One of the most significant trends in recent 'green' design is the appreciation of the role of embodied carbon. Heretofore, the focus had been almost exlusively on reducing carbon produced after a house was built - it's operational footprint. But we are now beginning to realize that the carbon cost of materials and practices of the build can match or exceed those of its (expected) lifetime operation.
The most common modern building materials, such as concrete and steel, are tremendously energy- (hence usually carbon-) intensive to produce, so sustainable design demands we critically assess their use in the reactive house. Concrete alone is a remarkably complex subject - mitigations typically involving reduction/substitution of the Portland cement (the main carbon culprit) with fly ash, pozzolans, Co2 injection, etc. Moreover, most of these techniques are not available as options for residential construction, so the only levers we can directly pull are reduction in the amount of concrete used, or substitution of another building material for concrete.
Foundations are one area where few alternatives to concrete exist - the strength and moisture tolerance are difficult to match. Using a slab foundation, rather than a full basement, can greatly reduce concrete poured, but at a cost of loss of flexibility in utility service provision and repair, cool storage, etc. Partial basement (for services) is another strategy for reducing material and excavation.