(a) Protection Against Action.
(1) When subject to frost action, the bottom of footings shall be not less than three (3) feet, six (6) inches below the adjoining ground surface except that footings for one (1) and two (2) family dwelling houses and similarly lightly loaded buildings shall be not less than three (3) feet below the adjoining ground surface, and except that footings for one (1) story framed structures which, in the opinion of the Commissioner will not be adversely affected by frost action, may be at such depths as will provide adequate support and anchorage.
(2) The bottoms of footings and foundations shall be protected against freezing until backfill or other permanent protective cover is in place.
(b) Footings on Sloping Ground. On sloping ground all footings shall be at sufficient depth so that erosion of the surrounding ground surface will not remove required lateral support or permit sliding or slippage.
(c) Footings at Different Levels.
(1) Where footings not supported on piles are adjacent to sloping ground or where the bottoms of such footings of a structure are at different levels or at levels different from those of the footings of an adjoining structure, the difference in footing elevations shall be subject to the following limitations:
A. When the ground surface slopes downward adjacent to the footing the sloping surface shall not encroach upon a prism of bearing material under the footing having sides that make an angle with the horizontal of sixty (60) degrees for rock and thirty (30) degrees for soil, and the horizontal distance from the lower edge of the footing to the sloping surface shall be at least two (2) feet for rock and three (3) feet for soil.
B. In the case of footings in soil the angle of stepping of contiguous footings, or a line drawn between the lower adjacent edges of adjacent separate footings, shall not be steeper than one-half (1/2) the angle of repose of the supporting soil but in no case steeper than one (1) vertical to two (2) horizontal.
(2) Exceptions. The requirements of this subsection may be modified by the Commissioner where adequate permanent provision is made for lateral support of the material supporting the higher footing or where the average stress in the soil due to a higher footing is not more than twenty-five percent (25%) of the resistance of the soil to sliding as determined by soil tests and stress analyses made in an approved manner by a qualified person or laboratory acceptable to the Commissioner.
(d) Level Beds Mandatory. All footings shall be constructed on level beds.