Help understanding drainage search map

with effect from Oct 2011 the rules changed so the distinction between "sewer" and "drain" no longer matters the way it used to

the rules now are
- if the pipe transports flow coming from your property only then it is a "private drain" and any problem with it (blockage, collapse etc) is the responsibility of the householder to pay for

- if the pipe carries flow from more than just your property then it is the responsibility of Thames Water in your case.


hence on the image you show blue denotes pipes that the householder is responsible for and red denotes TW responsibilities since the latter serve more than one property. So where a blue pipe turns red from that point onward it is TW's responsibility.

concern yourself only with the pipes within the boundary lines of the property you are buying. Anything outside that boundary is not your responsibility and can be ignored.

Although it is not clear which of the properties on the image is the one you are buying a (blue) pipe coming from a house cannot join a red pipe unless there is a manhole. The only possible instance where there is no manhole in "your" garden would be if you were the very first (blue) pipe of the run - in which case the manhole for "you" may be next door and any blockage of your pipe would be dealt with by rodding back from "their" manhole to you, ie there would be a junction of red and blue next door

mrporkchop wrote: »

00ec25 thank you for your detailed reply. I've now marked 'my' house with a green star.

the red "dot" should (!) be a manhole otherwise the junction of your pipe with the TW pipe is impossible. Could the current owners have used one of the manhole covers you grow grass on to disguise it? Pot plant in the way? Under a bush?

similarly the blue dot implies there should be a manhole where the pipe(s) come out of your house and join to form the single pipe heading down the garden to join the red one

building regulations have required for a very long time that manholes are installed where pipes join or have a significant change of direction

mrporkchop wrote: »

Since only 3 of the 20 houses on the terrace appear to have blue lines and dots in their gardens, does this suggest that the other properties' drains are simply not marked on the plan (the plan doesn't seem to show how other houses on the terrace connect to the red pipe which traverses all of the gardens)? If neighbouring houses' drains connected to the blue drain in 'my' garden, it should therefore be 'red', ie owned by the water company?

before the rules changed all pipes within the boundary of a property were the responsibility of the property, and unless it was an ex council estate, such pipes would not always have been mapped on to a "drain" map as the water board did not care about them. The fact blue pipes are "missing" is therefore entirely unremarkable.

the fact the red pipe runs parallel with the building line across the gardens strongly suggests each property connects to it individually within the boundaries of their own garden. Your blue pipe is likely to be yours alone.

mrporkchop wrote: »

We had intended at some point in the future to do an extension which would cover the blue dot and line; if it was a 'private' drain would permissions from the water company still be required?

if it is foul (ie toilet) or grey (ie kitchen waste or sink/bath water) drainage, then building regulations will not allow you to have a manhole inside a building. You would have to change the entire pipe design or move the pipe. That is not an issue for TW, it is an issue for your local council when they approve your plans as being building reg compliant. You will need council BR approval even if you don't need council planning permission for the extension.

Sounds like you need to instruct your surveyor to very carefully check the drains plan and make sense of it against the actuality on the ground. Then ask him to advise on your extension options. Of course he may charge extra for such extra advice, but it sounds like it could be a deal breaker for you so spend the money now and make sure...

You can move an inspection chamber to enable an extension.

I just did!

martindow wrote: »

But if the extension goes over a shared sewer you would need to get permission from Thames Water to build it. If they allow it they would stipulate the construction needed over the pipe adding to the expense.

True, but it does look as if filling-in the side return here would be possible without involving anyone else's sewer directly.

If something altogether more ambitious is planned, it does look risky, especially as it's not just building over the shared sewer that counts, but also foundation proximity to it. Forgotten the exact distance.

But how many people do more than a side return extension on this sort of house? Other factors, like loss of light, come into play.