Accessory Dwelling Unit (ADU) Statistics 2026

ADU vs. Assisted Living Cost

ADU Statistics in the United States

How Many Homes in the U.S. Have an ADU?

Approximately 1.4 million properties in the United States have accessory dwelling units, based on MLS transaction data from 1997 to 2019. More than half of those properties are concentrated in four states: California, Florida, Texas, and Georgia. (Freddie Mac Research, 2020)

Nearly 70,000 properties with ADUs were sold in 2019, representing 4.2% of total homes sold on MLS. By comparison, less than 9,000 properties with ADUs were sold in 2000 (1.1% of total). (Freddie Mac Research, 2020)

Shovels, a private permit-data company, reports 2.8 million ADU permit records since 2018; its county ranking covers the 627 counties with at least 100 ADU permits in that period. (Shovels, 2025)

How Fast Are ADUs Growing?

First-time ADU listings on MLS grew 8.6% per year on average from 2009 to 2019. Growth was concentrated in the South and West. Among active for-sale listings on MLS, the share with ADUs rose from 4.3% in 2010 to 9.2% in 2019 in Sun Belt states, compared with 2.7% to 4.1% in Northern states. (Freddie Mac Research, 2020)

Freddie Mac highlighted Portland, Dallas, and Seattle as leading markets for year-over-year growth in first-time ADU listings between 2015 and 2018. Detached ADUs are more common in sprawling Western metro areas, while homeowners in denser East Coast cities are more likely to create attached ADUs through conversion of attics, basements, or garages. (Freddie Mac Research, 2020)

What Percentage of Homeowners Want an ADU?

71% of Americans were unfamiliar with ADUs in a 2023 Freddie Mac consumer survey. Once respondents were provided with a definition, 32% of homeowners who do not currently own an ADU reported interest in having one on their property in the future. (Freddie Mac Consumer Survey, 2023)

The survey also found that about half of homeowners without an ADU believe it would be somewhat to very difficult to create or build one on their current property. Among those interested in building, the most frequently selected financing methods were personal savings and rental income from future tenants. (Freddie Mac Consumer Survey, 2023)

ADU Laws by State

As of April 2026, 18 states had broadly legalized ADUs. Mercatus classifies 10 of those frameworks as strong preemptive laws and 8 as weaker preemptive laws. The most common barriers that still suppress construction are owner-occupancy requirements, parking mandates, and discretionary review. (Mercatus Center, 2025)

What States Allow ADUs?

Eighteen states had broadly legalized ADUs as of April 2026: California, Washington, Vermont, New Hampshire, Oregon, Utah, Connecticut, Maine, Rhode Island, Montana, Arizona, Colorado, Hawaii, Massachusetts, Arkansas, Iowa, Maryland, and Nevada. (Mercatus Center, 2025)

In the remaining states, ADU legality is determined at the city or county level. Some jurisdictions in these states allow ADUs through local ordinance while others prohibit them entirely.

For a complete 50-state comparison table with statute links, policy classifications, and barrier analysis, see our ADU Laws by State guide.

Which States Allow ADUs by Right?

California, Oregon, and Washington all require by-right approval for ADUs that meet their statutory standards. A by-right pathway means homeowners can build an ADU without a conditional use permit, public hearing, or discretionary review — they apply for a building permit and receive approval if the project meets objective standards. States that mandate a by-right pathway see significantly higher ADU production because the process is faster, cheaper, and more predictable. (Mercatus Center, 2025)

Which State Rules Still Block ADU Construction?

Owner-occupancy requirements, parking mandates, and discretionary review are the regulatory barriers most associated with low ADU production. (Mercatus Center, 2025)

California ADU Statistics and Permit Data

California has the best public ADU permit data in the country because every city and county reports annual housing production to the Department of Housing and Community Development. HCD publishes raw APR data from 2018 onward. (California HCD)

How Many ADUs Have Been Built in California?

California permitted 83,865 ADUs through 2022. Annual ADU permitting increased 15,334% from 2016 to 2022, and ADUs accounted for 19% of all housing units produced in the state by 2022. (California HCD Annual Progress Reports; analysis by California YIMBY, 2024)

Which California Cities Have the Most ADU Permits?

Los Angeles leads the nation in ADU production by a wide margin. The city — not the county — accounted for 11,500 of the roughly 26,600 California ADUs permitted from 2017 to 2019 alone. (Accessory Dwellings / Furth, 2021)

San Francisco, Oakland, San Diego, and Sacramento are also among the highest-producing cities. City-level permit data is available through the HCD Annual Progress Report dashboard.

ADU Permits Outside California

Massachusetts reported 1,224 approved ADUs and 1,639 applications in its 2025 statewide ADU survey following the Affordable Homes Act. (Massachusetts Housing and Livable Communities, 2025)

ADU Cost Statistics

How Much Does an ADU Cost to Build?

The median ADU construction cost is $150,000, or about $250 per square foot, based on a California homeowner survey. 37% of projects cost less than $100,000, and 71% cost less than $200,000. 53% of homeowners paid for construction entirely in cash and 43% used bank loans. (UC Berkeley Center for Community Innovation, Implementing the Backyard Revolution, 2021)

ADU Cost per Square Foot

ADU costs per square foot range from $197 to $329 across California regions. (UC Berkeley CCI, 2021)

Source: UC Berkeley Center for Community Innovation, Implementing the Backyard Revolution, 2021. California

ADUs have significant fixed costs — every unit requires a kitchen, bathroom, HVAC system, and utility connections regardless of size. This means smaller ADUs often have a higher cost per square foot than larger ones.

ADU Property Value and Rent Statistics

How Much Value Does an ADU Add to a Home?

In California in 2023, the median appraised value of properties with ADUs was $1,064,000, compared with $715,000 for properties without ADUs. Annualized value growth from 2013 to 2023 was 9.34% for properties with ADUs versus 7.65% for properties without them. (FHFA UAD Aggregate Statistics, January 2025)

The number of purchase appraisals with ADUs in California increased from 3,463 in 2013 to a peak of 9,246 in 2021, before declining to 4,910 in 2023.

How Much Rent Can an ADU Generate?

The median ADU rental price in California is $2,000 per month statewide. Only 8% of new ADUs are used as short-term rentals. (UC Berkeley CCI, 2021; HUD Fair Market Rents)

Are ADUs Mostly Long-Term Rentals?

Yes. Only 8% of new ADUs in California were used as short-term rentals. About half served as income-generating rental units, while others housed relatives or were used as home offices, guest space, or other personal uses. (UC Berkeley CCI, 2021)

Cities With Preapproved ADU Plans

Some cities publish official preapproved plans, homeowner guides, fee reductions, or financing programs. (HUD PD&R, 2025)

Source: Dwelling Index verification of official city government websites, April 2026.

What Is an ADU?

An accessory dwelling unit (ADU) is a smaller, independent residential unit located on the same lot as a primary single-family home. ADUs are also commonly known as granny flats, in-law suites, backyard cottages, secondary suites, casitas, basement apartments, carriage houses, and guest houses.

ADUs can be attached to the primary residence (such as a converted garage or basement), detached (a standalone structure in the backyard), or created within the existing footprint of the home. They include their own kitchen, bathroom, and entrance.

Are Granny Flats, Backyard Cottages, and In-Law Suites the Same as ADUs?

Yes. These are all common names for accessory dwelling units. The terminology varies by region and by how the unit is constructed. Other names include ohana units (Hawaii), laneway houses (Canada), and accessory apartments.

What Is the Difference Between an ADU and a JADU?

In California, a Junior Accessory Dwelling Unit (JADU) is no more than 500 square feet of interior livable space and is contained entirely within a single-family residence. Under California law, homeowners can build both a JADU and a full ADU on the same property. (California HCD, ADU Handbook)

Are ADUs Legal in All 50 States?

No. As of April 2026, 18 states had broadly legalized ADUs statewide. In the remaining states, legality depends primarily on local rules. See the ADU Laws by State section above. (Mercatus Center, 2025)

Sources, Methodology, and Data

Data Sources

How the Statistics Were Calculated

Most statistics on this page are direct extractions from the sources listed above — no modeling or estimation is involved.

For the complete methodology, see Methodology.

Data is licensed under CC BY 4.0 — free to use with attribution to Dwelling Index.