A garage conversion is often the fastest and least expensive way to add an ADU, because the foundation, walls and roof already exist. It still has to become a real home: insulated, ventilated, plumbed and approved by the city. IronNest has built four ADUs so far; this is how the process works.
1. Feasibility
- Is the slab sound and level enough to finish over?
- How far is the sewer line, and does it run downhill to it?
- Can the electrical panel carry a second kitchen, or does it need an upgrade?
- Will removing the garage affect required parking? California law limits how cities can require replacement parking for garage conversions.
2. Design
A floor plan with a kitchen, a bathroom and at least one sleeping area, plus windows for light and emergency escape. The garage door opening usually becomes a wall with a window or a door.
3. Permits
ADUs need a building permit. Under state law, a city must approve or deny a complete ADU application within 60 days, and impact fees are waived for units under 750 square feet.
4. Construction
- Framing the old door opening and any new walls
- A raised floor or a moisture barrier and insulation over the slab
- Rough plumbing, including the sewer connection
- Electrical, often with a sub-panel
- Insulation to meet the Title 24 energy code
- Drywall, flooring, kitchen, bathroom and finishes
5. Final Inspection
The city inspects each stage and signs off at the end. Only then is the unit legal to live in or rent.
Cost
Garage conversions typically cost much less than a detached ADU, but the condition of the slab, the distance to the sewer and the electrical service can move the price significantly. A site visit gives you a written fixed price.
More on our ADU construction page.
Common Surprises in Garage Conversions
- A slab that slopes toward the old garage door and needs levelling
- No footing under the garage door opening, so a new one is needed for the infill wall
- An electrical panel without room for new circuits
- A sewer line that is farther or shallower than expected
- Water heaters or laundry in the garage that must be relocated
Each of these is checked at the first visit so it is in the written price.
Making a Small Space Work
- An open kitchen and living area to maximise light
- A compact laundry closet
- Built-in storage and a well-planned bathroom
- Windows placed for light and privacy from the main house
- A heat pump for efficient heating and cooling
Thoughtful design makes a converted garage feel like a small home rather than a converted garage.
IronNest has branches in San Francisco and Sacramento, so a project manager is never far from your job. Book a free site visit and we will walk the space with you.
Common Questions
Do I need to replace the parking I lose?
California law limits when a city can require replacement parking for a garage converted to an ADU. Local details vary, so we confirm the rules for your address during feasibility.
Can I keep part of the garage?
Sometimes. A partial conversion can leave storage or a smaller garage space, depending on the layout and local rules.
How long does a garage conversion take?
Design and permits come first, then several months of construction depending on scope. You receive a written schedule with your proposal.
