How Long Does It Take to Build an ADU in Ventura County?

Design typically runs 3 to 6 weeks, permitting 4 to 12 weeks or longer depending on jurisdiction and review cycles, and construction 3 to 6 months depending on scope. Permitting is the part with the least predictability and the part worth starting earliest.

Design: 3 to 6 weeks

Property and zoning research, early layouts, developed design, then construction documents. Most of the variability here is how quickly decisions get made.

Permitting: 4 to 12 weeks or longer

• The jurisdiction. Thousand Oaks works to a ministerial review target for complete applications. Unincorporated county projects involve more departments and generally take longer.
• How complete the submitted package is.
• Whether additional approvals apply. An Oxnard Coastal Development Permit is its own process.
• Whether the site needs engineering, soils, drainage or septic review.
• How many correction cycles the plans go through.

Construction: 3 to 6 months

A garage conversion with utilities nearby sits at the short end. A detached unit needing a new foundation, a long utility trench and grading sits at the long end.

The things that actually cause delay

• Starting permitting late.
• An incomplete submittal that triggers avoidable correction rounds.
• Changes after permit issuance.
• Utility service connections, which run on their own timeline.
• Discovering an unpermitted existing structure partway through.

More on ADU permitting and ADU construction.

ADU laws and local requirements can change. Information on this page is general and is not a guarantee that a specific project will be approved. Confirm current requirements for the property and jurisdiction before making project or financial decisions.