Risks - Building Extension Wall Over Sewer

[nickldn]

I am in the process of building a 3m extension at the back of the house and as luck would have it a sewer serving 6 houses is running 3m behind the house, right where the back wall of the extension is planned. The minor sewer runs around 1.2m below ground.

I have obtained a build over agreement from Thames Water and the architect has specified pad and beam foundations to support the back wall.

The question is should I really be building the back wall of an extension directly above a sewer. What would happen if the sewer needed to be repaired?

It's all well and good having to make a hole in the kitchen floor to fix a sewer pipe, but what about if a wall is directly on top of the pipe? Does that make it more likely the sewer could be repaired from the outside of the extension, or would it mean knocking down the wall altogether?

If I don't build over the sewer I will lose up to 0.6m from a 3m extension, which is a lot of space!

Any advice would be appreciated.

Thank you,

Nick

 

[freddiemercurystwin]

Single storey? Under PD? Detached or attached? Have you considered building it deeper is where I'm going?

 

[noseall]

As per Freddie - build a bigger extension so as to make lintelling over the pipe simpler.

Re-new the pipe in plastic where it sits under the extension.

 

[nickldn]

It's a single storey extension attached to the back of a terraced house. It's approved under PD.

Could build 3.5m-4m and apply for retrospective planning permission, but that would take up most of the garden.

The sewer pipe was most probably put down in the 1960's so it's going to need maintenance at some point. Renewing it will add to costs and assume would require Thames Water approval. Relocating it further into the garden has been suggested too, but both are going to be expensive and time consuming options. I don't have the time, or money available to do this additional work right now.

I'm worried about the risk of the sewer going wrong maybe 5-10 years after the extension has been built. What would happen if it needed repair/renewal then?

 

[noseall]

I'm worried about the risk of the sewer going wrong maybe 5-10 years after the extension has been built. What would happen if it needed repair/renewal then?

That's why I suggested you renew it now. It's what we always do with old pipes beneath extensions.

 

[freddiemercurystwin]

What's the pipe made of and presumably you've had a CCTV which revealed conditions to be OK or Thames would have expected replacement now. Pads and beams isn't exactly cheap. You can build deeper under PD subject to approval.

 

[Ian H]

At that age it could be pitch fibre.

You could renew it and if there is enough scope for fall you could even move it outwards.

 

[^woody^]

The sewer wont need repairing unless its damaged now or you damage it during the work.

At some distant future time when you are in the ground just like the sewer and it needs repairing, the company will deal with it one way or the other. There are thousands of extensions built over sewers.

 

[Nige F]

Even collapsed pitchfibre can be re rounded and lined

 

[Ian H]

I suppose so Nige

They say it has asbestos in it now.

 

[noseall]

The sewer wont need repairing unless its damaged now or you damage it during the work.

Highly likely if it is old salt glaze with tarred rope and mortar joints. That stuff hates anyone going anywhere near it. Disturb the stuff at your peril. Even the Supersleve stuff is rushed/cobbled together on sites. Always seems as though it is under stress.
If it is encased in concrete and you need to chop any of the concrete away - good luck.

 

[^woody^]

Highly likely if it is old salt glaze with tarred rope and mortar joints. That stuff hates anyone going anywhere near it. Disturb the stuff at your peril. Even the Supersleve stuff is rushed/cobbled together on sites. Always seems as though it is under stress.
If it is encased in concrete and you need to chop any of the concrete away - good luck.

I've got the opposite view. Don't trouble the drain and it won't trouble you.

 

[noseall]

I've got the opposite view. Don't trouble the drain and it won't trouble you.

"...and away goes trouble down the drain....Last night a DJ saved my life......."

Trouble is, you are working near it and you only need to sneeze near salt glaze and there can be trouble. We like to have a nice shiny, straight as an arrow drain ready for the inevitable post extension drains survey. Those old salt glaze fellas are not very photogenic.

 

[chappers]

don't worry about it complete the works as per your BO agreement,. It is then in the hands of the water authority they will deal with it as and when the need arises, they will reroute it if necessary when the time comes.
Just work with caution so as not to disturb it.