Downstairs WC soil pipe through floor slab

28 Dec 2021
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United Kingdom
Hi all,

We’d like a toilet downstairs, but there are some isues. Our drains are at the back and feed into the main sewer at the back of our garden, so the existing soil stack (and the new pipe) MUST be at the back (WC goes under the stairs).

Unfortunately, our foundation is solid concrete all over, so slab. Am I correct in assuming that digging the foundation will affect the structural integrity of the house?

In a way, the load resta on the margina of the foundation, around the house, so digging a channel in the middle shouldn’t have too much of an impact, but because it’s quite long and fairly close to the edge, I can’t imagine the house not moving.

Any thoughts and potential solutions?

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Unfortunately not. It’s a terraced house, so a lateral wall is not an option. The only possible space is under the stairs, so the toilet would face the front of the house and the back of it/soil pipe would be directed towards the back of the house, where the sewer is.

The builder seems very confident he can pay the pipe through the slab, despite it not being easy, I just can’t think that won’t compromise the integrity of the entire foundation.

We’re literally talking splitting open a homogenous whole that hols the house up.

Are my concerns founded or is that not the way it works?
Are you saying it's a concrete floor slab or a raft foundation? Anyway, can't you run the soil pipe along the party wall and box it in? Or consider a dreaded macerator.
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If it's an extra toilet mainly for no 1's a macerator is def an option. I know peeps don't like them (as @cdbe above), but I had to fit one in our under-stairs because even though against an outside wall, our sewer is so shallow at the side of the house we couldn't keep the pipe underground and get a fall. Took the 32mm discharge from the macerator horizontally through the insulation behind the plasterboard in the next room to the stack. We have a sanitop Up that takes the sink waste as well. Quiet, unobtrusive, works, and solved the drain problem.

It was around £350. Been working away happily for 3 years now. Be quite honest, once it gets to 5 years plus and if it has a problem, I'd prob just unclip it and drop a brand new unit in.

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