Westminster Offers 18 Preapproved ADU Plan Combinations — but They Are Not Building Permits

WESTMINSTER, Orange County — October 23, 2026. Homeowners comparing backyard homes have an unusually detailed city-designed option: Westminster offers six preapproved accessory dwelling unit (ADU) floor plans, each with three different roof designs, producing a total of 18 plan combinations. The options are published on the city’s ADU Standard Plan Program page. Although the structural designs have been pre-reviewed, the city says plainly that these are not pre-permitted.

What sizes are available?

The standard designs range from 748 to 1,198 square feet. Options include two-bedroom, three-bedroom and four-bedroom detached units, with one- or two-bathroom layouts depending on the plan. Each has a choice of gabled roof construction or a hipped truss roof. Plan square footage in the city chart is stated as net interior floor area, so a construction estimate and site plan must use the city’s actual measurement rules.

What work is still required?

Homeowners must engage qualified designers or engineers for site-specific drawings, including the proposed plot plan and information about the existing main home. The city’s program links separate guides identifying which drawings are preapproved and which technical forms remain required. Drainage, flood zone conditions, utility connections, easements and existing structures can affect feasibility or require engineering changes.

Can plans be filed online?

Yes. The city offers the Westminster Build Online Portal for application submission. Its general ADU application guide identifies review by Planning, Building and Engineering. A complete package is checked before a construction permit may be issued, and inspections occur during work. A designer’s statement that construction can start immediately because a drawing is city-approved should be independently verified.

How much does it cost?

Westminster makes an ADU standard-plan fee sheet and checklist available online. Those materials are the correct starting point for a municipality-specific estimate, but owners should also price foundation, trenching, water and sewer service, electrical work, applicable school fees, contractor labor and inspections. A design that reduces architectural work does not eliminate all other project expenses.

Who should be contacted?

For a specific lot, request a current eligibility and code check from Westminster Planning at 714-548-3247 or planning@westminster-ca.gov. Ask whether the published standard plan set has been updated for the building-code cycle in effect in 2026 and whether use of a plan requires a liability waiver.

Read Westminster News and Santa Ana News. Submit corrections to California58 Newsroom. Support independent housing reporting.

Sources: City of Westminster Preapproved ADU Standard Plan program, city ADU application guide and official permit materials. This is independent explanatory reporting, not a permit or contractor estimate.

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