The Los Angeles County Department of Regional Planning notes that R-3 zoning is for a limited use multiple family residence, such as a small apartment building. The lot size required is at least 5,000 square feet, and each unit must have at least 1452 square feet.
The City of New York, Department of City Planning reports that semi-detached homes, detached homes, small apartment buildings and low-rise attached houses are allowed in R-3 zones. To be classified under R-3 zoning, each lot must meet minimum lot width requirements. The city requires one off-street parking space for every unit built on the property.