As part of a study researching underdeveloped sites, ACHA looked at buildings that do not fulfill the capacity allowed by their zoning. Many of these are one and two-story buildings whose owners cannot afford the loss of revenue during a lengthy construction period. With prefabrication, onsite construction can be reduced to a third or a quarter of the time. The diagram here illustrates how structural reinforcement and utilities are added to the existing building, after which units are delivered and stacked on top of the existing building.