as defined in Government Code Section
65915(i), means a development project for five or more residential units. For the purposes of this chapter, "housing development" also includes a subdivision or common interest development, as defined in Civil Code Section
4100, as approved by the City, and consists of residential units or unimproved residential lots and either a project to substantially rehabilitate and convert an existing commercial building to residential use or the substantial rehabilitation of an existing multifamily dwelling, as defined in Government Code Section
65863.4(d), where the result of the rehabilitation would be a net increase in available residential units. For the purpose of calculating a density bonus, the residential units shall be on contiguous sites that are the subject of one development application, but do not have to be based upon individual subdivision maps or parcels. The density bonus shall be permitted in geographic areas of the housing development other than the areas where the units for the lower income households are located.