In short
- 516 ADU permits since 2018.
- 128 in 2025, up 52% from 2024.
- Typical permit time: 317 days from application to permit (median of 19 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 | 5 | 1 |
| 2019 | 40 | — | — |
| 2020 | 51 | — | — |
| 2021 | 74 | — | — |
| 2022 | 54 | — | — |
| 2023 | 66 | — | — |
| 2024 | 84 | — | — |
| 2025 | 128 | — | — |
“—” means the source for that year does not report ADU type.
Read more: ADU types explained
ADU rules in Fullerton
State law check: No HCD review letter on file; that is not a finding of compliance.
| Rule | Fullerton's code | State law guarantees |
|---|---|---|
| Maximum size | Attached: 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms). Detached: 1,200 sq ft. No cap inside the house. 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, 2 stories at most. | 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, street side and rear; front per the zone. None for conversions or rebuilds in the same place. | No more than 4 ft side and rear; none for conversions of existing space. |
| Parking | 1 space unless the ADU is a studio or exempt (transit, historic district or preservation zone, inside existing space, permit parking, car share, built with a new home). No replacement parking. Junior ADU: none. | 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: the owner lives in the house or the junior ADU, 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 | One ADU and one junior ADU. R-1 and R-2 lots of 1 acre or more with a house may add two detached ADUs, or one attached and one detached. | 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 | 31 days or more, 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. |
- Exterior materials and colors must exactly match the house, and the roof slope must match.
- New ADUs are barred in areas the city engineer maps as short on water or sewer service (not state-law ADUs).
- The city adopted its current ADU rules on June 17, 2025 (Ordinance No. 3343).
Where local rules conflict with state law, state law controls. Sources: Fullerton Ordinance No. 3343, FMC 15.17.100 (June 17, 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 |
|---|---|---|---|
| Detached ADU | not reported | ||
| Garage conversion | too few to say | 1 | |
| Unclassified | 324 | 171 – 446 | 18 |
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 245 ADU permits Fullerton reported issuing from 2020 through 2023, 209 (85%) have a completion reported to the state. For those, the median time from permit to completion was 12 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 Fullerton? Feature your business on this page.
Questions about ADUs in Fullerton
How many ADUs have been permitted in Fullerton?
Public records show 516 ADU permits in Fullerton from 2018 through 2025. 128 in 2025, up 52% 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 Fullerton?
Among the 19 ADU permits in Fullerton with both dates recorded, half were issued within 317 days of the application; the middle half took 160 to 437 days. That includes plan-check corrections and resubmittals, not just the review itself.
Can I build an ADU on my property in Fullerton?
California law allows ADUs on most lots with a house, including in Fullerton, 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 Fullerton?
Apply with the City of Fullerton's Community and Economic Development Department (Planning and Building and Safety), which takes building permits online through its EasyDev portal. 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.