Am I responsible?

[siftingflour]

I am in a bit of a mess. I signed a contract to build an extension but in doing the works (two weeks in) the builders discovered that the drains were too shallow to build the extension as planned.

I have been told by the architect managing the project that I am liable to pay the builder for all the work I signed for, and that not doing the extension will be hellishly expensive. They are urging me to move forward by making the entire house dependent on an electric pump, which I do not want to do (and I would not have agreed to this project if that were the condition). Meanwhile the house has been gutted and the garden excavated so it's not a question of walking away from building works - I am going to have to reinstate everything as well as pay the builders for any loss of earnings.
My question now is: where does the responsibility lie? Should the architects have established the depth of the drains before works started? They say it was hard to do this as the drains were not easily accessible (part buried under concrete).

I would say that the fault lies with the architect. Surely it is their job to ensure your property is able to utilise the extension they designed, otherwise what are you paying them for? Id query this with your local council or an independent body for architects. I don't see how this is your fault, or the builders!

Have you checked your contract? I'd imagine they will have some small print explaining they are not responsible for this type of problem.

Are there any other ways to move forward with the project?

But if the drains aren't easily accessible how do they expect you to know their depth? Or indeed what depth they need to be? That's what you pay an architect for surely?

I think you need legal advice tbh, but it doesn't sound right that you can be held responsible

Architect should have found this. Their failure

Take legal advice. Check any insurance policies you have for legal expenses insurance. This could turn into a hefty dispute.

Loss of earnings? Fuck that.

Pay them for the work they have done, and the reinstatement. Then they can just move onto their next job in the wait list. No loss of earnings.

I feel so sorry for you OP. Definitely get legal advice. I am sure you aren't liable for the whole cost. Are there options where you can move the drain, or build in a way that doesn't require such deep foundations? (Timber frame??)

Well it's up to the architect to find a solution, which it sounds like they have, but it's not acceptable to you.
So ideally they should find another alternative if it's possible.

Why cannot they use the existing drains by altering the plans? Why are they too shallow (not deep enough I assume). You are presumably using them already so why are they not deep enough now?

This should not be a deal breaker of this magnitude. How deep is the drainage system in the pavement outside the property? Why cannot the existing drains cope?

Alternatively - Get the pump? Is it worth this agro not to have it?