In recent years, both state and local housing policy have focused heavily on increasing the supply of accessory dwelling units (ADUs)—small backyard housing units—as a lower-cost housing type. So far, this policy bet appears to be paying off. Between 2020 and 2024, the number of ADUs permitted in San Diego County more than tripled, while the number of ADUs actually completed increased by 480% (see Figure 1), according to a new analysis of state data1 by the Center for Housing Policy and Design (CHPD) at UC San Diego.
The CHPD analysis also found that in 2024:
- Most new ADUs are located in the City of San Diego and Unincorporated San Diego County, though Oceanside, Chula Vista, and Encinitas have also seen significant ADU construction.
- Despite the recent controversy over multi-unit ADUs in the City of San Diego, few ADU projects consisted of more than two ADUs.
- Although they are promoted as an affordable alternative to other housing options, most ADUs are priced at an above-moderate income level. Less than 10% of the ADUs have affordable housing deed restrictions on them. However, ADUs are more likely to be priced at moderate income levels than other housing types.
- According to the state data, the vast majority of ADUs are intended to be rentals at their time of application, although the data cannot confirm whether this is actually happening on the ground once units are completed.
ADUs have been a major focus of state and local policy since 2017, when the state first required that local governments approve ADUs on a ministerial basis, meaning they do not go to a planning commission or an elected body for individual approval. In 2022, the City of San Diego adopted an ADU bonus program, which permits multiple ADUs on single-family lots if some of them are affordable.
The number of ADUs permitted and completed has increased dramatically since 2020.
From 2020 to 2024, the number of ADUs permitted across all jurisdictions within San Diego County has increased by 247%, from 1,150 to 3,991 (see Figure 1). The number of ADUs completed— that is, not just permitted but issued certificates of occupancy— has risen from 342 to 1,984, a 480% increase.
Figure 1. ADUs Permitted and Completed, San Diego County, 2020-2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year.
Most ADUs are found in the City of San Diego and Unincorporated San Diego County.
The City of San Diego permitted the most ADUs of all the jurisdictions in San Diego County (see Figure 2). Unincorporated San Diego County ranked second, followed by Chula Vista, Vista, and Encinitas.
Figure 2. ADUs Permitted by Jurisdiction and Tenure, San Diego County, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year.
The City of San Diego and Unincorporated San Diego County also ranked first and second in ADUs completed, followed by Oceanside, Chula Vista, and Encinitas (see Figure 3).
Figure 3. ADUs Completed by Jurisdiction and Tenure, San Diego County, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year.
Few ADU projects had multiple units.
Despite the recent controversy over bonus ADUs in the City of San Diego, multiple-unit projects made up a small percentage of total ADU projects being permitted and completed in 2024. Of all permitted ADU projects (3,274), 85% (2,796) had one unit, while only 2% (60) had more than two units (see Figure 4). Of the completed projects (1,797), 92% (1,656) had one unit, while 1% (23) had more than 2 units.
Figure 4. Units Per ADU Project Completed and Permitted, San Diego County, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year.
Only one ADU project completed in 2024 had 10 units, a garage conversion located in Oceanside. Seven permitted projects had more than 10 units; these projects ranged from 11 to 18 units, with one outlier, a 36-unit project permitted in the City of San Diego.
Few multiple ADU projects are being built, even in the City of San Diego.
The number of projects with multiple ADUs remains small even in the City of San Diego. Furthermore, most multiple ADU projects in the city appear to be 2 units, as in the rest of San Diego County (see Figure 5).
The City of San Diego permitted more multiple-unit projects than the rest of the region in 2024. Of the city’s permitted projects (1,605), 28% (444) had more than 1 unit. Most of this permitting involves 2-unit projects, as only 4% (58) of permitted projects had 3 or more units.
A slightly higher number of completed 2+ unit ADU projects were located in the City of San Diego than the region at large, with 18% (124 of 687) of ADU projects completed in the city having more than one unit.
Figure 5. Units Per ADU Project Completed and Permitted, City of San Diego, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year.
Most ADU units are priced in the above-moderate range.
ADUs are often framed as a form of affordable housing. However, most ADU units are not affordably priced. Nevertheless, more ADUs appear to be more affordable to households with moderate income than other housing types (see Figure 7).
Of ADUs permitted in 2024, 69% (2,742) were priced above moderate income, based on the HCD affordability calculator, while 20% (786) were priced to households with moderate income, 8% (303) were affordable to those with low income, and just 4% (160) were affordable to those with very low income (see Figure 6).
Completed ADUs in 2024 showed a similar pattern, with 60% (1,193) affordable to renters at an above-moderate income level, 24% (479) affordable to moderate-income renters, and 10% (194) affordable to low-income renters. Just 6% (118) of ADUs completed in 2024 were affordable to households with very low income.
Figure 6. ADUs Completed and Permitted by Affordability Level*, San Diego County, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year. *Income categories as defined by the HCD affordability calculator.
Despite the majority of ADUs being priced at an above moderate income level, completed ADUs were more likely to be affordable to moderate income renters than other housing types. 24% of ADUs completed in 2024 were affordable to moderate-income households compared with only 6% for all housing types (see Figure 7). The percentage of new ADUs affordable to low- and very-low-income households is comparable to the percentage of all housing units affordable to those households.
Figure 7. ADUs versus All Housing Types** Completed by Affordability Level*, San Diego County, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year. *Income categories as defined by the HCD affordability calculator. **”All housing types” includes Single Family Homes, Multifamily Homes (2+ units per structure), ADUs, and Mobile/Manufactured Homes.
Few ADUs featured deed-restricted affordability.
Deed restrictions are a tool jurisdictions use to ensure affordable housing does not get flipped to market-rate. Deed restricted units are required to be rented or sold at a particular price to a household whose income does not exceed a specified amount.
Of nearly 4,000 ADUs permitted in 2024, only 7% (263) had deed restrictions. Of nearly 2,000 ADUs completed in 2024, less than 2% (36) had a deed restriction. Most deed-restricted units were for moderate-income households. APR data does not provide the duration of deed restrictions.
ADUs in the City of San Diego are less likely to be affordable, but more are deed-restricted.
ADUs permitted and completed in the City of San Diego in 2024 were generally less affordable than those in other jurisdictions within the region. Of permitted ADUs located in the city, 95% (813 of 848) of completed and 88% (2,019 of 2,281) of permitted ADUs located in the city were affordable to only households above moderate income (see Figure 8). While just 4% of completed ADUs in the entire county in 2024 were affordable to moderate-income households, that figure was only 2% in the city.
Figure 8. ADUs Completed and Permitted by Affordability Level,* City of San Diego, 2024
Source: 2024 Annual Progress Report, A2 (June 30th, 2025), distributed by the California Department of Housing and Community Development, https://data.ca.gov/dataset/housing-element-annual-progress-report-apr-data-by-jurisdiction-and-year. *Income categories as defined by the HCD affordability calculator.
The City of San Diego, however, leads the region in deed restricting ADUs to preserve affordability. All but one of the 263 permitted units, and 36 completed units with deed-restrictions were located in the City of San Diego. Almost all deed restricted units were for middle income households. In the city, 92% (240 of 262) of permitted units with deed restrictions, and all except one of the completed units with deed restrictions, were priced for moderate income.
Many ADUs may not be placed on the rental market.
The majority of ADUs that were permitted and completed in 2024 were proposed to be renter-occupied rather than owner-occupied in their initial entitlement application (see Figures 1 and 2). However, APR data does not tell us whether units were indeed owner—or renter—occupied at their completion or if they were actually placed on the rental market. More research, which goes beyond APR data, is needed to determine the uses of ADUs and their true impact on the rental market.
1 This analysis is based on the APR Table A2 pulled from the California Open Data Portal on 7/17/2025. The Department of Housing and Community Development (HCD) releases data yearly from the Annual Progress Reports (APR) jurisdictions are required to submit to them. These Annual Progress Reports1 include records of all housing units permitted, meaning a jurisdiction has approved the project, and units issued a certificate of occupancy, meaning the jurisdiction has inspected a completed project. APR data is imperfect as it is self-reported, both by the homeowner or developer to the jurisdiction, and then by the jurisdiction to HCD. Nonetheless, it remains a useful tool to track what housing projects jurisdictions are permitting and seeing built.
