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Accessory Dwelling Units (ADUs)

While their forms vary, ADUs share some common traits. They’re always secondary housing units on single family residentially zoned lots and are a unique category of housing. ADUs also have some other distinguishing characteristics:

  • ADUs are accessory and adjacent to a primary housing unit.

  • ADUs are significantly smaller than the average US house.

  • ADUs tend to be one of two units owned by one owner on a single family residential lot.

  • ADUs tend to be primarily developed asynchronously from the primary house by homeowner developers.

  • A large range of municipal land use and zoning regulations differentiate ADU types and styles, and dramatically affect their allowed uses

  • Many informal ADUs exist compared to permitted ADUs.

These characteristics make ADUs distinct from normal housing. The Portland area is relatively friendly to the best practices of ADU development.

  • Detached new construction

  • Backyard cottages

  • Granny flats

  • Laneway houses

  • Garage conversion ADUs

  • Carriage houses

  • Addition ADUs or “bump-out ADUs”

  • Basement conversion ADUs

  • Basement apartments

  • Mother-in-law units, in law units, secondary suites

  • English basements

  • Accessory apartments