In short
- 80 ADU permits since 2018.
- 15 in 2025.
- Typical permit time: 177 days from application to permit (median of 67 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 | 2 | — | — |
| 2019 | 2 | — | — |
| 2020 | 7 | — | — |
| 2021 | 8 | — | — |
| 2022 | 15 | 0 | 0 |
| 2023 | 14 | — | — |
| 2024 | 17 | — | — |
| 2025 | 15 | — | — |
“—” means the source for that year does not report ADU type.
Read more: ADU types explained
Not counted above: 29 approved projects with no building permit reported yet.
ADU rules in Placentia
State law check: HCD sent a technical-assistance letter (November 27, 2023) telling the city it may not require homeowners' association approval for an ADU permit; no formal findings.
| Rule | Placentia's code | State law guarantees |
|---|---|---|
| Maximum size | Detached: 1,200 sq ft. Attached: 50% of the existing house; with a new house, 850 sq ft (0 to 1 bedroom) or 1,000 sq ft (2+ bedrooms). 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, whichever is lower. | 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; front per the zone unless that blocks an 800 sq ft ADU. Detached ADUs 10 ft from other buildings, with the same exception. None for rebuilds in the same place. | No more than 4 ft side and rear; none for conversions of existing space. |
| Parking | 1 space, tandem allowed, unless exempt (transit, historic district, 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 unless it has its own bathroom, 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 attached ADU and one junior ADU. State-law ADUs (a conversion ADU or junior ADU, or a detached ADU up to 800 sq ft with a junior ADU) can't be combined with other ADUs. | 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 the ADU and the main house. | No guarantee: cities may require rentals of more than 30 days, and junior ADUs can't be short-term rentals. |
- The ADU must match the house's architectural style, and its entrance and stairs shouldn't be visible from the street unless that blocks an 800 sq ft ADU.
- Utilities must be underground.
- The city runs a pre-reviewed ADU plan program, but no plans had been listed when checked.
Where local rules conflict with state law, state law controls. Sources: Placentia Municipal Code chapter 23.73 (amended March 17, 2026) · HCD letter (November 27, 2023); 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 |
|---|---|---|---|
| Junior ADU (JADU) | too few to say | 1 | |
| Unclassified | 182 | 100 – 308 | 66 |
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 44 ADU permits Placentia reported issuing from 2020 through 2023, 34 (77%) 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 Placentia? Feature your business on this page.
Questions about ADUs in Placentia
How many ADUs have been permitted in Placentia?
Public records show 80 ADU permits in Placentia from 2018 through 2025. 15 in 2025. 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 Placentia?
Among the 67 ADU permits in Placentia with both dates recorded, half were issued within 177 days of the application; the middle half took 99 to 308 days. That includes plan-check corrections and resubmittals, not just the review itself.
Can I build an ADU on my property in Placentia?
California law allows ADUs on most lots with a house, including in Placentia, 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 Placentia?
Apply with the City of Placentia's Development Services Department, in person or through the city's SmartGov online 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.