A specific type of conversion of existing space that is contained entirely within an existing or proposed single-family residence. 4 ADUs tend to be significantly less expensive to build than new detached single-family homes and offer benefits that address common development barriers, such as environmental quality. Because ADUs must be built on lots with existing or proposed housing, they do not require paying for new land or other costly infrastructure often required to build a new single-family home. Because they are contained inside existing or proposed single-family homes, JADUs require relatively modest renovations and are much more affordable to complete.

ADUs are often built with cost-effective one- or two-story wood frames, which are also less expensive than other construction types. Additionally, prefabricated ADUs (e.g., manufactured housing and factory-built housing) can be directly purchased and can further reduce construction time and cost.

ADUs can provide as much living space as apartments and condominiums and work well for couples, small families, friends, young people, and seniors. Much of California’s housing crisis comes from job-rich, high-opportunity areas where the total housing stock is insufficient to meet demand and exclusionary practices have limited housing choice and inclusion. Professionals and students often prefer living closer to jobs and amenities rather than spending hours commuting.

Parents often want better access to schools and do not necessarily require single-family homes to meet their housing needs. There is a shortage of affordable units, and the units that are available can be out of reach for many people. Homeowners can construct an ADU on their lot or convert an underutilized part of their home into a JADU. This flexibility benefits both renters and homeowners, who can receive extra monthly rental income while also contributing to meeting state housing production goals. ADUs also give homeowners the flexibility to share independent living areas with family members and others, allowing seniors to age in place, even if they require more care, thus helping extended families stay together while maintaining privacy.

ADUs provide housing for family members, students, the elderly, in-home health care providers, individuals with disabilities, and others at below market prices within existing neighborhoods. New policies are making ADUs even more affordable to build, in part by limiting the development impact fees that local jurisdictions may charge for ADU construction and relaxing local zoning requirements. ADUs and JADUs can often be built at a fraction of the price of a new single-family home, and homeowners may use their existing lot to create additional housing. Often the rent generated from the ADU can pay for the entire project in a matter of years. ADUs and JADUs are a flexible form of housing that can help Californians more easily access job-rich, high-opportunity areas. By design, ADUs are more affordable to renters and can provide additional income to homeowners. Local governments can encourage the development of ADUs and improve access to jobs, education, and services for many Californians