Movong a manhole?

[fas496]

I am in the process of buying a house and plan to do a rear extension.
There is a manhole (shared sewer) which I believe will be very close the rear extension foundation; as close as half a meter. The drain from the manhole is connected to the sewer in the neighbour's property. Thames water owns the sewer and according to their
website, I will need their consent if the extension foundations are within 3 meter of the sewer. I have seen other forums saying that the foundations must be at least 0.6 meter away from the manhole?

Even if Thames Water allow me to move the manhole, I do not know if this will be feasible. I have these doubts (1) moving the manhole will involve moving the drains and the neighbour might object to this work entering their boundary. So this might be no-go then? (2) Anyone knows how expensive it could be to move the manhole altogether? A very expensive move will not justify extending or buying this property.

If I move the extension wall away from the manhole then the extension width might become so small that its unacceptable. I need to check the details for the plans.

Do I have other options? My aim is to make sure I understand my options fully before I complete.

 

[tony1851]

Although you have to obtain the company's approval, it should not be a technical problem.
When building close to a drain/inspection chamber, to comply with building regs, you usually take the foundation down to the level of the pipe.

 

[Newboy]

Too many variables to give you the answers you're looking for!

At this stage you can only be guided by the information provided by Thames water as it's their sewer.

I would expect that the sewer runs across the back of the property in which case you're going to need a build over agreement with Thames apart from any other consideration.
Are you sure that you're proposed extension will be permitted regardless of the sewer issues?

You post suggests that you have exchanged contracts in which case it's going to be expensive to pull out at this stage.

 

[fas496]

newboy, I have not exchanged yet but its getting too close now. You are correct in saying that I rely on information from TW to assess my chances. Unfortunately I do not think they will be much interested to pass on too much information without the £1300 planning application they want me to submit to analyse the case. Will the local building control office be able to help on this? All I have at this stage is a drainage map from the solicitor searches which shows this manhole at this property feeding into a neighbour's sewer and beyond. Looking at this I am assuming it takes foul water from the property I am purchasing to the sewer next door.

Do you see any obvious problems with the proposed extension? Its a semi so I will try to go the full 6 meters length if the neighbours do not object. As you can see the plot narrows going towards the back of the property and hence the irregular shape I envisage. I do not see anything wrong with this other than getting the related consents.

 

[theoldun]

With all due respect fellow, your drawing is as much use as a chocolate kettle.
The information required to be shown, are the existing house branch connections to the M/H. the inflow of the main drain into M/H, the outflow from M/H and depth of M/H.
Regards oldun

 

[maltaron]

If the manhole starts at your proposed property and then continues on then it is your property not the water authorities. Only if it carries more than one property does it become a sewer rather than a private drain.

 

[fas496]

I have spoken to TW and they are not sure the drainage plan they have given me is accurate. Their plan shows no inbound drains and an outbound one going to the neighbour's sewer. This makes it private on paper right?

How else can i check what inbound and outbound connections the m/h has? By physically inspecting the manhole?

 

[freddiemercurystwin]

Yes by looking, its the only way to know for sure, a bit of investigation is necessary, forget about the poxy maps that TW have on file, they're to be taken with a pinch of salt.

 

[fas496]

I went to have a look. Lifted the cover and this is what I see.



This is not a manhole is it? The downside it takes foul water from the neighbour next door, this property then passes onto the sewer next door.
Any thoughts?

 

[freddiemercurystwin]

When people talk of a manhole, we mean an access to a pipe junction under the ground, not necessarily something you can climb down. So yes in simple terms its a manhole. Anyway which way is that photo orientated on your diagram, because it doesn't seem to tally with it.

 

[noseall]

Do you see any obvious problems with the proposed extension?

Yeah, the 'orrible shape.

Are you aware of the problems associated with this i.e. obtuse brick corners and the issues regards roof water run-off etc?

Have you had a designer anywhere near your proposals yet?

 

[theoldun]

The three branch connections are from the house you are buying, the top inflow is from neighbours up line, outflow is to neighbours down line.
So this section pf drain is public sewer and under jurisdiction of water authority.
Regards oldun

 

[fas496]

Agreed oldun.

Thanks for the feedback so far. No I do not know about the drawbacks with obtuse corners and water run-off issues. Need to do more research on these. I have requested an architect to provide feedback re my high level plans so am awaiting that as well.

From my diagram, the picture of the sewer was taken when facing the fence and just outside the existing rear boundary window. The fence can be seen at the bottom of the picture

 

[noseall]

Water run-off issues would not be a problem with a flat roof, however....

 

[nickjb]

If I'm reading the orientation correctly the sewer is public and will run under the new extension. That means you'll need a build over agreement. It doesn't look that deep so your foundations will naturally be deeper but will require some extra complications and expense.

Can't see any other obvious issues. Looks like the existing house has an angled wall so no reason not to mimic that if you are happy with it.