Build over shared drain advice

[Deleted member 281264]

Just been looking into getting a build over agreement with thames water and the rules are quite confusing

I have two drains in the garden the first close to the alleyway which is private and only a couple of feet deep and serves the house and then connects into the shared drain by the back door which is around 1.6m deep and less than 160mm diameter. The flow of the drains is to the right in the direction of kitchen > dining room and I assume we are the first house in line as we are end of terraced rows of 4

Our planned extension is 4m deep from the original house the full width of the garden. I'm thinking it should be possible to create a new manhole outside the extension with a Y junction. I'm just hoping TW won't refuse this and scupper my plans. Any help and advice much appreciated

 

[Deleted member 281264]

No one? lol

 

[sxturbo]

In Southend the water company won't let you build o er man holes and insist you move them.

If it was just pipes running under the. A build over agreement is offered and you use one of their approved sun contractors, along with the usual sign off.

I'm not sure what it's like in your local area.

Moving man holes is ruddy expensive

 

[Hugh Jaleak]

Really need a bit more info on where the drains currently run and where you want to build please. Unlikely they'll allow a chamber inside the footprint of the property, so you'd need to be planning straight runs under the building, then the chambers outside, but all runs will need to be accessible for clearance should the need arise.

 

[^woody^]

The cavalry has arrived.

 

[Deleted member 281264]

Really need a bit more info on where the drains currently run and where you want to build please. Unlikely they'll allow a chamber inside the footprint of the property, so you'd need to be planning straight runs under the building, then the chambers outside, but all runs will need to be accessible for clearance should the need arise.

The extension is planned 4m from original house then thames water require manhole to be 500cm from the building. I don't have any maps of how the drains run I hear they are hard to come by anyway. might be a case of not knowing until digging starts

thames water definitley won't allow manhole inside & wouldn't want to anyway. i'm quite lost when it comes to drainage but hoping the cost of moving it won't be more than £1200

 

[noseall]

Any help and advice much appreciated

6" common line built over - sorted.

Big Trench

• noseall
• 12 Jun 2020

 

[sxturbo]

I doubt £1200 would even dig the hole.

I wouldn't like to guess the cost but can guarantee £1200 is far to little.

You might want to get some costings before committing not budgets.

 

[sxturbo]

6" common line built over - sorted.

Big Trench

• noseall
• 12 Jun 2020

Yeah that's easy enough, but the op has 2x man holes..

 

[noseall]

We (naughtily) didn't bother getting a BOA, rather we just carried on as we would normally, i.e. removed all old clay pipe from beneath the extension and replaced with new plastic. This was facilitated with a new IC right on boundary (access). All was agreed and logged and photographed with the BCO.

The customer has been given retro permission since the extension was completed after paying for his own survey and sending it in to South Staffs Water. good job really.

However, with our site, there are neighbouring buildings built over the sewer BOTH sides of the boundary.

 

[noseall]

Yeah that's easy enough, but the op has 2x man holes..

Yes, and its a faff. Their oversite will look like a patchwork quilt and will likely require some metal fabric putting in the slab.

 

[Deleted member 281264]

6" common line built over - sorted.

Big Trench

• noseall
• 12 Jun 2020

Nice

I doubt £1200 would even dig the hole.

I wouldn't like to guess the cost but can guarantee £1200 is far to little.

You might want to get some costings before committing not budgets.

Why so much for a hole ? we are going to be digging foundations at least 1.5m anyway, then block and beam floor

 

[Hugh Jaleak]

Given the depth of some of the system, the excavations for the drainage will need shoring, if you're not sure where the drains run, then some exploratory digging may be required. Area will need to be surveyed for any other services, (gas/water/electricity), that may run through the excavations. Is there sufficient access to get machinery into the area? Space to put excavated material?

Thames may insist on a CCTV survey before and after, (then there's their fees to consider). Can you get a sufficient fall over the diversion route? Costs of new drainage materials, chambers, (again, depends on what Thames want), bedding material for pipework, backfill etc. It's not always that easy....

 

[Deleted member 281264]

Given the depth of some of the system, the excavations for the drainage will need shoring, if you're not sure where the drains run, then some exploratory digging may be required. Area will need to be surveyed for any other services, (gas/water/electricity), that may run through the excavations. Is there sufficient access to get machinery into the area? Space to put excavated material?

Thames may insist on a CCTV survey before and after, (then there's their fees to consider). Can you get a sufficient fall over the diversion route? Costs of new drainage materials, chambers, (again, depends on what Thames want), bedding material for pipework, backfill etc. It's not always that easy....

We have a garage that will be getting knocked down and an alleyway so should be plenty of access, I understand this is going to be a big cost which is why I'm trying to plan ahead a little

I think from reading thames water website they only insist on a drain survey with cctv for sewers over 160mm in diameter, this looks a fair bit smaller than that.