Section 27-686. Foundation walls

(a) Concrete. Concrete foundation walls
  shall be  designed  in  accordance  with  the  provisions  of  reference
  standard  RS 10-3 relating to bearing or retaining walls. The equivalent
  unbraced height of a wall supported by  lateral  soil  pressure  may  be
  determined  by  a  recognized method of elastic analysis. Alternatively,
  such a wall may be assumed  to  be  laterally  braced  at  intervals  as
  follows:
    (1)  Where  fill  is  placed against both faces of the walls: the full
  height of the wall or eight times the thickness, whichever is the lesser
  value.
    (2) Where both faces of the wall are not in  contact  with  soil:  the
  height  of the unbraced section of the wall or eight times the thickness
  of the wall, whichever is greater, but not more than the full height  of
  the wall.
    (b)  Masonry. Masonry foundation walls shall conform to the provisions
  of reference standards RS 10-1 and RS 10-2, and the following:
    (1) TYPES. Masonry foundation walls may  be  of  plain  or  reinforced
  masonry  and  shall  be  of solid units, except that load bearing hollow
  units will be permitted for support of one- and two-story buildings.
    (2) WALL THICKNESS. Foundation walls of masonry shall be designed  and
  constructed  in accordance with the provisions of reference standards RS
  10-1 and RS 10-2, supplemented by the provisions of subdivision  (a)  of
  this  section,  relating  to  unbraced height. The thickness shall be at
  least six inches.