This stage of any building project is where it is hardest to be 'ecological'. Concrete is not an ecological material - too much energy goes into the production of cement and in the transport of stone and heavy materials. But buildings have to have foundations and there are long term energy advantages of sinking the building into the ground rather than lifting it off on stilts. Perhaps when energy costs have risen enormously, it will not be economic any longer to build like this. But at present the costs of a basement built into the ground are low compared with the alternative.