Building an ADU in Orange, CA
One city, two very different games: a standard state-law path on most lots — and four historic districts where your ADU needs a preservation professional before the city will look at it.
Orange ADU key facts
| Who reviews your plans | The City of Orange’s own Planning Division — with extra submittal rules inside its historic districts |
| The address question | Orange has four historic districts (Old Towne among them); inside one, an ADU triggers historic-preservation review |
| What that review needs | A report by a qualified historic-preservation professional plus conformance with the Old Towne design standards and a Minor Design Review application |
| Outside the districts | The normal state-law path: ministerial approval, 4-ft setbacks, the 2026 review clock |
In Orange, the first question isn’t what you want to build — it’s where your lot sits. The city maintains four historic districts, including Old Towne, and its submittal rules are explicit: additions, infill and accessory dwelling units on property in a historic district require an evaluation prepared by a qualified historic-preservation professional, conformance with the Old Towne Historic Preservation Design Standards, and a Minor Design Review application. Outside the districts, Orange is a normal state-law city. Same town, two different projects — so we check the address before anything else.
How many ADUs actually get built in Orange
Orange issued building permits for 88 ADUs in 2025, and 459 in total since 2018. These are the city’s own figures, filed with the State of California — not an estimate.
| Year | ADU building permits issued in Orange |
|---|---|
| 2018 | 10 |
| 2019 | 10 |
| 2020 | 39 |
| 2021 | 56 |
| 2022 | 83 |
| 2023 | 69 |
| 2024 | 104 |
| 2025 | 88 |
For scale: ADUs were 33.7% of every home permitted in Orange County in 2025 — about one in every three — and 25.9% of every home permitted statewide. Full city-by-city tables are on our California ADU statistics page.
Source: California Department of Housing and Community Development, Housing Element Annual Progress Report, Table A2 — units with building permits issued. Retrieved August 2026.
An ADU we are building in Orange right now
This one is on our boards as you read this. The slab was poured on 12 August 2026, the roof was framed by 15 August, and by 29 August the walls, interior partitions and rough electrical were in. Three weeks, our own crew, our own photos.
What’s different about building in Orange
If your lot is in a historic district, respect the process and it works. The city wants the new unit to sit quietly behind the historic house — materials, massing and rooflines that defer to the original structure — and it asks for a preservation professional’s report (the city keeps a list of qualified consultants) before plan check. That adds design time and a consultant fee, but it is not a veto: state ADU law still applies, and a well-designed rear-yard unit gets through. The mistake that costs money is submitting a standard plan set first and discovering the historic requirements as a correction.
Outside the four districts, Orange behaves like its neighbors: ministerial approval for a code-compliant unit, 4-foot side and rear setbacks, and the state review clock — 15 days to completeness, 60 days to a decision. The housing stock is a mix, from early-1900s bungalows near the core to postwar tracts further out, so the usual physical checkpoints — slab, panel, sewer run — decide the budget.
One planning note we give every Orange homeowner: if you are anywhere near a district boundary, don’t guess. The city’s maps are precise, the submittal requirements change completely across that line, and confirming it takes us minutes on the first visit.
What an ADU costs in Orange
Published ranges apply in Orange: garage conversions typically $90,000–$150,000, detached units $200,000–$450,000+. In a historic district, add the preservation consultant’s report and design-review time to the plan — a real line item, not a rounding error. Details in the cost guide.
Frequently asked questions
Can I build an ADU in Old Towne Orange?
How do I know if my Orange property is in a historic district?
Does an ADU in Orange need a public hearing?
What does the historic-district requirement cost?
How many ADUs are permitted in Orange each year?
Useful links for Orange homeowners
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