(a) The average density permitted in each residential planned unit development shall be established by the city council, upon recommendation of the planning and zoning board. The criteria for establishing an average density includes existing zoning, adequacy of existing and proposed public facilities and services, site characteristics and the recommended density of any land use involving the area in question. In no case shall maximum density permitted exceed 15 dwelling units per acre, and in no case shall the overall number of dwelling units permitted in the residential planned unit development be inordinately allocated to any particular portion of the total site area.

(b) If a developer elects to develop the property in stages, the cumulative density with each subsequent stage must be approximately the same as the overall density approved for the entire project, in that such cumulative density shall not vary upward more than two units per acre and that upon completion of all stages the final density shall be equal to the density approved in the preliminary development plan.