Drains/sewers

[From_a_different_time]

Afternoon all from a new member.

Looking to commission a small single storey extension on the back of a 1960s house. Technically, within Permitted Development.

This is the first time we’ve ever contemplated doing anything major to any house we’ve owned, so experience and naivety are polar opposites!

We have a sewer (adopted by the water company, so public) crossing to the rear of the house. On a slight angle; 3m out on one side, 2.6m out from the house on the other. Pipe size 100mm.

The question is simple but I bet the answers won’t be!

There is a choice to be made; is it common sense/the preferred option, for us to leave the sewer pipe where it is and build over (with approval) or should we be looking to do everything we can to have the sewer re-routed so that it doesn’t sit under the new extension?

Whatever we choose to do will have a significant impact on the size of the extension - hence cost.

We’ve been in touch with the water company who have been helpful.

The builder seems to prefer to move the sewer.

Just trying to understand the advantages/disadvantages of each.

Thanks for any input. Much appreciated.

Happy to provide more info if it helps.

 

 

[kandgmitchell]

How far out were you expecting to extend?

[markc]

Hi and welcome, a 4”” sewer won’t be from many or only one property so a move is not difficult at all. If it was a bigger one that would be a different matter altogether.

[kandgmitchell]

I'd say there's quite a lot of difference between diverting and building over.

 

Building over - depending on Water Company if you meet their standard criteria you may not have to contact them for a formal build-over agreement. Wessex for instance lists six criteria, meet them and you just carry on (subject to BC) keeping photographic records.

 

Diverting - you will need to submit a design, pay a fee, have the sewer CCTV'd before and after. Build manholes on the change of direction ensuring there is still enough fall between the two diversion points. Do it all within your property and have it inspected by the WC.

 

If the sewer is less than say 1.5m deep and you can extend to at least 500mm beyond the furthest point out from the house my vote would be for building over for simplicity ( assuming no internal manholes).

 

This is subject of course to the limited information provided.....

[From_a_different_time]

23 minutes ago, kandgmitchell said:

How far out were you expecting to extend?

To make the room useable, our ideal distance (outer wall) 2.9/3.0m from rear wall of house.

[From_a_different_time]

23 minutes ago, markc said:

Hi and welcome, a 4”” sewer won’t be from many or only one property so a move is not difficult at all. If it was a bigger one that would be a different matter altogether.

Thanks. We’re on a small estate. The sewer in our garden connects just 3 properties and we’re the middle one.

[From_a_different_time]

5 minutes ago, kandgmitchell said:

I'd say there's quite a lot of difference between diverting and building over.

 

Building over - depending on Water Company if you meet their standard criteria you may not have to contact them for a formal build-over agreement. Wessex for instance lists six criteria, meet them and you just carry on (subject to BC) keeping photographic records.

 

Diverting - you will need to submit a design, pay a fee, have the sewer CCTV'd before and after. Build manholes on the change of direction ensuring there is still enough fall between the two diversion points. Do it all within your property and have it inspected by the WC.

 

If the sewer is less than say 1.5m deep and you can extend to at least 500mm beyond the furthest point out from the house my vote would be for building over for simplicity ( assuming no internal manholes).

 

This is subject of course to the limited information provided.....

Thank you for the reply.

As far as we can see the major downside with building over the pipe is that with the clearance required from the edge of the new foundations, we’ll need the outer wall to be about 3.75/3.8m out from the rear wall of the house.

This is larger than we ideally want and the build cost will be far more than the initial quote we had from the builder which was for the outer wall of the extension to be 2.9m out from the house.

It’s only after receiving the initial quote that the potential issue with the sewer became apparent.

Of course, if we build over the existing pipe - and assuming the CCTV survey is clear and the pipe doesn’t need replacing  - then one benefit of this is that we wouldn’t run the risk of something going wrong and upsetting/causing grief, to our neighbours (drainage-wise).

No manhole located within the footprint of the new extension.

 

 

[kandgmitchell]

Presumably the diversion costs are less than adding a 0.75m-0.8m strip of extension to the build?

[From_a_different_time]

4 minutes ago, kandgmitchell said:

Presumably the diversion costs are less than adding a 0.75m-0.8m strip of extension to the build?

Currently waiting for a revised quote from the builder to confirm.

But in the meantime, just trying to understand how high the potential risks are when building over (sewer blockage, pipe failure, etc).

 

[kandgmitchell]

Done properly, making sure the pipe is protected and the foundations are kept clear and founded below then the pipe should be at no more risk than lying quietly in your garden. Hence why the likes of Wessex and other WCs regard these things as low risk.

[From_a_different_time]

44 minutes ago, kandgmitchell said:

Done properly, making sure the pipe is protected and the foundations are kept clear and founded below then the pipe should be at no more risk than lying quietly in your garden. Hence why the likes of Wessex and other WCs regard these things as low risk.

Thank you.

Never having had any building work done before now, I wasn’t sure if it was one of those situations where - faced with two options - one was clearly preferable to the other.

From our recent discussions, Severn T would, I believe, prefer a build over but also seem willing to consider a re-direct if that’s the only realistic option open to the property owner.