Accessory Dwelling Unit (ADU)
A secondary, smaller residential unit on the same lot as a primary dwelling, such as a backyard cottage or garage apartment.
An Accessory Dwelling Unit (ADU) is a secondary housing unit located on the same parcel as a primary single-family residence. ADUs go by many names — granny flats, in-law suites, backyard cottages, garage apartments, or casitas — but they all share the common characteristic of being smaller, subordinate residential units that share a lot with the main house.
Types of ADUs
- Detached ADU: A standalone structure separate from the main house, often in the backyard
- Attached ADU: Built as an addition to the primary dwelling
- Conversion ADU: Created by converting existing space such as a garage, basement, or attic
- Junior ADU (JADU): A very small unit (typically under 500 sq ft) created within the primary dwelling's existing footprint
See Accessory Dwelling Unit (ADU) Activity Happening Now
ZoneWire detects when accessory dwelling unit (adu) is discussed in council meetings across 26+ metros — and alerts you hours after the vote.
How ADU Regulations Are Changing
ADU policy has become one of the most active areas of zoning reform nationwide. States like California, Oregon, and Washington have passed legislation overriding local restrictions on ADUs, making them a by-right use in most residential zones. Common regulatory changes include eliminating owner-occupancy requirements, reducing parking mandates, and allowing ADUs on any residential lot.
Why This Matters for CRE
ADU reforms represent a significant shift in residential zoning policy with direct investment implications. Properties in jurisdictions that allow ADUs carry more development potential — and therefore more value — than identical properties in restrictive jurisdictions. For investors, tracking ADU ordinance changes reveals where municipalities are opening the door to incremental density increases. In markets like Los Angeles and Portland, ADU construction has become a meaningful contributor to housing supply and rental income.
What to Watch For
- State-level preemption: State laws that override local ADU restrictions create immediate opportunities across entire markets
- Fee waivers and incentives: Reduced permit fees and expedited review signal strong municipal support for ADU construction
- Rental restrictions: Some jurisdictions still restrict ADU rentals to long-term tenants or prohibit short-term rentals
- Impact on property values: Properties with ADU potential command a premium in markets where ADU construction is active
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