All floors at grade or below grade subject to hydrostatic pressure shall be designed to resist a uniformly distributed uplift equal to the full hydrostatic pressure, unless a system of exterior footing drains and under floor drains are installed to prevent the development of such hydrostatic pressure in the event that the soils at the site of the building are highly impervious and the only water seepage anticipated is penetration downward from ground surface rather than upward from below, the exterior footing drain system would be considered adequate without the requirement of an under floor drainage system with the approval of the Director of Building and Zoning. (M.C. 1963, § 22.903(c); Ord. No. 0-64-29; renumbered Ord. 0-77-60, 9-19-77)