Rarely is happen the natural surface of ground to be  perfectly leveled. It is extent and may be an appreciable slope either across or along or both across and along the site of most buildings. On the sloping sites that are a lot, the first decision to be made is whether the ground floor to be above ground (which means at the highest point) or partly sunk below ground. And the stepped strips are build in order to overlap by twice the height of the step. By the thickness of the foundations or whichever is greater, as showed in the images in the gallery.

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