ADU Feasibility Quiz

Since California passed AB 68 and SB 9, nearly every single-family lot in Orange County is legally eligible for at least one ADU. That doesn't mean every lot is practically feasible. Six factors determine whether an ADU project makes sense on your specific parcel: lot size and shape, setback requirements, existing structure placement, utility access, intended use, and HOA or overlay restrictions specific to your city.

The biggest source of surprise for homeowners is usually the cost gap between their mental model and reality. A detached 600 sq ft ADU in a median Orange County neighborhood costs $200,000–$300,000 all-in once you include design, permits, site work, utility connections, construction, and finishes. Garage conversions are the budget-friendly alternative at roughly half that cost because the existing structure does most of the heavy lifting. Attached ADUs land in the middle.

City-specific rules matter more than people expect. Costa Mesa and Irvine are the fastest OC cities for ADU permits (60 days or less for streamlined review). Newport Beach coastal-zone parcels can take 14–20 weeks because of Coastal Commission review. Mission Viejo and Lake Forest are HOA-heavy, meaning your village or master association has to approve the plans before the city will even accept your permit application. The quiz factors all of this in when generating your verdict.

Use this quiz as a planning tool, not a final answer. For a detailed assessment of your specific parcel including precise setbacks, zoning overlays, and utility service verification, schedule an ADU feasibility consult.