AMENDMENTS TO THE BOCA NATIONAL BUILDING CODE/1996

CHAPTER 18 - FOUNDATIONS AND RETAINING WALLS

(Amd) 1806.1 Frost protection: Except where erected upon solid rock or otherwise protected from frost, foundation walls, piers and other permanent supports of all buildings and structures larger than 100 square feet in area or 10 feet in height shall extend to the frost line of the locality, and spread footings of adequate size shall be provided where necessary to distribute properly the load within the allowable loadbearing value of the soil. Alternatively, such structures shall be supported on piles where solid earth or rock is not available. Footings shall not bear on frozen soils unless such frozen condition is of a permanent nature. 

Exception: Use Group U structures of wood frame, steel or plastic construction, 200 square feet or less in area are permitted to be installed above grade on a base of naturally durable wood, preservative treated wood, concrete, masonry or other approved material. Such structures are not required to be designed to resist or protect against frost action, but shall be designed to resist or protect against movement from wind.