Installing new upstairs toilet, waste pipe underground?

4 Nov 2010
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United Kingdom
Hiya, im in the middle of renovating my house, we are putting a new toilet into an existing upstairs dorma complete with shower and wash hand basin. The architect has on the drawings that the waste will come out the back of the house (oh we are getting a small extension put out our back also) and the waste pipe will run under the new extension, so underground and then into the main drain located in our drive. The builders started the extension and have now got the plumber out, the builders are now saying the the main main drain is not deep enough for us to have it running under the extension, i.e. there is not enough gradient from where it would start underground to where the main drain is and not enough slop so there could be problems in future with blockages etc. The ther alternative was to have the waste pipe running down our downstairs back bedroom, obviously boxed in, and then pipe running under bedroom/hall and into downstairs toilet. Im not entirely happy about the pipe being run inside the house, i know it happens but i would prefer coming outside, can anyone give advice on whether we can make drain deeper or any other way we could do this??
Thanks for reading and hope you can help?? Cheers Angie
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One certainty is water doesn't run up hill.

Has your architect or builder painted himself into a corner with the work they have done already, and is now trying to find another way out?

How much fall do you have, and over what distance for the proposed drain?

Will the proposed drain be above, below or through the new foundations and floor?

IIRC a fall of as little as 1 in 200 is permissible in some circumstances, and incorporating accessible rodding eyes in the run isn't exactly rocket science.

IMO a 'straight down, straight out' arrangement, with a minimum of bends is less likely to be troublesome than a convoluted route through the house
Thanks for you reply....

I do think you might be right about them backing themselves into a corner on this!! I think they should have done the work before putting all the foundations in etc, oh and byt the way i brought this up on day one and they said it should be fine!!

The proposed drain was to be below and through the new extension...

The builders said the existing drain is 2 metre down? But thats what they are saying??

what does IIRC mean sorry?

i totally agree that it would be simpler to come straight out instead of through the house, i think they are looking for an easy way out but i dont know how to prove this, do you think getting someone else out to give me a second opinion would be worth it, who would i even ask?

ta for this so far :)
If I Remember Correctly......

Architect should have measured the invert (depth) of the drain before designing the drainage..... If the builders are saying the drain is 2m deep then to get a 1:40 fall on the run then you'd have to go 80m before getting to ground level. :confused: How big is the extension?

If the builder has screwed up then its down to him to remedy the issue at his expense. I would check with architect, the work should be carried out in accordance with his drawings.
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Architect has agreed to come out tomorrow so will wait and see what he says... The extension is about 18 square metre...

Yeah architect says they should not be changing the plans, but plumber said sometimes the architect does things on assumptions and they have to change things sometimes??

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