Help required - build over agreement "refused"

28 Dec 2021
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United Kingdom
hi everyone,

the only thing we're missing in order to start out rear extension project is a build over agreement. we applied on time and as promised, thames water responded fairly quickly. unfortunately, the answer was not positive and I'm not sure how to proceed.

Screenshot 2022-06-21 at 18.30.46.png

long story short, we have two manholes in our rear garden, as can be seen above (right). the first manhole, close to the house, takes all our drains along with rainwater from the neighbour (which is in fact our rainwater, as we share the guttering). the second manhole takes the entire content of the first manhole along with a lateral drain from the same neighbour. from there, it goes into the main sewer at the back of the house.

I proposed that we get rid of the first manhole, all the pipes will be re-routed as part of the extension works anyway, to be captured by a new manhole just outside the extension and to feed straight into the second manhole, which will remain in exactly the same position. I also proposed that we redirect that rainwater pipe directly into the same second manhole. this is what thames water came back with:

  • Thames Water do not allow bends under buildings, unless you can provide a new man hole on the sewer at the rear and confirmation of an external man hole on the existing sewer run in a neighbouring property (on the section of pipe work that has the bend on it). This is so we are able to rod the sewer from both directions in case of a blockage. Please update your plan accordingly.
can anyone explain what they want and what the best way to proceed is? builder and neighbours are flexible, I just need something that works. I was convinced that bends in sewers are allowed and the whole argument that rodding won't be possible is simply non-sense, as they're flexible. it's a large angle bend, so easily accessible from the existing manhole.

any help?

thank you
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They want another manhole as per red below, and on the sewer.

There’s already a manhole there, the neighbour has it!!!

Does that mean if I inform them of it, it’s all good?
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And the planning permission you forgot
Oh no, planning permission, party wall agreements, structural calculations and restrictive covenant relaxations are long done. The only thing missing was the build over agreement, which was meant to arrive this week.
That's what they are asking for, confirmation. And a new one on the sewer itself.
Sorry, what do you mean by a new one on the sewer itself? Both manholes (mine and the neighbour’s) remain where they are, rodding will be poasible from both directions.

What exactly is “the sewer” in this case and what new manhole will required?
Not according to you

I just realised we’re about to start works in a week or two and we have a terraced house, but our extension is 4m deep.

Building control is ok with our application (building notice), neighbour is ok with the works proposed (party wall), thames water is ok with the drainage (build over agreement).

How much trouble am I in without the prior approval?
I applied, it’s just a formality, will get done. It’s not planning permission I’m worried about, even a full application.
Presumably the one marked sewer on the drawing, where the drain connects to it.
But that aecond manhole remains. Why would I need a new one behind the existing one? You open the exiating manhole, rod the pipe and that’s it.

I’ll phone them up tomorrow and clarify.
You're asking to swap an existing chamber for a bend, buried under a building, I can see why they're not happy. Drain Rods will not go around a bend, so they want access to a straight run either side of the bend. Currently you could rod upstream to the bend from the chamber remaining in your property, if there's access to the downstream run from a chamber in the neighbours garden then they may be ok with it.
I don’t get it, what’s wrong with rodding from the second manhole that remains in place? Could you possible mark on the map where this new manhole ahould be?

I have a feeling whatever happens, it will be behind the existing one, which makes it obsolete, given the existing is public and thames water can access it anytime.
I did a bit of research. Are the things in my garden inspection chambers and not manholes? Does that mean I have to add a rodding eye/manhole between the extension and the inspection chamber?

I always thought rodding is done with a flexible metal hose that rotates, clearing the blockage.
It's pretty clear to me what they are asking for. Better to call them and discuss if you aren't sure.

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