Why garage conversions are the most popular ADU type
A garage conversion reuses an existing foundation, walls, and roof. That keeps cost down, schedule short, and risk low. California state law also exempts garage conversions from replacement parking requirements in most cases, which removes one of the biggest cost surprises.
The 6-step permit process
Step 1: Confirm eligibility
Verify your garage is legal (built with permits) and that your lot zoning allows an ADU. Almost every single-family lot in California does.
Step 2: Hire a designer or use a pre-approved plan
Your converted garage needs:
- Insulation in walls and ceiling
- Heating and cooling
- A bathroom
- A kitchen
- Egress windows in any bedroom
- Title 24 energy compliance
Step 3: Submit to building department
Plans go to your city's building department for plan check. Garage conversions typically clear plan check in 4-8 weeks (faster than new construction).
Step 4: Pay permit fees
Soft costs include building permit, mechanical, electrical, and plumbing permits, plus any school district fees. These vary by city.
Step 5: Construction with inspections
Standard inspection sequence: foundation (if any modifications), rough framing, rough electrical/plumbing/mechanical, insulation, drywall, final.
Step 6: Certificate of occupancy
Once the final inspection passes, your converted garage is a legal dwelling unit.
Common reasons garage conversion permits get rejected
- Existing garage was built without permits.
- Garage encroaches on setbacks or easements.
- Existing electrical service is undersized.
- Existing roof and walls cannot meet current code without major reinforcement.
A pre-construction walkthrough with an experienced ADU builder catches all four before you submit.
What about parking?
State law removes the requirement to replace garage parking when converting to an ADU, as long as your lot is within a half mile of public transit or in certain other categories. Most Southern California cities fall under this exemption.
Related reading
Frequently asked questions
How long does a garage conversion permit take? Plan check typically 4-8 weeks, construction 8-14 weeks.
Can I convert a detached garage? Yes — converting a detached garage creates a detached ADU.
Do I need to upgrade my electrical panel? Often yes. A garage conversion adds significant new electrical load.