An accessory dwelling unit (ADU), also known as an accessory apartment, second unit, or granny flat, is a type of living space located on a single family lot that is distinct from the main residential unit. ADUs are equipped with fully functional kitchens, a bathroom, living and sleeping spaces. There are three types of ADUs:
- Interior—ADUs are housed within the main dwelling and typically consist of a converted basement or attic.
- Attached—ADUs are built as additions to the main structure.
- Detached—ADUs are stand-alone structures.
Benefits of ADUs
Property owners may benefit from extra income generated by renting out an ADU. Homeowners and ADU occupants alike can benefit from companionship, assistance, and the security of living in close proximity. Furthermore, homeowners and ADU occupants may choose to create arrangements in which childcare, light maintenance, or other services are provided in exchange for reduced rent. These potential benefits are especially significant for older adults, as they can support aging in community.
Community benefits of ADUs include land conservation and an increase in (affordable) housing supply. Importantly, ADUs can be built to blend in with the aesthetic of a community. The cost of constructing an ADU can be lower than new construction because the land is already developed and the unit can be hooked up to existing utilities.
Regulatory Barriers to ADUs
Unfortunately, local zoning ordinances and growth limitations may prevent ADU construction. Places that have successfully promoted ADU construction, some even in the face of growth restrictions, include:
- An ADU Zoning matrix lists several west-coast cities have permissive codes that eliminate common barriers to ADUs
- Portland, Oreg., which has been noted for “strong land use control and growth management policies,” relaxed its ADU regulations in 1998 with “no significant negative issues.”
- The town of Wellfleet, Mass., has responded to an increased need for housing (especially among seniors), by approving 16 ADUs since 2006. The success of these units can be attributed in part to a loan program for developing affordable ADUs, and is all the more commendable in light of the fact that 70% of the land in the town is protected from development.
Delaware State Housing Authority (DHSA) Recommendations for ADU Regulations
The Delaware State Housing Authority has developed an excellent, online publication that highlights the ADUs as a practical option to promote housing affordability. It provides the following recommendations to local government policymakers that may be considering developing ADUs regulations:
- Conduct a housing needs assessment to determine the current need and demand for rental units in general, and ADUs
- Ensure that ADU conversions do not result in too many units that will surpass the community’s need
- Determine a good definition zoning code definition of the term ADUs
- Determine where ADUs will be permitted and the minimum lots’ size
- Decide whether ADUs can be regulated by either as a permitted use, with an administrative review, or as a conditional use, subject to public hearing
- Develop guidelines that govern the design and appearance of homes with ADUs to preserve the visual and single-family character of a neighborhood
- Determine if zoning code regulations and standards will allow ADUs to be attached, detached, or both
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