Foul water sewer within boundaries of property

[StuckInARug]

Sorry I keep posting with lots of different questions on our house purchase - you’re all a lot more helpful and clear than our solicitors 🤣

surveys have come back indicating there is a foul water sewer within the boundaries of the property (Victorian semi), and that we should “contact the drainage company” if we want to know more! Who is even the drainage company? Is this something we need to investigate or just one of those things solicitors have to alert you to?

we do hope to extend a little bit into the garden in the future, if that makes any difference…

Drainage company would be your local water company ( or wastewater) is it something for your property or is it combined?

Most people have mains drainage on their property its how your foul water leaves

Do the mean you have shared waste drainage going through your garden? This is quite common on housing estates.(e.g. you have a waste water pipe leaving your property that joins onto the main sewer pipe, the main sewer pipe may run under the gardens on the estate with ech house on the estate attaching onto it in turn, as opposed to it running down the road)

You need to know that if it gets damaged at any point your garden may need to be dug up to repair it.

If you want to do an extension and the pipe goes under where you want to build I believe , depending on the water board, you may need to pay to have it re routed

The drainage company should provide a map to show where the pipe runs (some are notoriously inaccurate) although our solicitors have always got those fror us so id be a bit irritated at being expected to get it myself

As above. Also, make sure you don’t have any large trees anywhere near the line of the sewer either. It cost me £3000 to replace the sewer and re-lay the brick path on top of it, after my massive 40 year old flowering cherry tree rooted through it and broke the pipe!

Your local water and sewerage company (some areas it's 2 separate companies) will have plans of any part of the drainage system that they are responsible for.
Generally any drainage pipes that only take the waste from one house is the responsibility of the house owner. Anything sharing the drainage of 2 or more properties is the responsibility of the water company.

I’m assuming if they’ve flagged it then it’s a mains/trunk sewer rather than an individual drainage pipe running from the house to the trunk sewer. Other possibility is that it’s a shared waste pipe for you and a few other houses which then runs to the trunk sewer.

if it’s a trunk sewer you are unlikely to be able to build over the top of it, sometimes you can. But the local water company will tell you.

the thing about a pile which drains 2 or more properties being the responsibility of the water company is not always true, it depends on the age of the property as to whether it’s covered or not. The majority are actually the responsibility of the properties served by the sewers up to either where it joins the main sewer or to the boundary of the public highway.

I’ve seen the map now (it was with the conveyancing docs). I’ll try to post a pic, the house is the third of 4 semis (coming down the hill), so from what you’ve all said it’s probAbly the sewer from the top 2 houses that goes along the side of “our” house, down the back of the house and then joins across the back of the 4th house to join the road. On the map it says it’s not owned by Thames Water but it doesn’t say who it’s owned by! As far as I knew thames water owned all sewers in London?

my worry is that if it goes along the back of the house would that mean we can’t extend if we decide to? It’s hard to tell from the map but it looks like it’s maybe 3-4m away from the back of the house

Weirdly the section of the sewer that goes down the back of the 4th house IS owned by thames water according to the colour coding on the map! So it’s just the pipes on our garden that don’t seem to be owned by them!

Sounds a similar set up to my house. My neighbour built over his sewer (which runs into ours) with an extension. It means he can’t Rod his sewer out unless he comes in our garden.

my brother also built an extension over his sewer and he has an internal manhole in his extension. Sounds odd but if done properly it’s not an issue, it’s a special cover so very well sealed and no smells.

I live in a Victoria terrace. The main sewer for the road comes through the back gardens and responsibility for it is with the water board rather than householders I believe.

We have an extension and that stops about 2ft before it. That was built before we moved in.

Thames water will advise though. This link might be useful, it explains London sewer ownership. imperialdrainage.co.uk/blog/who-is-responsible-unblocking-drains-london/

looks like Thames water might be responsible for it according to that.

Actually, considering @QuebecBagnet ’s reply, it all makes sense. The sewer starts at our house so it’s not owned by the water company, but once it joins the 4th house (our downhill next door neighbours) then it becomes the water company’s as it will have the sewage of two properties. The semis uphill will probably connect to the main sewer before it gets to the house we’re buying

It’s definitely a trunk sewer not a main sewer.

This might help
From the ofwat web site

Our extension was built over the sewer, before we moved in. Another neighbour got permission to re route it.

As we’re end of terrace we also have mains sewer access in our front garden. It’s a covenant not to build over, or close to, that access point.

This is a common scenario, I wouldn’t worry too much.

That's a lateral sewer not a trunk sewer. If it only serves your property then you are responsible for it up to the point it joins a shared drain. If you didn't have sewers running through your garden where would your sewage go??

www.thameswater.co.uk/media-library/home/developers/larger-scale-developments/sewers-and-wastewater/build-over-or-near-a-sewer/building-over-or-near-a-public-sewer.pdf