No nonresidential structure shall hereafter be constructed or substantially improved (see Uniform Building Code Section 104(b)) unless the lowest floor including basement is elevated above the base flood elevation or, together with its attendant utility and sanitary facilities, the structure is so constructed that below the base flood elevation the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capacity of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy.  The director of building inspection may require certification of such adequacy by a registered architect or engineer.  (Adding (freeboard) to the elevation of the floodproofing will reduce insurance rates.)  (Ord. S-36983, 1978).