Unused spaces in basements, attics, and garages are widely available for smaller units, as are large apartments that can be subdivided. The potential new supply of smaller units, then, is very large and could increase population density far more than might be desired in most neighborhoods. Changing zoning rules, then, involves two important questions: (1) How many new smaller units are needed to release larger units sufficiently to bring rents down broadly? And (2) How much increased density will be acceptable to a city or town’s residents? The first question can be answered by economists. The second question is a community decision. Keep in mind that controlling the number of available housing units is an important way to control population as well as rents. More units mean somewhat more people and lower rents.