I was looking at doing this a while ago (ended up doing standard under-counter due to complications fitting the consumer unit etc in as well) .. I thought the easiest option was to make something on site.. this was my inspiration:
Met with a ground worker last week, nice guy, knew is stuff and spent a good hour on site talking through how to do the ground works.
I need to look into their previous work, as this is a 3 sided basement dig with retaining walls and want to make sure they have done something similar.
One thing that stood out was he wants to do the works on a day rate, and will estimate the time to do the works.
That worries me as it transfers the budget risk all onto me. I would of thought that a ground worker would be give me a fix cost with an uplift for risk for them and out of scope work (e.g hitting granite etc)
They have the ground investigation, an good estimate of how much muck is coming out.
When I raised it with him he said it would cost me less, which it may well do but not sure I want to shoulder all the risk.
I am going to be on site every day (it's a garden plot) and work locally so I can observe what they are doing.
The ground works are a big part of this this project and will be largest package of work in terms of cost, so don't want to get burnt from the outset.
I guess if I get a fixed cost quote from another ground worker it might give me a steer on things.
Answers on a postcard?
My project is incredibly structurally complicated - we have about 12 RSJs and 7 or 8 columns, and we're dealing with a property that is almost 100 years old and has a fairly random pattern of differing corbel heights as its foundations. You'll therefore understand why I'm confused by the suggestion that I (a layman with no engineering expertise) can second guess my structural engineer and tell him that he has to do away with the concrete subfloor. He has specified it for a reason.