In multifamily districts, including R-2A, R-3 and RSP-1 Districts, under the same standards of density and development permitted by this chapter, the Planning Board, after obtaining a resolution of authorization from the Town Board, may approve cohesive development of individual or multiple sites to allow row houses (townhouses, patio houses, etc.) of not more than three stories and to allow apartments for either rental, sale, cooperative or condominium use, to a height of not more than six stories. These standards may be applied, provided that the open land resulting from such provision is reserved in open space, and, further, provided that the total plan of development (including the architectural treatment of the buildings, building locations, parking layout, provisions for developed usable open space, parking egress and ingress and appurtenant facilities proposed) is constructed in accordance with a site development plan approved by the Planning Board.