While it’s unknown who coined the term ‘Accessory Dwelling Unit’ also known as ‘ADU,’ there is a long history of this building type in the United States. In an article titled, “ADUs Are an American Tradition,” the historic carriage house or coach house is described as a precedent for the modern day ADU. “Originally built for horse-drawn carriages, the structures…were frequently large enough to double as living quarters for workers…Decades later, in response to housing shortages and economic needs, many surviving carriage houses were converted into rental homes.”
Following World War II, the rise of neighborhood developments that centered around the suburban single-family home coincided with residential zoning codes that typically limited the allowance of only one home per lot, which meant that ADUs could no longer be built legally by homeowners or developers. Over three decades later, to support smaller and more affordable residential options for expanding housing needs, many cities across the United States began to revisit ADUs as a possible building type with a variety of positive benefits. In more recent years, the increasing cost of housing has driven many cities to revise zoning codes to legalize and encourage the creation of ADUs.
Simply put, an ADU is a small residence that shares a single-family lot with a larger, primary dwelling. Based on size, ADUs are typically less expensive to build than larger, standalone homes, but can often increase property value or generate additional income. They can also take into consideration a larger variety of socio- or socio-economic preferences of residential living such as multi-generational or cooperative housing.
