Help please! Drains, pumps and a basement!

[siftingflour]

I would really like your advice/experience

builders started work a month ago on a 3m full width extension. It is in the basement of an old victorian house.

The architect has just contacted me and said there is a problem: the main drainage pipe for my neighbours houses runs through my garden but we cannot build the extension over it, as Planneded.

The architect says he had seen this drain on the drain plan but had not physically lifted the decking in the garden to look at it. When the builders removed the decking they found that the pipe was so shallow there isn’t even a manhole. The flow of the water in the drain run means it cannot be buried any deeper.

The architect says the only solution is for every single bit of water - rain in the gutters, loo flush, kitchen sink and washing machine - the whole caboodle - to go through drain pipes built under the new extension and then into a very deep purpose built cavity in the garden - where everything will be electrically pumped up and into the main drain (which will also be relocated).

This will cost an additional 30,000 (around a tenth of the total project cost and not budgeted).

The big issue of cost aside, I am reluctant: this will make my house entirely dependent on an electric pump not to flood with rainwater or back up with sewage. If there are power outages, heavy storms, I could have problems. I will have to get a back up battery, pay for an annual service plus put an electricity board in the garden. I am going to rent out this house in the short term and so I will also need to rely on the alertness of tenants to report faults. I am thinking of cancelling the extension.

The architects say there is no other solution. I have signed a contract with the builder.

My questions are:

1. if you have experience with pumps and sumps. Are they reliable? Particularly for a project of this size? Do you think my qualms about being reliant on a pump to protect my house are valid? What would you do (money aside)?
   

And:

Should the architect have visually id’d the drain (removed the decking to do so) or is this just one of those unexpected errors that come up on site.

Thanks!

[polyjuice]

I wouldn’t do this. I know someone who had exactly the same issue discovered at a much earlier stage and the architect advised them not to touch it. Pumps fail and go wrong and the price you are being quoted sounds very low for the extensive solution that’s required. I would also query if consents might be required from others whose drainage is affected. The risk for you if it goes wrong and backs up is also there. What a pain for you - you have been really badly advised. hope you manage to resolve it.

[Archipops]

the site investigation is quite fundamental, especially something that could decide the feasibility of a project, and that would include checking the sewerage pipe levels. This is normally done at the initial stages much prior to construction. it’s not your fault