Section 27-658. Depth of foundations

(a) Footings and Pile Caps. The bottom
  surface  of  any  footing,  pier,  pile   cap,   or   other   foundation
  construction,  other  than  grade  beams, shall be carried down at least
  four feet below the lowest level of the  adjoining  ground  or  pavement
  surface that is exposed to frost, except as follows:
    (1)  In  refrigerator, cold storage, or similar areas, the depth shall
  be increased as required to found the construction below  the  potential
  level  of  freezing  in the soil, or loss of heat from the soil shall be
  prevented  by  insulation,  warm  air  ducts,  circulating  systems,  or
  equivalent means.
    (2)  For foundation elements resting on rock, the footings may rest on
  the rock  surface  at  shallower  depths  than  those  indicated  above,
  provided  that visual inspection of the rock surface directly underlying
  the bearing area shows it to be free of seams, cracks, or  disintegrated
  materials  that  could serve as reservoirs for water and thus be subject
  to freezing.
    (3) For foundation elements in  the  interior  of  closed  and  heated
  buildings,  or  in cases where the soil underlying the foundation is not
  subject to frost action, there shall be no mandatory minimum requirement
  for embedment.
    (4) Mobile or portable buildings not more than one story high  may  be
  supported  on  foundation  elements  bearing  at  grade,  subject to the
  following conditions:
    a. The building shall be supported on jacks, wedges, or other  devices
  that will permit readjustment of level in the event of displacement.
    b.  The  bearing  capacity of the underlying soil shall be adequate to
  support the building loads without rupture. Where the building is to  be
  supported  on nominally unsatisfactory bearing materials, the provisions
  of sections 27-677 and 27-679 of article four of this  subchapter  shall
  apply except that, where the bearing material is confined under pavement
  and  the  bearing  pressure on the surface of the soil material does not
  exceed five hundred psf, special investigation of  the  foundation  will
  not be required.
    c.  The  bearing  area  shall  be  well  drained  and  not  subject to
  inundation.
    d. The levels of the foundations shall  be  checked  and  adjusted  to
  compensate  for  displacements  at  least once every year, and the owner
  shall maintain a record of such work, available for  inspection  by  the
  commissioner.
    (5)  Where  piles project above grade and displacement of the pile cap
  is prevented by interposing a space between the underside of the cap and
  the ground, the requirement for embedment of the cap below the level  of
  frost penetration shall not apply.
    (b) Grade beams. The bottom surface of any grade beam shall be carried
  down  at  least  eighteen inches below the lowest level of the adjoining
  ground or pavement surface that is exposed to frost.