drain?

Like this?
Screenshot_20200305-074514_Autodesk SketchBook.jpg
Does it need to be a manhole in the green location? Wouldn't a rodding eye be just as suitable and less work?
I have no idea. I'm expert on this haha. Being end of terrace and I'm the only house with a manhole I think thameswater will force me to relocate it.

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