A type of planning restriction applied to certain residential zones in the United States and Canada that limits development by allowing only single-family detached homes. It prevents townhomes, duplexes, and multifamily housing (apartments) from being built on any plot of land that has this zoning designation. It is a form of exclusionary zoning, created to keep minorities out of white neighborhoods. It both increases the cost of housing units and decreases the supply. Source: Single-family zoning – Wikipedia.