The purpose of this section is to provide a method of developing single-family detached dwellings which will preserve desirable open spaces, conservation areas, floodplains, school sites, recreation and park areas and lands for other public purposes by permitting the reduction of lot sizes (and certain other regulations hereinafter stated) without increasing the number of lots in the total area to be developed. Cluster single-family residential developments are permitted in R1 and R2 Districts.