Moving drains running near boundary

[SouthLondonCharlie]

Assuming my neighbour doesn't mind a bit of digging... I could try something like this:

 

[Hugh Jaleak]

Looking better, but rules used to demand a manhole at every change of direction in the drain, in which case you'd need 4, with the ones either end on the connections from and back into the existing run, in your neighbours gardens either side. You'd also need to accommodate a provision for access into the lateral serving the neighbours property, ideally a chamber on the junction into the main run.

Drainage regs seem to have been relaxed slightly now, so you might get away with a bit more than you used to, but ultimately it's Thames call.

 

[SouthLondonCharlie]

That's why I was a bit mystified by Thames's sketch in post #10 above from their official guidance - it shows two junctions without manholes. I've no idea what system of rules they work to but hopefully they'll give me a steer when they call back and not simply tell me to ask an engineer.

 

[Hugh Jaleak]

They do actually show an external rodding eye allowing access to the lateral in their diagram, the manhole gives downstream access to part of the main run, I would assume the first section including the junction would be able to be rodded from an upstream chamber. They do say 'Suitable external access must be maintained at all times.'

I would be working to a rule of thumb that all pipework must be accessible for rodding should the need ever arise. I would also be checking levels, and ascertaining you are still going to be able to achieve a suitable fall between the 2 points where you need to break into the existing drain, through the entire diversion, otherwise this job is going to be in trouble before you even start. You need an absolute minimum of a 1:100 constant fall, or you can forget any diversion I'm afraid.

 

[SouthLondonCharlie]

They do actually show an external rodding eye allowing access to the lateral in their diagram, the manhole gives downstream access to part of the main run, I would assume the first section including the junction would be able to be rodded from an upstream chamber. They do say 'Suitable external access must be maintained at all times.'

I would be working to a rule of thumb that all pipework must be accessible for rodding should the need ever arise. I would also be checking levels, and ascertaining you are still going to be able to achieve a suitable fall between the 2 points where you need to break into the existing drain, through the entire diversion, otherwise this job is going to be in trouble before you even start. You need an absolute minimum of a 1:100 constant fall, or you can forget any diversion I'm afraid.

Thanks, but rules of thumb & guesswork are only going to get me so far. Clearly I need to discuss with Thames Water what they think will work. Will report back if they get in touch.

 

[Hugh Jaleak]

You still need to check the levels Chap, if you don't know how to do it, I'd find someone who can. If you cant get a suitable fall between those 2 points, (i.e. it's already a very shallow fall over the existing straight run), you've no chance of diverting anything, and the whole idea is a non starter.

 

[SouthLondonCharlie]

I'm getting a drain survey first with invert levels marked on a plan so hopefully that will make it clear. Not sure who to use for this yet. If you can suggeest a reputable London company that does build-over surveys acceptable to architects then let me know!

 

[endecotp]

It's not hard to measure the levels with a couple of sticks and some hosepipe.

 

[SouthLondonCharlie]

Thames Water's build over team got back to me about this. It's good news as I can build over the sewer and don't need to re-route them. I just need to take out the existing manhole (making all the half-pipes inside into solid pipes) and then create a new manhole in my garden connected to the existing public sewer with a y-junction. This is to provide downstream rodding access. Thames never rod upstream so don't need access to the neighbour's drain or the junction that's currently under the manhole - they would be rodded from access points upstream. Building over the drains at 0.7m depth no problem either as I simply use concrete lintels to take the load where the wall passes over the drains.

So what seemed like a major problem turns out to be fairly trivial, though I need to budget for the manhole being moved and some expertise from an engineer regarding the lintels.