(1) Except otherwise provided in section 14 or as shown in the plans approved by the local authority, the surfaces of contact between a foundation and any wall, pier or column, and all bottom surfaces of foundations, shall be horizontal or in the form of steps with horizontal and vertical surfaces.

(2) Where such steps are made in the longitudinal section of the foundation, the portions of the foundation on adjacent levels shall overlap for a distance at least equal to the vertical thickness of the foundation or the difference between adjacent levels, whichever is greater.