Garage ADU

Increase living space on the property you already own, perfectly suited to your needs.

Do you have a garage that is not used as vehicle space? Has it been on your To Do List forever to declutter? Have you been thinking about converting it into a living space? We are here to make it possible!  

There are three types of garage conversion ADUs:

  1. Detached ADU garage conversion through remodel
  2. Detached ADU garage conversion through re-build
  3. Attached ADU garage conversion 

Let us walk you through the process of how to convert your structurally solid garage into a livable space, from start to finish when you do not have to re-build from scratch. 

Garage ADU Roadmap:

  1. Reality check: structure vs estimate
  2. Budget approval and financing
  3. Plan set and permit submittal
  4. City fees and getting building permit
  5. Signed contract with builder
  6. Foundation vapor barrier and the first city inspection
  7. Framing stage: windows and doors
  8. Rough plumbing, electrical, mechanical (bathroom fans and HVAC)
  9. Adding Insulation and patching up drywall
  10. Installing bathroom and kitchen amenities
  11. Final inspection signed by the city building inspector

Cost to Convert Garage to ADU

The cost of converting a garage into an accessory dwelling unit varies depending on the size of the space, how many bedrooms and bathrooms there are, and whether the building has been recently built or renovated. The range for cost of conversion is from $80,000 to $250,000. These costs should include everything from demolition to construction costs. It should also take into account the square footage of the space, number of rooms, and any renovations needed.

Garage conversion permit cost

The initial visit of our general contractor or ADU specialist will determine if the existing structure needs professional evaluation by a structural engineer. Garage conversion permits require floor plans, elevations, sections, foundation and framing plans for the structure as built and what it will become after the construction process. It will have to demonstrate that it is built to current local building codes.

CalGreen requirements will need to be met. It will have to be all electric with the heat pump water heater and induction cooktop.

planset with ADU floor plan

What should a Garage ADU permit set include?

Surprisingly, the same information that any new construction plan set requires. Here are the main 8 blocks.

Title Sheet

ADU floor plan

Roof Plan

Foundation Plan


Building Sections

Structural information

Energy efficiency report

ADU Garage Conversion Cost

If you are using the old garage structure, you save money by remodeling instead of building from scratch. This is why garage ADU is often the best option to add extra square feet. But you have to prove to the building inspector that the building is safe for people.

If a general contractor or a structural engineer tell you the building needs new foundation, studs and beams, this makes a project a detached accessory dwelling unit construction.

The success of your garage ADU project today depends on reliable ADU contractors. Make sure whoever you select has proven experience doing work that will need to be done to pass inspections.

What can drive up the cost of converting existing garage to ADU?

  1. Garage floor and concrete slab issues
  2. Changing garage door opening to French Doors
  3. Adding natural light with skylights
  4. Need for new electrical wire or panel upgrade
  5. Existing sewer line or septic tank
  6. Amount of trenching for sewer and water lines
  7. Need to add fire rated features or address fire truck access issues

It is often old detached garages that require demolition and new construction. Attached garages were generally built the same way as the main house and can be converted to attached accessory dwelling unit or junior ADU more easily.

detached adu garage conversion

It’s not uncommon for people to underestimate how much it costs to convert garage space. In fact, according to the California Housing Finance Agency, the average cost to permit an ADU is $40,000. They have issued a special grant to cover these pre-construction costs for homeowners with low and moderate income. That means that even if you’re able to afford predevelopment costs ( those include site prep, architectural designs, permits, soil tests, impact fees, property survey, and energy reports), you might still need to borrow more to complete the project. With current interest rates, we can only hope that you have already established a home equity line of credit.

The cost of building a garage varies depending on where you live, how much space you have, what type of construction you want, etc.

Is a garage conversion worth it?

Does garage conversion add value? This depends on your neighborhood. Do people who live around you value their garage space as vehicle space? Or is housing a more pressing issue? If an appraiser comes to evaluate your property, he or she will add the value of the converted space but also subtract the value that was previously attributed to a garage. Consider your priorities carefully, discuss with financial advisor if needed.

Three possible scenarios*

How much to convert garage into ADU

Turning your garage into a living space can be a great way to add additional square footage to your home. However, there are a few things you need to keep in mind before starting any construction. First, check with your city or county to see if there are any zoning regulations that would prohibit you from converting your garage into living quarters. Second, consult with a contractor to see if your garage is structurally sound enough to support the additional weight of drywall, insulation, and flooring. Finally, make sure you have the necessary permits before beginning any work.


Scenario #1

  • Structurally safe building
  • Garage has windows
  • Existing water and sewer line 

Major Remodel

Scenario #2

  • Structure needs reinforcement
  • New egress windows 
  • Repairs to exterior 

Build New

Scenario #3

  • Tear down and rebuild
  • New foundation
  • New building envelope 

* Your estimate may differ – depending on the state of foundation, building envelope, electrical panel and other existing utilities.
Garage conversion ADU sounds like a challenge?

We make it easy to get started


Create property site plan

Let us answer three questions together: 1. How much space can you use for living quarters? 2. How safe is the structure if used for living? 3. How much can you afford to spend on construction?


Select the best Garage ADU floor plan

We do not like to invent wheels or bicycles. Let us get started with the plan that fits most of your requirements and then tweak it to make your garage shine as an accessory dwelling unit.


Assign the team

The success of a construction project hinges on how well the team communicates. You have a contractor you like? Bring her or him on board. We are happy to support you with the design, engineering and construction – when needed.


Gather Necessary Documents

Let us start with the best information available. What do you already have? Title report. Floor plan or site plan of your main house. Survey. Soil report. All these documents are a great foundation for your future successful construction project. Pun intended.


Compile the permit plan set

The number of pages in your plan set can differ from 8 to 30. It all depends on property specifics and city (or county) requirements. The better prepared your first submission is, the faster you get your permits. 


Respond to Plan Checker comments

Do you know that the most frequent reason it takes such a long time to pull permits is the number of weeks that passed between the day the city had given plan check comments and the day your team responded to them?

Case study: old metal garage structure makes space for new ADU

2 Bedroom Prefab ADU replaces an old detached garage


Demolish an old garage structure, install a modular unit on concrete perimeter foundation. Add deck and parking spot. Add separate meter for ADU. Keep the tree.

  • Ramp for carts and prams
  • Two bedrooms
  • Deck facing the backyard and main house
  • Matching the color of main house


Electrical Panel upgrade needed.

Connect to existing sewer line.

The local jurisdiction at the time did not assign addresses to ADUs.

PG&E allows separate meters only with a separate address.

Small 570 sf ADU
Completed in September 2021


The permitting process started in January 2021. Resubmitted in March 2021. Permit received May 2021.

The construction started May 2021. Foundation poured June 2021. The panel upgrade was done in July 2021. The unit arrived August 2021. Final inspection was passed September 2021.

The contractor was not able to add a separate meter for ADU because of conflicting requirements of the City and PG&E.

Total cost of project $235,000.

The tree survived construction.

From 300 Sq Ft to 600 Sq Ft - see what fits in each floor plan size

Three Popular Garage ADU Floor Plans

one car garage ADU
one car garage

Garage ADU Floor Plan 300 sq ft

This super narrow former garage space with attached workshop  is converted into a small one bedroom unit with a galley kitchen space, small living room and a bathroom with a shower.  

24x24 garage adu
two car garage

Garage ADU Floor Plan 500 sq ft

This one bedroom one bathroom ADU design has a comfortable living area, a bedroom with a closet, laundry space and the bathroom with the tub. 

garage adu
two car garage

ADU Floor Plan 600 sq ft

This spacious garage ADU has a full bathroom with a full size tub and a dedicated laundry space.  There is room for a full size kitchen area,  space for an island and sofa with TV area.

Whichever ADU floor plan you select, you will not pass a final inspection without these features

Essentials for any of Garage ADU floor plans


Type of insulation is called out in your Title 24 report provided by your energy consultant or HERS rater.

Kitchen Appliances

All ADU floor plans should show sink, cooktop, hood and fridge. These items are essential for anyone living permanently in the ADU.

Fire and CO2 Alarm

Smoke and carbon monoxide alarms are required on the wall or ceiling outside of each sleeping area. 

HVAC and Ventilation

Ductless mini splits are an accepted way to heat and cool your ADU. Energy Recovery Ventilators are an energy-efficient way to maintain indoor air quality.

Water Heater (Heat Pump)

As California goes all electric, think about the sizing of your pump – it depends on the number of people living in the ADU.

Address Numbers

ADUs are often required to have two sets of a minimum of 4 inch high house numbers – with one on ADU and an extra that is seen from the public road.