Gas pipe and drains problem on a new extension

[Dave D]

Days before the building inspector comes ive found a problem.
We're knocking down an attached side garage and replacing it with an extension.
The Architect intended for the drains which run from back to front to be moved to go between the extension and side fence (they currently run uner the garage). Problem is ive discovered the incoming gas supply runs there already. SGN are coming monday to cut the gas off. The pipe seems to be steel all the way to the back of the house, where it must become yellow plastic. So the problem is obviously how can we get the waste water out to the front?
SGN have said they cant cut in to the steel pipe, which would have helped if done in the front garden.
I can think of 3 ways but not sure if they are possible. Or cost effective?
1) Use existing drains which run under the proposed extension. (house built about 55 yrs ago).
2) Install new drains where the old ones are. (under proposed extension)
3) See if theres another way of getting the gas in where it can stop at the front of the house. A new connection maybe.
Any ideas would be welcome. I'll attach a drawing to help.

 

[freddiemercurystwin]

How is the gas pipe in the way? What's wrong with option 2?

 

[Dave D]

How is the gas pipe in the way? What's wrong with option 2?

The intention and I would think quickest,easiest and cheapest way was for the drains to go down the side where the gas pipe is?

I presume option 2 - (new drains going under the extension) would be the most disruptive?

 

[bernardgreen]

SGN have said they cant cut in to the steel pipe, which would have helped if done in the front garden.

I would press them on that point, They will not ( or should not ) just cut the pipe and cap the end. Too much loss of gas and risk of a spark from the cutting tool igniting the escaping gas. If they can safely cut the gas off in the front garden then they can ( or should able to ) provide a means to re connect a new supply pipe in place of the cap when building work is completed.

 

[Dave D]

.

I would press them on that point, They will not ( or should not ) just cut the pipe and cap the end. Too much loss of gas and risk of a spark from the cutting tool igniting the escaping gas. If they can safely cut the gas off in the front garden then they can ( or should able to ) provide a means to re connect a new supply pipe in place of the cap when building work is completed.

Do you mean you think they can cut into steel pipe? Or they can turn ioff in the street?

 

[cdbe]

Have you checked the regs for distance required between gas pipe and drainage pipes? I don't think it's much - 250 or 350mm, so you should be able to fit both. Not that it matters but the gas pipe is probably plastic pulled through an old steel pipe.

I'm not sure of the complexity of running a new drain under the extension, probably not much and you can buy continuous 6m lengths of 110mm pipe so no joints.

I don't know why you want your gas supply cutting off?

 

[bernardgreen]

Do you mean you think they can cut into steel pipe?

Yes they can. A complex procedure using strap on gas tight adaptors allows for a hole to be drilled without any loss of gas and a balloon is then inserted into the pipe and inflated to block the pipe. The pipe can then be cut and capped. The balloon is then deflated and removed and its entry hole plugged.

These were taken when a leaky section of the gas main to the village was bypassed.

 

[Dave D]

Hello, I dont know how to quote small sections of text so ill try and answer questions below.

regarding getting the pipe and drain near each other, I would love to but the pipe will have gas in and its in the middle of a 1metre wide path, I doubt you can dig that close?
I want the gas off because the meter is on a wall in the garage thats coming down.

That strap looks interesting probably expensive but maybe cheaper in the long run?

I take it no one likes the idea of using the old drains?
cheers

 

[bernardgreen]

That strap looks interesting probably expensive but maybe cheaper in the long run?

The straps belong to the gas distributor. Definitely NOT a DIY item....

 

[Old Salt]

Rules for Cadent hopefully linked

https://cadentgas.com/nggdwsdev/media/Downloads/Pre-excavation-and-Ducting-Guide-January-2019.pdf

look at the section on specification for the trench which indicates 10 inches from drains. I cant see any other gas company having anything different.

If it was mine I would lay a new drain parallel to the gas main but keeping to the guidance provided by Cadent.

 

[mrrusty]

If it was me, and this is a private drain (i.e. no buildover agreement needed) I think I would install a new straight drain under the extension. The chances of a brand new straight drain with appropriate rodding access having problems in your lifetime are pretty minimal

 

[Dave D]

Thanks for your replies everyone. And for the link. I wonder if the 12 inches can be in any direction? IE if theres limited room but one is lower than the other so its diagonally 12 inches. It would mean digging by hand though I should think.

 

[noseall]

Any ideas would be welcome.

By the time you have dug the trench for the foundations, you will likely have loads of room to install your new drain along side the gas, in any case. Piece of pi$$.

As for cutting the gas off - whaa? Just work around it. Worse case, just crimp the yellow plastic with a clamp if you damage the gas.