In short
- 811 ADU permits on record, nearly all since 2020.
- 137 in 2025, down 36% from 2024.
- Typical permit time: 173 days from application to permit (median of 741 permits with both dates recorded).
About this data
- Source: California HCD Housing Element Annual Progress Reports. The state data does not say whether an ADU is detached, attached, a garage conversion or a JADU, so most records show as 'unknown'. Permit valuations are not published in this source. Timelines use the application date the city reported to the state, matched to the permit where possible; some cities report their planning application date, so timelines can include planning review. Each project is counted once, in its building-permit year (or completion year when no permit date was reported).
Permits by year
Permits by year and type (table)
| Year | All ADU permits | Garage conversions | Detached |
|---|---|---|---|
| 2018 | 3 | — | — |
| 2019 | 16 | — | — |
| 2020 | 52 | — | — |
| 2021 | 110 | — | — |
| 2022 | 134 | — | — |
| 2023 | 145 | — | — |
| 2024 | 214 | — | — |
| 2025 | 137 | — | — |
“—” means the source for that year does not report ADU type.
Read more: ADU types explained
ADU rules in Downey
State law check: No HCD review letter on file (that isn't a finding either way). The city replaced its ADU rules in April 2025 and amended them in June 2026.
| Rule | Downey's code | State law guarantees |
|---|---|---|
| Maximum size | 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms); attached 50% of the house or 800 sq ft, whichever is more, up to 1,000. Conversions no cap. Junior ADU 500 sq ft. | At least 850 sq ft (1,000 sq ft with 2+ bedrooms) must be allowed; an 800 sq ft detached ADU always is. Conversions of existing space have no size cap. Junior ADU: up to 500 sq ft. |
| Height | Detached: 16 ft (18 ft near transit, plus 2 ft for roof pitch). Attached: 25 ft or the zone limit. No more than 2 stories. | Detached: at least 16 ft (18 ft within ½ mile of transit, plus 2 ft for a matching roof). Attached: 25 ft or the zone's limit, whichever is lower. |
| Setbacks | 4 ft side and rear; not in the front setback unless an 800 sq ft ADU won't fit elsewhere. Conversions keep existing setbacks. | No more than 4 ft side and rear; none for conversions of existing space. |
| Parking | 1 uncovered space per ADU (driveway or tandem is fine) unless exempt (transit, conversions, car share and others). | At most 1 space; none within ½ mile of transit and in several other cases. No replacement parking when a garage is converted. |
| Owner living on site | None for ADUs. Junior ADU: only when it shares a bathroom with the house, with a deed restriction. | None for ADUs. A junior ADU that shares a bathroom with the house requires the owner to live in one of them. |
| How many on a single-family lot | Up to two ADUs (one new attached or detached, one converted) and one junior ADU. | One ADU converted from existing space, one junior ADU and one new detached ADU (up to 800 sq ft). From January 1, 2027: two new detached ADUs (a city then needn't allow a junior ADU on that lot). |
| Short-term rentals | Not for less than 30 days. | No guarantee: cities may require rentals of more than 30 days, and junior ADUs can't be short-term rentals. |
- Design standards: covered entry facing the street, materials and roof slope matching the house, frosted glass on second-story ADUs, enclosed stairs, no second-floor balconies.
- No impact fees on ADUs up to 750 sq ft.
- The city is building a pre-approved detached ADU plan program; none were available as of July 28, 2026.
Where local rules conflict with state law, state law controls. Sources: Downey Municipal Code §§ 9414–9414.20 (Ord. 25-1523, 2025; Ord. 26-1544, Jun 9, 2026); HCD's list of review letters; California ADU rules. Verified Sep 30, 2026. Rules change and every lot is different: confirm with the city before you design.
How long permits take
| Type | Median days, application to permit | Middle half | Permits |
|---|---|---|---|
| Unclassified | 173 | 112 – 273 | 741 |
Middle half: the range covering the middle 50% of permits (a quarter were lower, a quarter higher).
Read more: How long ADU permits take in Los Angeles (and other cities) · How long ADUs take to build
From permit to completion
Of the 427 ADU permits Downey reported issuing from 2020 through 2023, 256 (60%) have a completion reported to the state. For those, the median time from permit to completion was 9 months.
The state reports don't record expired or cancelled permits, and a completion the city hasn't reported looks the same as an unfinished project, so the share is a floor. Years with incomplete reports are left out.
What neighbors declared as cost
Cost data (declared permit valuations) is not published for this area in these sources.
Read more: How to choose an ADU builder
An ADU builder serving Downey? Feature your business on this page.
Questions about ADUs in Downey
How many ADUs have been permitted in Downey?
Public records show 811 ADU permits in Downey through 2025, nearly all since 2020. 137 in 2025, down 36% from 2024. These counts come from the city's reports to the state, which place a project in its completion year when no permit date was reported.
How long does an ADU permit take in Downey?
Among the 741 ADU permits in Downey with both dates recorded, half were issued within 173 days of the application; the middle half took 112 to 273 days. That includes plan-check corrections and resubmittals, not just the review itself.
Can I build an ADU on my property in Downey?
California law allows ADUs on most lots with a house, including in Downey, but what you can build depends on your lot, local rules and utilities. This site shows permits, not eligibility. See California ADU rules.
Where do I apply for an ADU permit in Downey?
Apply with the City of Downey's Community Development Department: a Planning site-plan review through the Accela Citizen Access portal, then a Building Division permit. Official ADU page.
How current is this?
- State annual progress reports: through 2025 (published once a year)
How our data works · Download the data · Free to reuse with credit to SoCal ADU Tracker (socaladutracker.com), under CC BY 4.0.