Shared downpipe and ownership of sewer


30 Apr 2008
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United Kingdom
We live in semi-detached house with an inspection chamber for the rainwater sewer at the end of the garden with two inputs and one output.

The two inputs are fed by underground pipes from the rear of our house; the first fed by the downpipe from the garage roof and the second fed by the downpipe from the main house roof.

The guttering from the adjoining semi connects to ours and thus also feeds into this second downpipe so, as far as ownership and responsibility are concerned, does this mean that the underground pipe to the inspection chamber is considered a public sewer by virtue of it serving more than one property? There are no other underground connections.

The context of the question is that we are currently planning an extension to the rear of the house which will be within 3m of this underground pipe and therefore, if public, will require approval from the water authority and associated fees, inspections, etc.

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They say a picture is worth a thousand words so in case my first post was all a bit much here's a diagram:


Our property is the red one in the middle and the grey lines are the guttering and downpipes. The underground pipe of interest is the blue one, but I suppose the question is equally applicable to the pink one too given the shared garage guttering.

The proposed extension will occupy the same footprint as the existing conservatory.
I'm not 100% sure on this, but given the drain is for rainwater only and is only going to be a 4" pipe, I doubt anyone will get too worked up over it. I'd run the matter past Building Control before doing anything else, if they're happy to approve the matter without taking it further then so be it.

If the pipe was 6" or above, and/or carrying foul sewerage from a number of houses then I can understand Water Co. wanting to ensure it's protected correctly to avoid damage.
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Thank you both for the responses.

Hugh, the drain (which I think is indeed 4") eventually feeds in to the surface water sewer according to the plans (diagram updated). The foul drains/sewers are separate and around the front of the properties. I will be having BC involved and so perhaps they can give some advice as you say.

Daniel, that document was somewhat reassuring and does seem to suggest that the water company are able to take a pragmatic approach. I think my biggest concern was that my individual circumstances might not be taken into account and a fixed flowchart would be used to determine how much grief I am due! I also wondered if they could give any advice based on my somewhat crude drawing or whether I'd have to go the whole hog with a paid application.

We may well opt to remove the underground pipe next to the extension and divert the house downpipe round to feed into the extension downpipe instead. This would bring all the drains out into the garden thus facilitating much easier access should the need ever arise. Hopefully the water company might see this as an improvement compared to how things are currently.

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