How Much Does It Cost to Convert a Garage Into an ADU in California?

What Makes a Garage-to-ADU Conversion Different?

Not every garage conversion is an ADU project. Converting a garage into a bedroom, home office, or gym is relatively straightforward. You insulate, drywall, add flooring, and upgrade the electrical. No plumbing, no kitchen, no separate utility connections.

A garage-to-ADU conversion is a fundamentally different scope of work. You are building a fully independent living unit inside your existing garage shell. That means a complete kitchen, a full bathroom, a dedicated HVAC system, an electrical subpanel, separate plumbing lines, and a private entrance. These additions are what push garage-to-ADU costs well above a standard conversion.

In California, ADU conversions also fall under specific state regulations (AB 68, SB 13, AB 881) that dictate size limits, kitchen requirements, bathroom standards, and permitting timelines. Understanding these requirements is essential before you set a budget.

For a broader look at all types of garage conversion costs across the state, see our California garage conversion cost guide.

Full ADU vs JADU: Two Paths, Two Price Points

California law recognizes two types of units you can create from a garage conversion: a full Accessory Dwelling Unit (ADU) and a Junior Accessory Dwelling Unit (JADU). The cost difference between them is substantial.

Full ADU Conversion

A full ADU is a completely independent living unit with its own kitchen, bathroom, entrance, and utility connections. It can be up to 1,200 square feet (though most garage conversions max out at 400 to 600 square feet). Full ADUs do not require owner-occupancy, meaning you can rent out both the primary home and the ADU.

Cost range: $75,000 to $200,000+

JADU Conversion

A Junior ADU is carved from existing space within the primary home or an attached garage. JADUs are capped at 500 square feet, require only an efficiency kitchen (small sink, 120V appliances, no gas hookup), and may share a bathroom with the main house. If the JADU has its own bathroom, owner-occupancy is no longer required as of 2026.

Cost range: $50,000 to $150,000

Side-by-Side Comparison

Factor	Full ADU	JADU
Cost Range	$75,000-$200,000+	$50,000-$150,000
Max Size	1,200 sqft	500 sqft
Kitchen	Full kitchen required	Efficiency kitchen only
Bathroom	Dedicated, separate	Can share with main home
Utility Connections	Independent plumbing, electrical, HVAC	Can share with main home
Owner-Occupancy	Not required	Required (unless JADU has own bathroom)
Rental Income (Bay Area)	$1,800-$4,000/mo	$1,200-$2,200/mo
Timeline	4-8 months	3-5 months

The biggest factor driving the cost difference is utility separation. A full ADU needs its own plumbing supply and drain lines, water heater, electrical subpanel, and HVAC system. A JADU can tap into the existing home’s systems, saving $15,000 to $35,000 or more.

Cost Breakdown: Where Does the Money Go?

Understanding the component costs helps you make smarter decisions about where to invest and where to save. Here is how the budget typically breaks down for a full garage-to-ADU conversion in California.

Construction Costs ($50,000-$140,000)

Component	Cost Range	Notes
Garage door infill and framing	$5,000-$15,000	Replacing the garage door with a framed wall, window, or French doors; header modifications
Insulation and drywall	$4,000-$10,000	Walls, ceiling, vapor barrier to meet Title 24 energy standards
Electrical upgrade	$6,000-$18,000	New subpanel, circuits, outlets, lighting; possible meter separation
Plumbing	$8,000-$25,000	Kitchen and bathroom supply/drain lines, water heater, fixtures
HVAC	$4,000-$12,000	Mini-split heat pump is the most common; ducted systems cost more
Flooring	$3,000-$10,000	Slab leveling, moisture barrier, finished flooring (LVP, tile, or hardwood)
Kitchen buildout	$10,000-$30,000	Cabinetry, countertops, appliances, sink, range hood
Bathroom buildout	$8,000-$25,000	Tile, vanity, toilet, shower, ventilation fan
Windows and doors	$3,000-$10,000	Egress windows, separate entrance door, possible sliding glass door

Soft Costs ($15,000-$40,000)

Component	Cost Range	Notes
Design and architecture	$5,000-$15,000	Floor plans, construction drawings, Title 24 energy calculations
Permits and fees	$3,000-$15,000	Building permit, plan review, school impact fees, utility connection charges
Engineering	$2,000-$8,000	Structural engineering for load-bearing modifications, foundation assessment
Inspections	$500-$2,000	Required inspections during and after construction

Total Project Cost by Garage Size

Garage Type	Typical Sqft	Full ADU Cost	JADU Cost
One-car garage	200-280 sqft	$70,000-$130,000	$50,000-$90,000
Two-car garage	400-500 sqft	$100,000-$200,000+	$60,000-$150,000
Three-car garage	600-750 sqft	$150,000-$250,000+	N/A (exceeds 500 sqft JADU cap)

What Drives Costs Up (and Down)

Several factors can push your project well above or below the averages.

Factors That Increase Cost

Slab condition and foundation work. Most garage slabs are thinner than residential slabs and lack moisture barriers. If your slab needs reinforcement, leveling, or a new moisture barrier, expect to add $5,000 to $15,000.

Distance from existing utilities. The farther your garage sits from the main home’s plumbing and electrical, the more expensive utility connections become. Running a new sewer lateral 40 feet costs significantly more than tying into an adjacent bathroom’s drain line. Utility connection costs can range from $5,000 to $20,000 depending on distance and complexity.

Ceiling height limitations. Standard garages have 8-foot ceilings. If yours is lower, you may need to lower the floor (excavate the slab) or raise the roof, both of which add $10,000 to $30,000.

Bay Area labor premiums. Bay Area projects run 25-50% above statewide averages. Higher labor rates, more expensive permits, and premium finish expectations all contribute. A conversion that costs $120,000 in Sacramento may cost $160,000 to $180,000 in San Jose or Palo Alto.

High-end finishes. Marble countertops, hardwood flooring, custom cabinetry, and premium appliances push per-square-foot costs from $200 toward $400+.

Factors That Reduce Cost

Attached garages. Shorter plumbing and electrical runs mean lower utility connection costs. Attached garages also share a wall with the main home, reducing insulation and framing work.

Existing plumbing proximity. If your garage shares a wall with a kitchen or bathroom in the main home, tying into existing supply and drain lines is far cheaper than running new lines across the property.

JADU instead of full ADU. Choosing a JADU saves $20,000 to $50,000+ by eliminating the need for a full kitchen, separate bathroom, and independent utility connections.

Standard ceiling height. If your garage already meets the 7.5-foot minimum (or better, 8 feet), you avoid costly slab or roof modifications.

Permits and Legal Requirements

California’s ADU laws have streamlined the permitting process, but there are still important requirements to understand.

Permit Timeline and Fees

Under state law (AB 68), cities must review and approve compliant ADU applications within 60 days. In practice, the full timeline from plan preparation through permit issuance runs 6 to 12 weeks. Permit fees range from $3,000 to $15,000 depending on your jurisdiction, with Bay Area cities generally at the higher end.

No Parking Replacement Required

One of the biggest benefits of California’s ADU laws: you do not need to replace the parking spaces lost by converting your garage. This applies statewide to both attached and detached garage conversions.

Key Code Requirements

Your garage-to-ADU conversion must meet several building code standards.

• Title 24 energy compliance. Insulation, windows, and HVAC must meet California’s energy efficiency standards. This is one of the reasons insulation costs are higher than a basic garage remodel.
• Egress windows. Bedrooms require emergency escape windows meeting specific size requirements.
• Smoke and carbon monoxide detectors. Required in all habitable spaces.
• Separate entrance. ADUs must have their own entrance, separate from the primary home.
• Fire separation. Depending on proximity to property lines and the main home, fire-rated assemblies may be required.

What You Cannot Do

Some garage-to-ADU limitations are important to know upfront. JADUs cannot exceed 500 square feet. ADU conversions cannot exceed 1,200 square feet (though garage footprints rarely approach this limit). Short-term rentals (under 30 days) are prohibited for all ADUs and JADUs under state law.

Utility Connections: The Hidden Cost Driver

Utility connections are the single biggest factor separating a garage-to-ADU conversion from a standard garage remodel. They also represent the area where costs are hardest to estimate without a site assessment.

Plumbing ($8,000-$25,000)

A full ADU needs hot and cold water supply lines, drain/waste/vent lines, a water heater, and connections for the kitchen sink, bathroom fixtures, and possibly a washing machine. If your garage is far from the main sewer line, the drain connection alone can cost $5,000 to $10,000.

Electrical ($6,000-$18,000)

Most garages have a single circuit. An ADU needs a dedicated subpanel (typically 60-100 amps), multiple circuits for kitchen appliances, bathroom ventilation, HVAC, lighting, and general outlets. Some utility companies require a separate meter for ADUs, adding $2,000 to $5,000.

HVAC ($4,000-$12,000)

Mini-split heat pump systems are the most popular choice for garage ADU conversions. They provide heating and cooling without ductwork, install quickly, and meet Title 24 energy requirements. A single-zone mini-split runs $4,000 to $8,000 installed. Multi-zone systems or ducted options cost $8,000 to $12,000+.

Gas ($1,500-$5,000)

If your ADU kitchen includes a gas range or your water heater runs on gas, you need a gas line extension. Some homeowners avoid this cost entirely by choosing all-electric appliances and a heat pump water heater, which also simplifies Title 24 compliance.

Bay Area Cost Premium

Bay Area homeowners should plan for costs 25-50% above statewide averages. Several factors drive this premium.

Labor rates. Skilled tradespeople in the Bay Area command $75 to $150+ per hour, compared to $50 to $90 in other California markets. Labor accounts for 40-60% of the total project cost.

Permit fees. Bay Area jurisdictions charge $5,000 to $20,000 in permit and impact fees, compared to $3,000 to $10,000 in most other California cities.

Finish expectations. Bay Area homeowners and renters expect higher-quality finishes. Budget countertops, basic fixtures, and builder-grade flooring are less common in this market, which pushes material costs up.

Lot challenges. Hillside lots, narrow setbacks, and older homes with outdated electrical and plumbing systems all add complexity and cost.

For Bay Area-specific pricing, see our ADU cost guide for the Bay Area.

How a Garage-to-ADU Conversion Compares to Other Options

If you are evaluating your ADU options, here is how a garage conversion stacks up against the alternatives.

Option	Cost Range	Timeline	Key Advantage
Garage-to-ADU Conversion	$75,000-$200,000+	4-8 months	Lowest cost; existing structure reduces scope
Detached ADU (New Build)	$250,000-$500,000+	8-14 months	Full design freedom; higher rental income
Above-Garage ADU	$200,000-$400,000+	8-12 months	Preserves parking; adds second story
JADU (Within Home)	$50,000-$150,000	3-5 months	Most affordable; minimal disruption

For a detailed comparison of garage conversions versus detached ADUs, see our garage conversion vs detached ADU guide.

What to Expect: The Conversion Process

A garage-to-ADU conversion follows a predictable sequence. Knowing the steps helps you plan your timeline and budget.

1. Site assessment and feasibility. A contractor evaluates your garage’s structural condition, slab thickness, ceiling height, utility proximity, and local code requirements. This step identifies deal-breakers early.

2. Design and planning. An architect or designer creates floor plans, elevations, and construction documents. Title 24 energy calculations and structural engineering are completed during this phase.

3. Permitting. Plans are submitted to your local building department. Under California law, compliant ADU applications must be approved within 60 days. Expect 6 to 12 weeks total for plan preparation and permit issuance.

4. Construction. The typical sequence: demolition and prep, structural framing, rough plumbing, rough electrical, insulation, drywall, flooring, kitchen and bathroom installation, finish work, and final inspections. Construction takes 10 to 16 weeks for a full ADU.

5. Final inspections and certificate of occupancy. The building department inspects the completed unit. Once approved, you receive a certificate of occupancy that allows legal rental.

Get a Fixed-Price Estimate From Custom Home

At Custom Home, we use a two-phase design-build process for garage-to-ADU conversions. During Phase 1 (Design), we complete your site assessment, architectural plans, engineering, and permitting. At the end of Phase 1, you receive a detailed, fixed-price construction bid. No surprises, no budget creep.

Phase 2 (Build) only begins after you approve the final scope and price. This structure protects you from the cost overruns that are common in ADU projects, especially when utility connections reveal unexpected conditions behind the walls.

Ready to find out what your garage-to-ADU conversion will cost? Contact Custom Home for a free consultation and get a clear answer before committing to anything.