An ADU garage combines a functional two-car garage on the ground floor with a complete livable apartment above. For beginners, this is one of the most structured ADU builds available β the configuration is well-established, permit-ready plan sets exist for exactly this program, and the income potential is immediate once construction is complete.
Here is what the process actually looks like, from first steps to final occupancy.
Step 1: Confirm Your Lot Can Support an ADU Garage
Before designing anything, verify your zoning allows this structure. Contact your local planning or building department and ask specifically about:
- Whether detached ADUs are permitted in your zoning district
- The maximum square footage allowed for an accessory structure on your lot
- Required setbacks from property lines β typically 5 feet minimum, but this varies significantly by jurisdiction
- Lot coverage maximums: the percentage of your lot that can be covered by all structures combined
- Whether you are required to live on the property to legally rent out the ADU
- Parking requirements β some jurisdictions require an additional off-street parking space when adding an ADU
Several states β California, Oregon, Washington, and Texas β have passed legislation significantly expanding ADU rights in recent years. Even so, always verify with your specific city or county, not just state law. Local ordinances can be more restrictive than state minimums.
Step 2: Select a Permit-Ready Plan Set
The design phase is where most beginners lose months of time and significant money. Hiring an architect to design an ADU garage from scratch typically costs $8,000β$20,000 and takes four to six months before you even begin permitting.
Starting with a permit-ready plan set gives you a professionally drawn, fully engineered architectural package that is ready for your local building department. Your local architect or engineer reviews the plans, stamps them for your jurisdiction, and makes any site-specific modifications β a process that takes weeks rather than months.
Our ADU garage plans range from the compact 22' x 22' ADU Garage Loft (960 SF total) to the two-bedroom 28' x 28' ADU Garage Loft (1,568 SF) β each including permit-ready architectural drawings for both the garage and apartment levels, printed at full architectural scale.
Step 3: Build a Realistic Budget
ADU construction costs vary significantly by region. For a detached garage-apartment structure, expect a range of $150β$300 per square foot for the livable portion, with the garage level typically costing less per square foot than finished living space. A 1,200 SF total structure (600 SF garage, 600 SF apartment) might run $120,000β$200,000 all-in at midrange construction quality.
Budget line items to account for:
- Site prep and foundation
- Framing and exterior envelope
- Roofing, windows, and exterior doors
- Rough plumbing, electrical, and HVAC
- Insulation and drywall
- Kitchen and bath finishes
- Flooring and interior trim
- Permit fees (typically $3,000β$8,000 for a structure this size)
- Architect or engineer stamping fees ($1,500β$5,000)
- Contingency reserve β add 15β20% to your base estimate for unexpected costs
Step 4: Hire a Local Architect or Engineer to Stamp the Plans
Most jurisdictions require drawings to be signed and stamped by a licensed architect or engineer registered in your state before the building department will accept them for review. With a permit-ready plan set, this professional's role is primarily to review the plans, confirm they meet your local code requirements, and certify them β rather than designing from scratch.
Get quotes from two or three local firms. Make clear you are starting with a complete, engineered plan set rather than asking for original design work. This distinction significantly reduces their fee compared to custom design work.
Step 5: Submit Your Permit Application
Your building department will require stamped architectural drawings (floor plans, elevations, foundation plan, electrical, plumbing, and mechanical), a site plan showing the structure's placement relative to all property lines, energy compliance documentation, and payment of permit fees. Submission can typically be done in person, by mail, or through an online portal depending on your jurisdiction.
Plan review turnaround varies widely β some building departments complete review in two to three weeks; others take three to six months. Ask your department for a current estimate when you submit.
Step 6: Build with Required Inspections
Once your permit is issued, construction can begin. Your permit will specify required inspections at key construction milestones before work is covered. Standard inspection points for a structure like this include:
- Foundation and footing inspection before concrete is placed
- Rough framing inspection before insulation and sheathing
- Rough electrical, plumbing, and HVAC inspections
- Insulation inspection
- Final inspection when all systems are complete and functional
Never cover work before it has been inspected. Failing to get a required inspection can require opening up completed walls to allow the inspector access, adding significant cost and time to the project.
Step 7: Final Inspection and Certificate of Occupancy
After passing all required inspections, your building department issues a Certificate of Occupancy (CO), which legally authorizes use of the structure as a livable space. Do not allow tenants to occupy the apartment before the CO is in hand β doing so creates legal and insurance liability regardless of how finished the space appears.
Keep your permit, approved drawings, and all inspection records permanently. These documents are required at resale and are sometimes requested by insurance carriers.
