Building an ADU in Westminster, CA
A pre-approved standard-plan program, an online submittal portal, and the heart of Little Saigon — Westminster has quietly modernized its ADU counter.
Westminster ADU key facts
| Who reviews your plans | Westminster’s Planning Division — with ADU plan-check submittal available through the city’s online Build portal |
| Pre-approved plans | The city runs a Preapproved ADU Standard Plan program — pre-approved, but explicitly not pre-permitted: full plan check still applies |
| The fine print | Even with a standard plan, the city requires licensed professionals for the site-specific documents |
| State-law floor | Ministerial approval, 4-ft setbacks, and the 2026 SB 543 review clock all apply |
Westminster has done two modern things with its ADU process: it publishes a Preapproved ADU Standard Plan program, and it accepts ADU plan-check submittals through its online Build portal — no counter queue required. The city is also refreshingly honest about the catch, stating outright that pre-approved plans are not pre-permitted: a complete plan check and site-specific technical documents by licensed professionals are still required. That honesty matches how we quote, which is why we like building here.
What’s different about building in Westminster
Use the standard-plan program for what it really is: a head start on architecture, not a skip-the-line pass. The city’s own language is clear — preapproved plans still go through full plan check, and your foundation, utility routing and setbacks still need licensed site-specific work. Where a standard plan fits your lot, it saves genuine design time; where it doesn’t, a custom design avoids forcing a plan onto a lot that resists it. We price both paths against your property and recommend one.
The online portal is a quiet advantage. Submitting plan check digitally means corrections and resubmittals move without counter visits — on a well-prepared package, that trims dead days out of the calendar. Our submittals go in complete, because the review clock only starts when the city deems the application complete.
And Westminster is the capital of Little Saigon — a community where multigenerational living is normal and backyard homes make immediate sense. Like the city itself, we serve homeowners in more than one language: our team runs projects in English, Mandarin and Cantonese, and we’re used to family decisions made around a bilingual kitchen table. The housing stock — flat postwar lots, detached garages — gives both conversion and detached paths real room.
What an ADU costs in Westminster
Published ranges apply in Westminster: garage conversions typically $90,000–$150,000, new detached units $200,000–$450,000+ — flat lots keep foundations simple. Get a range for your size in the ADU cost calculator.
Frequently asked questions
Does Westminster have pre-approved ADU plans?
Can I submit my Westminster ADU application online?
Can I convert my garage in Westminster?
Does a Westminster ADU need a public hearing?
Useful links for Westminster homeowners
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