Among the various foundation types, rafts are one of the most well known. They are used above all in ground conditions with little bearing capacity, or with poor quality soil, large thicknesses must be used which increases the construction cost. Thanks to the use of U-Boot Beton® lightened rafts can be created with the same performance but at a considerably lower cost. Once drown in the concrete casting, U-Boot Beton® forms the structure just like two full slabs, with a variable thickness, connected by a perpendicular beam gridwork to form a bidirectional static honeycomb plate. For this concrete bed, the distribution of weights due to hight inertia is rationalised in order to permit maximum stiffness and lightness for the structure with a minimum amount of concrete, which makes it possible to eliminate, where possible, the foundation piles.