Foundations - drain in the way

[Graeme2019]

Hello all,

I am looking for some advice, building a garden shed.
There is a drain in the way of where I would like to build the foundations, it only serves my property and is 1 pipe in and 1 out. Northumbrian water have said it's private and they have no issues with me moving it.

The drain is about 0.6m deep, there is a Buchan trap inside the drain and it slopes down to the back sewer to about 1.2m. I have dug the foundations down to be 0.8m which should be below the invert of the drain pipe. So shouldn't be any load imposed on the pipe.

My question is, am I ok to smash out the bricks of the chamber and use shuttering or move the chamber

wall to the edge of the foundation and rebuild before the concrete is poured?

I'm probably over thinking it, but the last thing I want is to wreck the drainage line and have my new shed and existing wall have to be torn down to repair it.

Any advice appreciated.

 

[tony1851]

It looks a mighty deep foundation for a garden shed?
Anyway, why not leave the chamber undisturbed and put a concrete lintel astride the wall of the chamber, supported off the
foundation wall each side of the chamber.

 

[Graeme2019]

Hi Tony,
Thanks for your reply. Will it be OK to leave a gap in the foundation between the chamber? This sounds like a better option as I don't really want to damage the chamber or pipes.

The foundations is about 0.8m to be below the drain pipe. It's not a timber shed, will be blocks / brick single skin.

 

[tony1851]

Yes, you'd just leave a gap in the concrete foundation and wall where the chamber is, so that there is no physical contact with the new work.
The concrete lintel just forms a bridge over the chamber wall, parallel to it, as long as there is sufficient space left to take up the lid.

 

[^woody^]

Being as the manhole did not suddenly appear, why didn't you just plan to build the shed so that it comes short of the lid edge, and bridge the manhole with a lintel?

 

[Graeme2019]

I pulled a string line along the side of the house, so that the shed walls would align with the house. I guess I could have moved it back away from the edge a bit, but then thought it would be too narrow inside the shed.

A lintel will go over the lid and allow it to open; I wasn't sure that you could have a break in the foundations.

I had hoped to move the chamber back over (towards house) to make a new toilet connection and put a straight through pipe in the existing chamber and remove it... But then realised it had the Buchan trap in there and couldn't move it.

 

[^woody^]

A lintel will go over the lid and allow it to open

No that's crap. The lintel should bridge the brickwork only, so that the lid is just outside the face of the shed wall.

 

[Graeme2019]

Yeah Woody that's what I meant. It will go over the brick work only, not the actual lid of the chamber.

I'm guessing as both you and Tony have mentioned it, the lintel option and split foundation is best. I will go with that. Cheers

 

[Hugh Jaleak]

No reason you cannot remove the Buchan trap. They are an antiquated idea, and serve no real purpose nowadays.

 

[Graeme2019]

Thanks Hugh. My original idea was to take out manhole and trap, put a straight through in after foundations are poured and move the chamber a couple meters closer to the house for a new toilet connection. That's why I dug the foundations right upto manhole. I wasn't 100% sure this was alright, so thought I'd check on here.

I thought the purpose of the trap was to keep out sewer gas and also something to do with keep water flowing due to the fall after the trap?

 

[John D v2.0]

I thought the purpose of the trap was to keep out sewer gas

yes basically they used to think disease was caused by bad smells, and the drains are full of bad smells. By that time, they knew about microbes, but people's trust in science in those days was similar to now, so they still fitted them long after they knew it was unnecessary!

 

[^woody^]

If there is no reason to waste time and expense doing something, then don't. The trap and manhole can stay.

 

[noseall]

Hoof that god awful antiquated junk out and re-build a free flowing placcy fella, that is likely to end up out of the danger zone. You won't regret it.

 

[Ian H]

I’d get rid of it too. The trap won’t go much past the outside wall of the manhole anyway.

It might be 6” though so have a reducer and 6” clay to plastic ready..

 

[Hugh Jaleak]

Basically the only purpose of the trap was to seal the house drains off from the main sewer. The Victorians believed 'Drain air' was the root of all their health issues, so set about devising methods of keeping it away from the house. The Interceptor or Buchan Trap was their answer, a rodding eye was provided to give access beyond it if need be, this was sealed with a removeable plug.

A low level AAV was fitted nearby and connected to the chamber with the interceptor, the idea being, air passing over the top of the soil stack would draw air in through the low level vent, and out the stack, thus ventilating the house drainage system and ward off disease.

The only thing you need to keep from that lot in a modern system is the open vent on the stack at the head of the drain.