Building over public sewer - extension

Sanoffo

I spoke to Thames Water today about options for building over a public sewer whilst making it accessible from the outside of the new extension (so it can be sealed inside).

They said this could be achieved by putting in a new inspection chamber outside of the extension (at least 600mm from foundations) and connect a 'Y' junction, making sure the sewer runs it's course.

I'm still a little baffled by what they mean here and trying to work out costs at the same time. I would have thought a simple Y junction was enough to allow rodding access rather than a whole new inspection chamber to go with it?

I have drawn an image to describe what I think they meant...
http://s11.postimg.org/ff730cor7/drains.png

Has anyone had experience building over public sewers? Any ideas on pricing this up?

Thanks for any help in advance

Doozergirl

Your drawing makes little sense to me. Is it bird's eye view? Where is the extension?

If the layout is what I think it is, I don't think that is what they meant. It wouldn't work correctly, you need to work on the 'flow of poo' line.

I'm amused by the 'flow of poo' marker

What kind of drain is there at the moment? A manhole where the junction from your house meets the sewer?

PasturesNew

I once saw a price for moving such a pipe ... I think, from memory, it was over £26k.

Maybe they mean two Ys? One before the extension to take the pipe away from the building, then a straight stretch, then another Y to bring it back to the original pipe.

I am not going to draw a diagram ....

Doozergirl

It's not going to cost £26k, PN. You get to do this work yourself. If a utility provider was doing it, the sky is the limit for them. You have a digger in already, so cost is more likely to be around £1000 for a new inspection chamber and connections.

Two Ys would divert, but you don't usually need to divert. A replacement access, on the same line is their preference.

The word 'drain' is a bit confusing as really we need to know what is currently sitting in the area of the new extension to know what needs to be moved and replaced. 'Drain' is a very generic term.

PasturesNew

Doozergirl wrote: »

It's not going to cost £26k, PN. You get to do this work yourself. If a utility provider was doing it, the sky is the limit for them. You have a digger in already, so cost is more likely to be around £1000 for a new inspection chamber and connections.

Two Ys would divert, but you don't usually need to divert. A replacement access, on the same line is their preference.

The word 'drain' is a bit confusing as really we need to know what is currently sitting in the area of the new extension to know what needs to be moved and replaced. 'Drain' is a very generic term.

Cheers, that's good to know. I like to collect "random facts" so will now amend my previous random fact with your data

I think my previous info was more "mains sewer" than just "drain".

Doozergirl

That could make more sense. They're not going to let just anyone punch a hole in the side of the mains sewer. At that price, you'd go off grid, as it were.

PasturesNew

Doozergirl wrote: »

That could make more sense. They're not going to let just anyone punch a hole in the side of the mains sewer. At that price, you'd go off grid, as it were.

I think it was a small building plot, where it'd need moving to plonk a small house down. I read it on the details on RM, where they gave the quote/cost as part of the listing.

Sanoffo

I have another poo diagram!

Yes Doozegirl, by drain I mean inspection chamber and it is not a mains sewer. Thames Water did say there was no need to divert but I am still confused whether the flow will still run it's natural course or if it has to go through the 'new' inspection chamber. I have drawn how I imagine it to work again with the Y junction in the new chamber...



I'm also baffled that a new inspection chamber is even necessary if all they need is rodding access.

Thanks for the helpful advice so far!

Doozergirl

Hmm. Are you in a terrace and building full width?

I'm a bit baffled, to be perfectly honest. I'm not going to pretend I know what they're talking about either. . I'm really sorry. All of my build over experience is with semi or detached houses, meaning we have space on at least one side to put a new inspection chamber.

I'll look for some technical guidance for you, but I would ask my building control officer for help, in your situation.

Doozergirl

Clear as mud, I'm afraid. Can't find technical for Thames water, but the wording is similar to ST, here:

http://www.stwater.co.uk/upload/pdf/guidance_notes.pdf

New access chamber on the line of the poo flow or a total diversion. No diagrams as pretty as yours.

Another phone call to Thames Water, maybe, with your nice picture emailed to the person on the phone?

Sanoffo

Yes, building full-width. I will call Thames Water again tomorrow, thanks

I was hoping we could just branch into the existing inspection chamber/pipeline and have a gully in the garden for rodding access - like so: