In short
- 422 ADU permits since 2018.
- 58 in 2025, down 36% from 2024.
- Typical permit time: 138 days from application to permit (median of 377 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 | 19 | — | — |
| 2019 | 22 | — | — |
| 2020 | 39 | — | — |
| 2021 | 46 | — | — |
| 2022 | 62 | — | — |
| 2023 | 86 | — | — |
| 2024 | 90 | — | — |
| 2025 | 58 | — | — |
“—” means the source for that year does not report ADU type.
Read more: ADU types explained
ADU rules in Fountain Valley
State law check: HCD found the city's ADU ordinance (October 3, 2023) out of line with state law (December 6, 2024), including its recorded covenant; a code update went to the Planning Commission on April 9, 2025, but the published code hasn't changed.
| Rule | Fountain Valley's code | State law guarantees |
|---|---|---|
| Maximum size | Detached: 850 sq ft, or 1,000 sq ft with more than one bedroom. Attached: 50% of the house (at least 800 sq ft). No cap for conversions. Minimum 150 sq ft. 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: one story, 16 ft (18 ft near transit, plus 2 ft for roof pitch). Attached: 2 stories, 25 ft or the zone limit. | 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; none for conversions. A detached ADU over 800 sq ft sits 10 ft from the house. Windows within 5 ft of a lot line must be high or frosted. | No more than 4 ft side and rear; none for conversions of existing space. |
| Parking | 1 space per new ADU or per bedroom, whichever is less, unless exempt (any bus stop within ½ mile, historic district, car share); none for conversions. No replacement parking for converted garages. | 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 | The code requires ADUs created after January 1, 2025 to be owner-occupied, in a recorded covenant; HCD found that covenant unlawful. Junior ADU: the owner lives in the house or the junior ADU. | 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 | One ADU and one junior ADU, or a converted ADU, a junior ADU and an 800 sq ft detached 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 | More than 30 days, for ADUs and junior ADUs. | No guarantee: cities may require rentals of more than 30 days, and junior ADUs can't be short-term rentals. |
- ADUs must match the house's colors, materials, roof, windows and doors.
- At most two entrances to an ADU, and no separate entrance to a bedroom (not for state-law ADUs).
- No new driveway for ADU parking, except on corner lots with Public Works approval.
Where local rules conflict with state law, state law controls. Sources: Fountain Valley Municipal Code 21.08.055 · HCD findings (December 6, 2024) · Notice of Planning Commission hearing on Code Amendment 25-04 (March 20, 2025); HCD's list of review letters; California ADU rules. Verified Oct 5, 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 | 138 | 0 – 227 | 377 |
Middle half: the range covering the middle 50% of permits (a quarter were lower, a quarter higher).
Read more: How long ADUs take to build
From permit to completion
Of the 223 ADU permits Fountain Valley reported issuing from 2020 through 2023, 165 (74%) have a completion reported to the state. For those, the median time from permit to completion was 8 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 Fountain Valley? Feature your business on this page.
Questions about ADUs in Fountain Valley
How many ADUs have been permitted in Fountain Valley?
Public records show 422 ADU permits in Fountain Valley from 2018 through 2025. 58 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 Fountain Valley?
Among the 377 ADU permits in Fountain Valley with both dates recorded, half were issued within 138 days of the application; the middle half took 0 to 227 days. That includes plan-check corrections and resubmittals, not just the review itself.
Can I build an ADU on my property in Fountain Valley?
California law allows ADUs on most lots with a house, including in Fountain Valley, 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 Fountain Valley?
Apply with the City of Fountain Valley through a building permit application; its Planning Department publishes an ADU standards handout. 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.