2 Portland Projects Highlight Flexibility of ADUs
As the housing affordability crisis continues, a greater mix of housing types, not just more housing, is needed to meet differing income and generational needs. But the housing types that contribute to a greater mix often involve densities that are higher than what local zoning rules allow. Different ordinances and codes can help increase supply with "missing middle" housing while meeting various market demands.
One example is accessory dwelling unit (ADU) ordinances. These are aimed at generating a dwelling unit that is secondary to the main house on the lot. ADU ordinances are used when there is a need for more diverse affordable housing opportunities within a lower intensity, primarily single-family detached, context. The standards can be in addition to the base zoning or as an independent set of standards.
Typically, an ADU ordinance allows either the conversion of existing structures, such as garages, into secondary dwelling units or new accessory structures to be built within a parcel by utilizing existing available space, usually in the backyard. There are three types of ADUs:
- Detached ADU: A structure completely separate from the primary building, including detached garage conversions or additions.
- Attached ADU: An addition to the primary building outside of the original building’s footprint.
- Internal ADU: Conversion of a part of the primary building to an ADU (e.g., over an attached garage, in an attic, or in a small portion of the primary building's ground floor).