The honest answer up front
A typical California garage conversion ADU takes 18 to 22 weeks from the first homeowner call to a certificate of occupancy. That is roughly 4 to 5 months. New detached construction takes longer (typically 7 to 10 months) because it includes foundation, framing, and a full new roof. Garage conversions go faster because the slab, walls, and roof already exist.
Here is what each of those weeks actually looks like.
Weeks 1 to 2: Discovery and design start
What happens:
- Free in-home consultation
- Property and zoning lookup
- Preliminary site measurement and photo survey
- Layout concept and material direction discussion
- Signed design–build agreement
What can delay it:
- Waiting more than a few days between calls
- Indecision on whether to add bedroom or keep open studio
- Title questions or HOA review
Weeks 3 to 6: Plans and engineering
What happens:
- Full architectural drawings: site plan, floor plan, electrical, plumbing, elevations
- Title 24 energy compliance report
- Structural engineering for the converted walls, header at the garage door opening, and roof tie-ins
- Existing main house panel evaluation for ADU electrical service
What can delay it:
- An undersized 100-amp main panel that needs replacement (a 100-to-200 amp upgrade is common)
- Sewer lateral that needs camera inspection
- An older garage with no foundation, only a thickened slab edge — requires a structural retrofit plan
Weeks 7 to 12: City permit submittal and plan check
What happens:
- Submit complete plan set to the city
- City planner reviews zoning compliance — setbacks, height, parking, fire access
- Building department reviews structural, energy, and life-safety
- Corrections issued — typically one or two rounds, occasionally three
- Permit fees paid, building permit issued
Typical jurisdiction timelines for garage conversions:
- Anaheim, Santa Ana, Long Beach, Pasadena: 4 to 6 weeks
- Most of Los Angeles City: 6 to 10 weeks
- Irvine, Newport Beach, smaller OC cities: 4 to 6 weeks
- LA County unincorporated: 8 to 12 weeks
- Cities in the Inland Empire vary widely
What can delay it:
- An expediter on the contractor side instead of in-house permitting
- Slow homeowner sign-off on correction responses
- Holiday closures (December and major holiday weeks add a full week)
Weeks 13 to 14: Pre-construction
What happens:
- Final material selections — flooring, cabinets, countertops, fixtures, paint
- Permit pickup and site preparation
- Utility coordination (gas meter, electrical service upsize if needed)
- Homeowner pre-construction meeting, schedule walkthrough, neighbor courtesy notification
What can delay it:
- Changes to material selections after the order has been placed
- Surprise utility issues discovered at pickup
Weeks 15 to 20: Construction
This is where the garage actually becomes an ADU.
Week 15 — Demo and rough-in. Remove the garage door and frame in the new exterior wall. Cut the slab for new plumbing drains and any new electrical conduit. Trench from the main house panel for the new ADU sub-feed.
Week 16 — Framing and exterior closure. New interior partition walls go up. The header at the former garage door opening is set. New windows and exterior door installed. The exterior gets stucco prep or siding patching where the garage door used to be.
Week 17 — MEP rough-in and inspection. Plumber roughs the kitchen and bathroom drains, vents, and water lines. Electrician runs all wiring. HVAC contractor installs the mini-split line set. City inspectors visit for the framing, electrical, plumbing, and mechanical rough inspections. All four typically pass within the week.
Week 18 — Insulation and drywall. Wall and ceiling insulation goes in. Drywall hung, taped, mudded, primed, painted.
Week 19 — Cabinets, finish, and fixtures. Cabinets and countertops installed. Flooring laid. Plumbing and electrical fixtures set. Bathroom tile complete. Trim and doors hung. Stucco patch finished and painted.
Week 20 — Final cleanup and punch list. Appliances connected. Final cleaning. Homeowner walkthrough. Final inspections scheduled.
Weeks 21 to 22: Final inspection and certificate of occupancy
What happens:
- Building, electrical, plumbing, and mechanical final inspections
- Title 24 energy verification
- Final addressing assigned by the city
- Certificate of Occupancy issued
- Homeowner keys handed over
- Optional: tenant marketing photos and listing prep
What can delay it:
- Punch list items not closed before the inspector arrives
- City inspector schedule backup
- An open landscaping or grading requirement
What pushes the schedule longer
The most common reasons garage conversions take 6 months instead of 4 to 5:
- HPOZ or coastal commission overlay — adds 6 to 12 weeks of design review
- Sewer or panel surprises discovered mid-project
- Material changes after the contractor has already ordered
- Cash flow timing that holds up a milestone payment
- Out-of-town owner who is slow to respond to questions
- Permit corrections taking more than two rounds — usually a sign the original submittal was incomplete
How Vision ADU keeps garage conversions on schedule
Our in-house permitting team submits complete plan sets and responds to city corrections within 48 hours, which is the single biggest schedule lever on any garage conversion. We also pre-order long-lead items (windows, custom cabinets, the electrical panel if it needs upsizing) during the permit phase so they arrive on day one of construction rather than three weeks in.
Related: ADU Permit Guide — Los Angeles, ADU Permit Guide — Orange County, and our garage conversion service page.
FAQ
How long does a garage conversion ADU take in California?
Typical project finishes in 18 to 22 weeks from first call to certificate of occupancy. The actual construction portion is roughly 6 weeks; design, permits, and pre-construction account for the rest.
What is the fastest a garage conversion can finish?
With pre-approved plans and an aggressive city, we have closed projects in 12 weeks. That requires a homeowner who responds within hours, no panel upgrade, no plan corrections, and pre-stocked materials.
What is the single biggest cause of delay?
Plan corrections that take multiple rounds. Submitting a complete, well-prepared plan set on the first pass — including the Title 24 report, structural calcs, and energy compliance — removes the largest schedule risk.
Do I need to upgrade my electrical panel for a garage conversion?
Often yes. Many homes built before 1980 have a 100-amp main panel that cannot carry the additional ADU load. Upgrading to 200 amps typically adds 1 to 2 weeks and is best handled during the permit phase.
Can I live in the main house during the garage conversion?
Yes. Garage conversions are minimally disruptive to the main house. Brief utility shutoffs during the panel upgrade and the new water line tie-in.
Do I need a foundation under the existing garage slab?
Most existing garages have a thickened slab edge that is structurally adequate. Some pre-1960 garages need a foundation retrofit. An evaluation during week 3 to 6 catches this.
Will the inspector require fire sprinklers in a garage conversion?
California ADU law exempts most ADUs from sprinkler retrofits if the main house does not have them. Some cities try to require them anyway — your contractor should push back with the state law citation.