Cost and Complications from Drain Re-routing

[Pemu]

Good evening everyone,

I've just got hold of a drain map for the land I am considering purchasing. 

It shows there's a pipe running almost straight through the middle of the would be building. 

It's an end-of-terrace plot of land where the owners of the existing house is splitting the title and selling it after having obtained planning permission. 

We plan to explore the option of modifying the permission and including a basement and perhaps taking the ground floor out as close to the perimeter as possible . At the moment, there is a garage on top of where the drain is, which is to be demolished and replaced with the house. 

 

Based on this drain map, what problems and costs are now likely to arise as a result. 

For example, does that rule out a basement entirely, or mean we couldn't have one for the entire house footprint?

Would the drain need to be re-routed and if so, what kind of figures are we looking at?

Regardless of what we build, are we going to need to get some sort of clearances and permissions from Thames Water and what kind of costs is that likely to cause?

 

I'm attaching a picture of the block plan from the planning application to show the current planing permission and then the drain map. 

 

Ball park figures or anecdotal examples will be fine if more precise estimates are no possible, or at least pointers for where I need to be looking for further details. 

 

 

[joth]

If you haven't already, have a good read of 

https://developers.thameswater.co.uk/-/media/Site-Content/Developer-Services/Domestic-and-small-commercial/Building-near-pipes/Building-over-or-near-a-sewer/Building-over-or-near-a-sewer.pdf?la=en

It includes costs (page 3) and guidelines on when they can be moved -- both depend on the diameter of the sewer.  I'd be looking at getting a sewer survey done, and they surveyor might have some inside knowledge on it to.

A key point is whether this is a "new doweling" or alterations to an existing one.

 

Generally I'm told Thames Water aren't terrible to deal with, simply because so much of London is already built over sewers they have to deal with it all the time. But .... we haven't submitted our build-over application yet, ask me again in 6 months!!

 

 

[Pemu]

The placation says "New family dwelling". 

Is that likely to mean more or less cost. 

Will have a read of the above link in due course. 

 

By the way, what exactly is a sewer survey, how much does one cost and what are the benefits?

 

[Mr Punter]

You often get a key with the sewer plan showing the manhole depth and the pipe size and type. I doubt the one in the garden is more than 150mm diameter. Can you lift a lid and have a look?  It looks like you could just put in a couple more inspection chambers to re-route this and it should not cost a fortune.

[Oz07]

What about some water boards wanting 5m clearance to "sewers" wouldn't apply in this case due to current proximity to houses or small diameter of pipe?

[Pemu]

Evening everyone

I didn't have the whole document to hand previously and I do now. I'm attaching a larger picture and the key. The pip in questions doesn't have the diameter written next to it but a similar pipe in another part of the drawing is labelled 150mm. I don't have access to the land right now to check. 

Our current plan is to build a basement were the pipe currently runs, so we would need to reroute it closer to the boundary of the property, but it would still (according to our eventual plans) be underneath a singe story side extension. 

Does that sound like something Thames Water would likely be happy with and doesn't anyone have any rough idea of the costs involved with such a chance?

If that's hard to visualise, I can try to do a rough sketch.