Building an extension over a drain?

minibbb

Evening all

We're hoping to extend our 1930s semi by adding a kitchen/diner to the rear. The trouble is this involves building over a sewage inspection manhole. Having looked down it, it has a branch for our soil pipe (which will be moved if we extend) and appears to also take the neighbour's waste. She flushed her toilet for us though and nothing appeared! There was tissue etc on that side though so clearly belongs to a house somewhere!

We have to apply for a build over agreement with southern water for £950 which includes a CCTV survey. They've told me if the drain serves a neighbour we'll probably have to move the sewage run.

Has anyone had to do this on their own extension? Ours will be 6m by 2.5m so not huge but will make our house a heck of a lot more liveable!

bridgedino

We did exactly the same. Scottish water insisted on a cctv survey. We ensured that the build included replacing the old shared clay pipe with a new clay pipe.

All done and no concerns about any old clay pipes collapsing

minibbb

That's really handy thanks! Did you have to move the manhole outside the build or just cover it over altogether?

Davesnave

minibbb wrote: »

That's really handy thanks! Did you have to move the manhole outside the build or just cover it over altogether?

It will have to be moved. There isn't any good reason to have one inside a building and they aren't there for decoration.

In the context of adding a substantial extension and moving/replacing a pipe run to do so, a new inspection chamber is just one detail.

There will be stipulations about foundations if you build over or alongside, which may have cost implications, but obviously those will depend on the specifics of the site.

Gloomendoom

Davesnave wrote: »

It will have to be moved. There isn't any good reason to have one inside a building and they aren't there for decoration.

We have one inside our house and it hasn't been any problem. It was hidden under carpet tiles when I bought it.

Having said that, after the experience my sister had with a shared manhole outside the back of her old house repeatedly blocking up and blowing the lid off, I wouldn't have one inside out of preference.

Davesnave

Gloomendoom wrote: »

We have one inside our house and it hasn't been any problem. It was hidden under carpet tiles when I bought it..

Yes, but would the BCO pass it nowadays?

We are not talking 20th century....

Gloomendoom

Davesnave wrote: »

Yes, but would the BCO pass it nowadays?

We are not talking 20th century....

I'm not sure that my drain is even 20th century.

However, it is double sealed and screwed down so, yes, it does meet current building regs.

Davesnave

Gloomendoom wrote: »

I'm not sure that my drain is even 20th century.

However, it is double sealed and screwed down so, yes, it does meet current building regs.

We had those in the place where I worked. Built 1953.

It wasn't very nice in there when Mr Dyno-rod had to call.....

Heedtheadvice

As regards foundation mentioned above: did an extension recently that was close to drain. Had to dig down far enough so that the foundations were at least below a line drawn at an upwards angle of 45 degrees from the bottom of the drain at it's lowest point. That is to prevent pressure from the building on the drain.
I actually went down a bit further than that.

Your local building control officer will be able to advise as they will have to approve what is to be done anyway so PPPPPP (proper planning prevents ......etc.)

Gloomendoom

Davesnave wrote: »

We had those in the place where I worked. Built 1953.

It wasn't very nice in there when Mr Dyno-rod had to call.....

By a strange coincidence, I'm pretty sure that this particular drain cover dates from that exact year.

Luckily, Mr Dyno Rod has never had to call. If he does, I will probably take a month's holiday to give the air a chance to clear.

Davesnave

I was unlucky. My sewer was 2 metres down and I had to bridge it at an angle, which involved a huge reinforced lintel, about 5m long, cast on-site + a second, much smaller.

On the positive side I had a friend who was a structural engineer and a relative with a digger.