building over sewer

[andrewf75]

Just found a minor unmapped (but now adopted) sewer running about 200mm out from the back wall of our proposed rear extension (parallel to the propsed line of the back wall) Just submitted a build over application to Thames Water. The sewer is 600mm deep so the foundations go below it, but the footings would be only 50mm from the pipe.

From the guidelines they seem to say that a clearance of 600mm is needed although I have read that this isn't always the case.

I assume they will come back and say we have to somehow bridge over the pipe, but presumably this will add extra costs? Anyone have an idea of what is likely to happen and how much it could cost?

Also the builders are on site already so we're a bit worried about delay. They have marked the application as urgent but how long is it realistically going to take?

Many thanks!

 

[DevilDamo]

It can take up to 28 days, but in most cases... is usually quicker provided they have all the correct information. Once the application is acknowledged, you should be given a contact name, number and reference, which will make it easier to chase up. But you can imagine the amount of "last minute" and "urgent" applications they deal with.

 

[andrewf75]

They called me today and gave a reference number and said up to 21 days. Yeah I can imagine they get a few urgent applications!

Any idea what they are likely to tell us we need to do in terms of foundations? Are we talking bridging over? Guessing we're probably looking at an extra grand or so on the building costs?

 

[ban-all-sheds]

Also the builders are on site already so we're a bit worried about delay.

But you knew about the sewer over a week ago, before the work started.

 

[DevilDamo]

Yes, they would probably ask you to provide min. 600mm either side of the sewer and lintel over it. It will probably add additional costs to the project but if you don't deal with it now, it will cost you more in the long run. The number of times I have dealt with Thames Water, I have never known them to refuse an application providing they have sufficient and correct details.

 

[andrewf75]

But you knew about the sewer over a week ago, before the work started.

we had an idea there was a sewer but thought it was a few metres further out. There was nothing suggesting it was going to be there at all. Only found out its position the day before.

 

[andrewf75]

Yes, they would probably ask you to provide min. 600mm either side of the sewer and lintel over it. It will probably add additional costs to the project but if you don't deal with it now, it will cost you more in the long run. The number of times I have dealt with Thames Water, I have never known them to refuse an application providing they have sufficient and correct details.

Thanks. So you mean we can keep the position of the rear wall of the extension as planned, but we need to somehow extend the foundations over the sewer?

 

[theoldun]

Yes, they would probably ask you to provide min. 600mm either side of the sewer and lintel over it. It will probably add additional costs to the project but if you don't deal with it now, it will cost you more in the long run. The number of times I have dealt with Thames Water, I have never known them to refuse an application providing they have sufficient and correct details.

Thanks. So you mean we can keep the position of the rear wall of the extension as planned, but we need to somehow extend the foundations over the sewer?

No. You are not doing a build over. A build over is where the sewer does cross the foundation between say 50 and 140 degrees.
You are building adjacent to a sewer that is running parallel to your rear wall and you must have at least 600mm clearance between foundation and sewer.
Also existing sewer must be vitrified clay.
Very much doubt whether Thames will give approval, but will tell you to either change size of extension or reroute drain
Regards oldun

 

[andrewf75]

No. You are not doing a build over. A build over is where the sewer does cross the foundation between say 50 and 140 degrees.
You are building adjacent to a sewer that is running parallel to your rear wall and you must have at least 600mm clearance between foundation and sewer.
Also existing sewer must be vitrified clay.
Very much doubt whether Thames will give approval, but will tell you to either change size of extension or reroute drain
Regards oldun

Well that would be a major spanner in the works. We could come in by 100mm or so, but any more wouldn't be worth it. Next door have built right up to it admittedly before the change of ownership, but surely they can come up with something?

 

[andrewf75]

oldun - or anyone else,
Do you have an idea of what it might cost to reroute the drain? are we talking thousands here?
or given that its a minor one is it possible they will allow our builders to put two bends in it (and presumably manholes) and move it back a metre?
Cheers.

 

[theoldun]

oldun - or anyone else,
Do you have an idea of what it might cost to reroute the drain? are we talking thousands here?

Can not give you a budget without more information, as their are so many variable factors that we do not know
Any way nine times out of ten, Thames water will only allow their own contractors to reroute a sewer They will provide you with a quotation, but knowing that band of sharp shooters, it begs she question, how long is a piece of string.
As stated previously Thames Water does not allow plastic pipe on a reroute of salt glazed sewer. They normally require Hep sleeve or Hep seal vitrified clay. Suggest you put it out of your mind until Thames Water come back to you.
Regards oldun. .

 

[andrewf75]

Thanks,
Yeah will try to put it out of my mind. Guess we will have to lose a bit of space, just hope they won't insist on the full 600mm from footings. If they let us go 300mm or 400mm away we can live with that.

 

[andrewf75]

got the go ahead to build 100mm from the sewer. Thames Water were very helpful and obviously don't stick to the 600mm guidelines...

 

[ban-all-sheds]

Interesting that they told me that I can't go closer than 300mm to the inspection chamber.....

 

[andrewf75]

Interesting that they told me that I can't go closer than 300mm to the inspection chamber.....

its 100mm from the pipe we are not building close to the inspection chamber