How Much Does It Cost to Convert a Garage to an ADU? [2025 Data]

Garage Living Space vs. Conversion to an ADU

Converting a garage into an ADU requires more planning, permitting, and money than simply turning a garage into additional living space, such as a bedroom or entertainment room. An ADU is an independent living space that must contain its own kitchen, bathroom, and other features, many of which depend on regulations in your area. 

Be prepared for a larger price tag, closer to the cost of building an in-law suite, and more stringent construction rules from your municipality.

Size of Garage Conversion to an ADU

Garage size is a major factor when converting a garage to an ADU. Converting a two-car garage will cost less than converting a three-car garage. However, calculating the cost difference between large and small isn't linear due to the need for infrastructure like sewer, plumbing, HVAC, and electricity, which aren’t dictated simply by the size of the space.

In some jurisdictions, a one-car garage doesn't have enough floor space to qualify for ADU conversion unless you add a second story. Here’s a look at the average price of garage ADUs based on common garage sizes.

Materials

The cost of materials when converting a garage to an ADU is highly variable. Often, materials make up between 40% and 50% of the project's cost. However, if the existing garage is in excellent condition, material costs land on the low end of that range. 

Architect and Designer Costs

Because of its small size, converting a garage to an ADU requires an excellent design plan to create a functional and comfortable home space. Two professionals—a designer and an architect—should be considered during the planning stages of your ADU.

The cost to hire an architect depends on their experience and the project size. For a garage conversion, expect a price between $2,000 and $6,600 for a set of plans. You'll likely need to obtain a building permit and outline the project for the various tradespeople who'll build the ADU. 

In addition to hiring an architect, you may want to hire an interior designer to help ensure the dwelling unit lives up to its potential. Interior designer prices range from $50 to $200 per hour. 

Structural Engineer Cost

Your municipality will likely require you to get a building permit for ADU construction or any garage conversion. Because garages aren't intended as living spaces, turning one into a home can require significant structural changes. 

Many municipalities will accept basic plan drawings when you apply for a permit. However, some will require a structural engineer to sign off on the plans before issuing a permit. The cost to hire a structural engineer ranges between $70 and $250 per hour.

Carpenter Cost 

When converting a garage to an ADU, your carpenter will likely be one of the first tradespersons necessary. Garage conversion requires building a wall where the garage door exists and installing windows and doors. The average cost of carpentry is between $75 and $100 per hour. However, the cost of installing cabinetry or other specialty items can vary from that norm, and each task may have a different associated cost. 

HVAC Installer Cost

An ADU will need its own heating and cooling system to be legal in most locations. Installing a cost-effective and efficient system, such as a heat pump, costs between $3,900 and $5,900. 

Plumber Costs

Your plumber will be crucial to the project's success from the start. Converting a garage to an ADU requires sewer, supply lines, rough-in, and finish plumbing.

• Sewer line installation: $1,435–$5,735

• Rough-in plumbing for a bathroom and kitchen: $1,600–$2,900 each

• Installing a sink: $220–$645

• Shower installation: $500–$3,000

• Toilet installation: $225–$533

• Faucet installation: $160–$365 each

Electrician Costs 

You’ll save some money if electricity already exists in the garage. However, an electrician will need to add additional circuits and ensure the ADU electrical meets code requirements for a living space. Like the plumber, the electrician must perform rough-in work and then return to complete the installation.

• Running electricity to a detached garage: $1,000–$3,000

• Outlet installation: $130–$300 each

• Installing a light fixture: $155–$955 each

• Installing a dedicated circuit: $570–$1,000

Insulation Installation Cost

Depending on the climate where you live, municipal regulations, and how energy efficient you'd like to make your ADU, the cost to install insulation in the walls and ceiling or roof will be between $1,065 and $2,600 or more for a typical two-car-sized garage conversion. Your conversion may require more than one type of insulation, depending on climate and its configuration.

Drywall Installer Cost

After the HVAC, plumbing, and electrical rough-in work is complete, your ADU will need wall covering. The most common wall covering is drywall. The cost of professional drywall installation, including labor and materials, runs between $1.50 and $3 per square foot.

Wall Finisher Costs

A little paint goes a long way in putting the finishing touches on the new living space. While you can also choose finishes like wallpaper, tile, or paneling, your ADU will likely require at least some paint. 

• Painting cost: $2.75–$4.70 per square foot

• Wallpapering cost: $315–$820

• Tile installation cost: $5–$45 per square foot

• Paneling installation cost: $1–$40 per square foot

Flooring Installation Cost