Building over inspection chamber

[ban-all-sheds]

Contemplating a rear extension, which I knew would involve building over a sewer, but I wasn't overly concerned about that because I knew that could be done.

I was pretty sure that it would not entail building over an inspection chamber.

Having looked on the ground to see where the walls would actually be, I found it would be a close thing - they would almost, but not quite, go over the manhole cover.

But then I thought - uh-oh, what about the fact that the footings will be wider than the wall. And I wondered how large the inspection chamber actually was, so I lifted the cover to take a look.

To my dismay, I found that it was larger than the cover - it extends about 30cm on one side:




This is where the walls and footings would be:



Is this remotely do-able? Or are my only options going to be to change the design so that the walls are further away (i.e. make the extension smaller ) or to "move" the inspection chamber?

 

[jeds]

Is the drain public or private? If it's private you can more or less do what you like. But if it's public the Sewer authorities won't allow a cover inside a building.

 

[ban-all-sheds]

Is the drain public or private?

It's public - was recently adopted. Serves 2 or 3 households.

If it's private you can more or less do what you like.

I'm more concerned right now with the "what can be done" than the "what may be done".

But if it's public the Sewer authorities won't allow a cover inside a building.

There won't be - the actual cover will remain outside the building.

 

[mfarrow]

Why are your footings so wide on the photo? Surely it's only extending 15cm from the wall, looks like 30cm to me.

It won't be beyond the wit of man to lintel over the top with water authorities permission (albeit unusual) but with all the pipes coming in, it may be more worth your while relocating the chamber a little way upstream and re-jigging the pipework. You'll be exposing a large amount of it when you dig anyway.

 

[ban-all-sheds]

Why are your footings so wide on the photo? Surely it's only extending 15cm from the wall, looks like 30cm to me.

Doh!

Can't believe I did that. What a t**t.

It won't be beyond the wit of man to lintel over the top with water authorities permission (albeit unusual)

I thought it might be, but as little more than an educated guess. I'll try to run it by them and see what they say.

but with all the pipes coming in, it may be more worth your while relocating the chamber a little way upstream and re-jigging the pipework. You'll be exposing a large amount of it when you dig anyway.

Don't know what routes the underground pipes take, or how easy it would be to do that.

It sits in the shared driveway between me (the RH of a pair of semis) and the LH of the neighbouring pair.



What's upstream to the right I don't know.

As far as I can tell (not done any tests), from L-R what feeds into it are:

My bath & kitchen waste

My WC

Neighbour's WC

Neighbours bath & kitchen waste


I think the plastic pipe entering at the top on the RHS is from a WC in my neighbour's extension.

Moving the chamber would mean rerouting 5 pipes from 2 properties....

 

[maltaron]

You will need to approach your local Water Authority for a build over agreement which they may or may not grant. This applies if a sewer is within 3 metres of the proposed building.

 

[Hugh Jaleak]

I'll hazard a guess Building Control will want that plastic connection altering to a proper backdrop (rather than current affair) if you start altering (or moving) that chamber..... TBH it may prove difficult to try and do too much to the existing chamber, (top half looks to be in poor condition), so you may need to budget for shifting the lot slightly to one side to miss the extension footing.....

Water Co. may also insist on a CCTV survey of the drain where it runs under proposed build, if they aren't happy with it then they may require either replacement or lining. Sometimes with salt glazed drainage (even from as recent as the 1940's) it's only the surrounding soil holding it together, and if roots have made an entrance......

 

[ban-all-sheds]

You will need to approach your local Water Authority for a build over agreement which they may or may not grant. This applies if a sewer is within 3 metres of the proposed building.

I know.

 

[ban-all-sheds]

I'll hazard a guess Building Control will want that plastic connection altering to a proper backdrop (rather than current affair) if you start altering (or moving) that chamber.....

Which would be b****y annoying, as my neighbour (who is a builder) installed that when he built his extension 7-8 years ago, so presumably it was approved then.

I was wrong, above BTW - the connection into the top of the chamber is from the kitchen in my neighbour's extension, and the one which I said was his bath & kitchen is his bath & utility room (was kitchen). His new WC connected to his existing SVP above ground.

This drawing shows in red, more or less, where the main channel runs, and what connects to it at the chamber. (No idea if the pipes follow those straight-line paths.)

TBH it may prove difficult to try and do too much to the existing chamber, (top half looks to be in poor condition), so you may need to budget for shifting the lot slightly to one side to miss the extension footing.....

I have a nasty suspicion that moving the chamber is likely to be too expensive. Might just have to make the extension narrower

Were it not for the fact that the chamber extends beyond the opening, that wouldn't have been too bad, but as it is I'll have to come in by 30-40cm.

Water Co. may also insist on a CCTV survey of the drain where it runs under proposed build, if they aren't happy with it then they may require either replacement or lining. Sometimes with salt glazed drainage (even from as recent as the 1940's) it's only the surrounding soil holding it together, and if roots have made an entrance......

This is 1950's vintage. But all that's got to happen anyway - even if there had been no chamber there, or if I never planned to get close to it, I'd need a build-over agreement. Can't worry about CCTV costs or whether the sewer is in a state - que sera sera.

My immediate concern is whether I would in any circumstances be able to have the side wall where I want....

 

[masona]

My immediate concern is whether I would in any circumstances be able to have the side wall where I want....

See what they say first, if you do make the side wall narrower, could you not extend the back wall inline with next door to make up for it?

 

[ban-all-sheds]

See what they say first,

Indeed - I've sent photos and my drawing to Thames Water to see what they say. I'm sure that there would be a solution from an engineering perspective, but there's no point me stumping up for a SE and a build-over application if they are going to reject it out of hand.

if you do make the side wall narrower, could you not extend the back wall inline with next door to make up for it?

Possibly. It would take it out beyond the 45° line to my LH neighbour, but it's an L shaped extension any way, so it wouldn't make it overbearing.

But I'm not sure if that would buy me anything useful....

 

[noseall]

We once built an extension that actually 'absorbed' one of the inspection chamber walls into the sub-dpc wall of the extension.

It involved excavating up to the chamber each side, concreting the founds so that they butted up to (slighty below) the chamber bottom, then building the masonry up to ground level.

The chamber masonry was re-hashed from ground level up and all was built in tandem with the extension using concrete lintels for bridging and leaving what was a neat finish to the I.C.

All you see now is a chamber lid more or less butted up to the extension wall two courses below dpc. Lift the lid and you will see a (slight) corbel arrangement using concrete lintels etc.

As said, once you start excavating things become clearer to see and easier to rectify. It always seems more difficult whilst stuff is buried beneath the ground, but once the the 'rats' start exposing stuff then solutions become a lot less difficult.

 

[mfarrow]

As said, once you start excavating things become clearer to see

Agreed, get it exposed. You don't want anyone (water co, structural engineer, builder) making assumptions as to what things look like underground, unless you wish to become part of the statistic of homeowners who pay for things twice when extending.

 

[masona]

if you do make the side wall narrower, could you not extend the back wall inline with next door to make up for it?

Possibly. It would take it out beyond the 45° line to my LH neighbour, but it's an L shaped extension any way, so it wouldn't make it overbearing.

But I'm not sure if that would buy me anything useful....

Unknown to me my architect told me the 45° line is from the centre of the window, I thought it was from the jamb side of the window or door.

If you look at my plan, the kitchen is a single storey which you can go further out as it's a lower level building so this wouldn't effect the 45° line but a 2 storey building is a difference matter

 

[masona]

We once built an extension that actually 'absorbed' one of the inspection chamber walls into the sub-dpc wall of the extension.

Wouldn't have a photo for us to see?