How much an ADU or garage conversion costs, from basic conversion to detached unit

What does a garage-to-ADU conversion cost?

Angi's 2026 guide reports an average of $110,000 for converting a garage into an ADU, with a range of roughly $150 to $400 per square foot. At the low end, Angi's figures for a basic attached single-car conversion without a full kitchen start in the tens of thousands. At the high end are two-car conversions with full kitchens, new windows and doors, raised floors and extensive utility work.

Angi also notes that converting a detached garage typically adds 20 to 30 percent over an attached one, mainly because of utility runs. The garage's condition matters as much as its location: a sound slab, straight walls and a roof in good shape keep costs down, while a cracked slab, rot or a failing roof push the conversion toward the cost of new construction.

What does a new detached ADU cost?

Zonda's 2025 Cost vs. Value report prices a 660 square foot detached ADU at $166,406, or about $252 per square foot, and found it recoups about 41 percent of that cost at resale before counting any rental income. That figure is a national average for a specified unit with a kitchen, bathroom and living space.

Local costs vary widely, driven by labor rates, site conditions, utility distances and local fees. A detached unit on a flat lot close to the house's utilities costs far less to build than one on a slope at the back of a deep lot. Prefabricated units can reduce construction time, but foundation, utilities, delivery and permits still apply. Setback and separation rules also affect cost, since a unit squeezed into a tight corner may need fire-rated walls or smaller windows facing the lot line.

How do kitchens, bathrooms and finish tiers change the total?

Kitchens and bathrooms are where most of the interior budget goes. A kitchenette with a small range, sink and compact refrigerator costs much less than a full kitchen with a range hood, dishwasher and more cabinetry. Some jurisdictions require a full kitchen for a unit to count as an ADU, so check the definition before scaling back. The bathroom earns its cost twice, since our analysis of EIA's 2024 survey found 38.6% of main houses have one full bathroom and only 30.3% have a half bath.

Finish tiers work as with other additions: basic finishes use stock cabinets, laminate counters and vinyl plank flooring; mid-grade adds better cabinets and tile; premium adds custom work and designer fixtures. For rental units, durable mid-grade finishes usually make the most sense, since they hold up to tenant use and appeal to a wide range of renters. For a parent or relative, spend instead on accessibility: a curbless shower, wider doors, lever handles and good lighting.

What do utilities, fees and site work add?

For detached units, utility connections are often the largest cost beyond the building. Trenching for water, sewer and power, and sometimes gas, can be substantial when the unit is far from the main house or the sewer line is shallow. A sewer that cannot drain by gravity needs a pump. The main electrical service may need an upgrade to carry the unit's load. ADU Wizard's 2026 guide lists sewer connection or upsizing at $5,000 to $30,000 or more, an electrical service upgrade at $3,000 to $15,000 or more, and trenching and utility runs at $5,000 to $25,000 or more.

• Utility trenching and connections for water, sewer, power and gas.
• Electrical service upgrade or a separate meter where required.
• Impact, connection or school fees, which some states limit for small units.
• Site work: grading, drainage, access paths and tree protection.
• Fire separation or sprinklers where local codes require them.
• Design, engineering and permit drawings, with plan review fees.

How much of an ADU budget is labor?

ADU budgets are usually split by phase rather than into labor and materials. ADU Wizard's 2026 cost breakdown for a typical 750 square foot detached unit, built on a roughly $300,000 project in what it calls a medium-cost area, is shown in the table in this section. Structure and mechanical systems take about half; site work and utilities alone can take a fifth. A garage conversion reuses the shell, so its budget shifts toward skilled trades: plumbing, electrical, insulation, drywall and finishes.

Because ADUs pack many trades into a small space, scheduling efficiency matters. Each trade may spend only a few days on site, and gaps between them add time and overhead. Builders with ADU experience sequence the work tightly. Ask bidders how many units they have completed and how long their typical conversion or new unit took after permit issuance. Their answers, checked against a reference or two, are a better predictor of your final cost than the headline price.

How does the schedule affect ADU costs?

Garage conversions usually take a few months after permits; detached units take longer because of foundations, full framing, utility trenching and more inspections. Permit timing depends on the jurisdiction. In states with ADU laws, cities may be required to approve compliant applications within a set time, which reduces uncertainty. California's Department of Housing and Community Development reports 26,924 ADUs permitted in 2023.

If the unit will be rented, every month of delay is lost income, which gives a real value to a faster schedule; FHFA data show California properties with an ADU appraised at a median $1,064,000 in 2023. For family use, the value depends on when the space is needed. In both cases, making selections before the start and choosing a builder with ADU experience are the most reliable ways to keep the schedule and its costs under control.

What should you cut first on an ADU budget?

Start with the size, since a smaller unit saves on every building element, and with the kitchen, which can be scaled back if local rules allow. Use standard windows, stock cabinets and durable mid-grade finishes. For conversions, keeping the existing slab and roof where they are sound saves significantly. For detached units, siting close to existing utilities reduces trenching, and a simple rectangular plan with one roof plane keeps framing and roofing costs down.

Do not cut fire separation, insulation, moisture protection at an old garage slab or a properly sized heating and cooling system. Those determine whether the unit is legal, comfortable and durable. If the budget is still short, compare the costs of the two routes on the ADU and garage conversion page before scaling back further.

What do sample ADU budgets look like?

A basic attached single-car conversion with a kitchenette may land near the low end of Angi's figures. A two-car conversion with a full kitchen and bathroom will usually be closer to Angi's $110,000 average. A 660 square foot detached unit at Zonda's national average is $166,406, and local conditions can move that in either direction.

Add design, engineering and permits, utility work, local fees and a contingency of ten to fifteen percent, more for older garages; Angi puts the average garage-to-ADU conversion at $110,000, so those extras are a large share. If you plan to rent, check local rents and any restrictions on rental terms, and remember that insurance and property taxes will rise with the new unit. For local prices, send a brief with the garage's condition and the unit's intended use through the estimate request form, or read the permits guide for the approval path.