When a housing project consisting of a group of two or more buildings is to be constructed on a plot of land of at least three acres and the land is not to be subdivided into the customary streets and lots or the existing or contemplated street and lot layout make it impracticable to apply the requirements of this chapter to the individual buildings in the housing project, the Council, upon favorable recommendation of the Planning Commission after a public hearing, shall apply the requirements of this chapter to the housing project in a manner that will be in harmony with the character of the neighborhood, will ensure a density of land use no higher and a standard of open space at least as high as required by this chapter in the district in which the project is located. In no case shall the Council authorize a non-residential use or a building height prohibited in the district.