How Long Does an ADU Take? California Timeline From Plans to Keys

From the first sketch to handing over the keys, most California ADU projects take about nine to twelve months.

Every homeowner asks the same first question: how long will this actually take? Here is a realistic California timeline, phase by phase, so you can plan around real dates — rental income, a family move-in, or a loan — instead of guesses.

Phase 1: Design and Site Planning — About 4 to 8 Weeks

Design and site planning usually take four to eight weeks. We measure your lot, check setbacks and access, look at utilities, and shape a plan that fits your property and your budget. Projects move through this phase fastest when decisions — bedrooms, laundry, rental or family use — are made early, before engineering starts.

Phase 2: Permits — Most Projects Clear in About 2 to 4 Months

Permits are the part that feels longest. Under California state law, cities have up to 60 days to respond to a complete ADU application, and most of our projects clear permitting in about two to four months, including plan-check corrections. The catch: the 60-day clock only runs on a complete submittal. An incomplete application resets it, which is why getting the submittal right the first time is the single biggest schedule saver. Our ADU FAQ page covers the permit steps in detail.

Phase 3: Construction — 3 to 4 Months for a Garage Conversion, 5 to 7 for a Detached ADU

• Garage conversions finish fastest — about 3 to 4 months — because the walls, roof, and foundation already exist.
• A detached ADU typically takes about 5 to 7 months from foundation to final inspection, depending on utility work — sewer, water, and electrical runs — and the level of finishes you choose.
• Attached ADUs land in between, sharing a wall and some systems with the main home.

The Total: About 9 to 12 Months From Plans to Keys

Add the phases together and most homeowners are looking at about nine to twelve months from plans to keys. A straightforward garage conversion on an easy lot can beat that; a detached build with utility upgrades or a slow plan-check queue can run longer. What moves the schedule most is not the floor plan — it is submittal quality, utility conditions found early instead of late, and how quickly finish decisions get made. At ADU Cities we manage every step in-house, so your timeline stays honest from day one.

Timelines are typical ranges for permitted ADU projects in California and vary by city, project type, and site conditions. The 60-day permit response window applies to complete applications under California state law.

Work With ADU Cities

One Contractor for Every Month of That Timeline

The schedule above only holds when one team owns design, permits, and construction. See how ADU Cities runs your whole project as your ADU contractor in Southern California — one contract, one point of accountability.