Hi everyone, I wonder if anybody can advise on this. We have a public sewer 600mm D across our garden, with 2 manholes either side of our house. We want to extend the house 3.5m into the garden and that means the extension will go over the pipe.

We have already come 1m away from the manhole but now the architect is saying that in that case our foundations need to be 3m deep (the depth of the sewer) Otherwise we will need to come 1.5 m away from the manhole to have less deep foundations. We are on clay soil so they need to be deep anyway but not as much 3m.

I have contacted Thames Water for some advice but I wonder if anybody has any advice or any way around? If we have to be 1.5m from both manholes, is there a different system we could use to built our external walls that are thiner and can take less space? Thank you in advance