How Much Does an ADU Cost in California? (2026 Guide)

ADU cost in California ranges from $60,000 for a basic JADU to $450,000+ for a large detached unit in a coastal market. The average cost for a 500 sq ft detached ADU in California is $200,000 to $300,000 including permits, site work, and standard finishes. But that statewide average hides enormous variation — a garage conversion in Sacramento costs half what the same project costs on a hillside lot in Los Angeles. This guide breaks down what California homeowners are actually paying in 2026 by ADU type, by region, and by cost category.

Every number in this guide comes from market data across the three regions where VerifiedADU operates: Sacramento, Los Angeles, and San Diego. For city-specific breakdowns, follow those links. This page is the statewide overview.

ADU Type	Size Range	Statewide Cost Range	Cost Per Sq Ft
Garage Conversion	200–500 sq ft	$80,000 – $180,000	$250 – $450
JADU	150–500 sq ft	$60,000 – $150,000	$200 – $400
Attached ADU	400–1,200 sq ft	$150,000 – $400,000	$300 – $500
Detached ADU	400–1,200 sq ft	$180,000 – $450,000	$350 – $550
Prefab / Modular	400–1,200 sq ft	$120,000 – $300,000	$250 – $420

These ranges include permitting, site preparation, construction, and standard finishes. They do not include furniture, landscaping, solar panels, or luxury upgrades.

Garage Conversion — $80,000 to $180,000

Garage conversions are the most affordable ADU option because the structure already exists. You’re converting enclosed space, not building from scratch. The cost depends on the garage’s condition, age, and how much plumbing and electrical work is needed. Under current California law, no replacement parking is required when converting a garage to an ADU.

Garage conversions are also the fastest ADU type to build — 3 to 5 months of construction versus 5 to 10 months for a detached unit. For a complete breakdown, see our garage conversion guide.

JADU (Junior ADU) — $60,000 to $150,000

A JADU converts existing space within the primary home — a bedroom, bonus room, or attached garage — into a separate dwelling unit. JADUs are capped at 500 sq ft and require a cooking facility (which can be as simple as a sink, countertop, and small appliance). JADUs are the cheapest option because you’re working within existing walls. Owner-occupancy may be required.

Attached ADU — $150,000 to $400,000

An attached ADU adds new construction to the existing home. These projects involve new foundation work or structural reinforcement, utility tie-ins, and exterior matching. Second-story ADUs over garages are increasingly common in urban markets where lot depth is limited.

Detached ADU — $180,000 to $450,000

A standalone structure in the backyard. Most expensive but most versatile — functions as a completely independent living space. California allows detached ADUs up to 1,200 sq ft on most single-family lots. The wide cost range reflects enormous variation in site conditions across the state.

Prefab / Modular ADU — $120,000 to $300,000

Factory-built modules delivered to the site and placed on a prepared foundation. Faster construction (2 to 4 months after delivery) but total installed cost is often close to conventional construction because site work, foundation, utility connections, and permitting costs are the same.

Location is the single biggest cost variable. The same 600 sq ft detached ADU costs 40% more in LA than in Sacramento.

ADU Type	Sacramento	Los Angeles	San Diego
Garage Conversion	$80K – $150K	$100K – $180K	$90K – $160K
JADU	$50K – $120K	$70K – $150K	$60K – $130K
Attached ADU	$150K – $300K	$200K – $400K	$170K – $330K
Detached ADU	$180K – $350K	$250K – $450K	$200K – $380K
Prefab / Modular	$120K – $250K	$150K – $300K	$130K – $260K

Why LA costs more: Higher labor rates ($45–$85/hr vs. $35–$65 in Sacramento), more complex permitting through LADBS, hillside lot complications, and higher material costs due to transportation and demand.

Why Sacramento is cheapest: Lower labor rates, faster permitting (4–8 weeks vs. 8–16 in LA), flat lots without hillside complications, and lower overall cost of business.

San Diego: Falls between Sacramento and LA — 10% to 20% cheaper than LA, 10% to 15% more than Sacramento. Faster permitting than LA and year-round construction climate.

For detailed breakdowns for each city: Sacramento Cost Guide · Los Angeles Cost Guide · San Diego Cost Guide

Fee Category	Statewide Range	Notes
Building permit	$1,000 – $5,000	Based on project valuation
Plan check	$650 – $3,500	Typically 65% of building permit fee
School fees	$1,500 – $6,000	$4.79/sq ft for new residential
Sewer connection	$2,000 – $8,000	Varies by jurisdiction and distance
Impact fees (>750 sq ft)	$0 – $4,000	Waived for ADUs under 750 sq ft
Total permit costs	$3,000 – $15,000	Lowest in Sacramento, highest in LA

Fee waiver: California law waives most development impact fees for ADUs under 750 sq ft. Designing your ADU just under that threshold saves $2,000 to $4,000 in most jurisdictions.

For a step-by-step walkthrough of the permit process, see our ADU Permits California guide.

Soft costs are the professional services required before construction begins. Statewide, these add $10,000 to $35,000 to the total project cost.

Service	Cost Range
Architectural plans	$4,000 – $15,000
Structural engineering	$2,500 – $8,000
Title 24 energy calculations	$1,200 – $3,000
Soil / geotechnical report	$2,000 – $8,000
Site survey	$1,000 – $3,000
Feasibility / zoning review	$500 – $2,000

Design-build firms bundle these into the construction contract. If a contractor quotes a per-square-foot price, ask whether it includes or excludes design and engineering — the answer swings your total budget by $15,000 or more.

Cost Factor	Sacramento	Los Angeles	San Diego
Skilled labor (per hour)	$35 – $65	$45 – $85	$40 – $75
GC markup	12% – 20%	15% – 25%	15% – 22%
Materials vs. national avg	+5% – 8%	+10% – 15%	+8% – 12%
Concrete (per cubic yard)	$130 – $160	$150 – $190	$150 – $180

Labor typically accounts for 40% to 50% of total ADU construction cost. Materials account for 30% to 35%. The remaining 15% to 25% covers permits, soft costs, and contractor overhead.

These costs don’t appear in most online calculators or initial contractor quotes but show up on the final invoice:

• Sewer lateral replacement: $5,000 to $25,000. Many cities require inspection or replacement of the existing sewer lateral when adding an ADU. Older neighborhoods are most affected.
• Electrical panel upgrade: $3,000 to $6,000. Homes with 100-amp or 150-amp panels often need a 200-amp upgrade to support the ADU.
• Hillside grading and retaining walls: $15,000 to $40,000+. Common in LA hillside neighborhoods and parts of San Diego. Flat lots avoid this entirely.
• Fire zone requirements: $5,000 to $15,000. Properties in Very High Fire Hazard Severity Zones require fire-resistive construction, ember-resistant vents, and brush clearance.
• Coastal Commission review: $3,000 to $8,000 in fees plus 2 to 6 months added to timeline. Affects coastal San Diego and parts of LA.
• Tree removal: $1,000 to $8,000. Protected tree ordinances in LA and other cities require permits and mitigation plans.
• Utility trenching: $3,000 to $10,000. Running water, sewer, gas, and electrical from the house to a detached ADU at the back of the lot.

Rule of thumb: Budget 15% to 20% above the construction quote for contingency. If your contractor quotes $250,000, plan for $290,000 to $300,000 total.

The California Housing Finance Agency (CalHFA) offers a grant of up to $40,000 to help homeowners cover pre-development costs. This is a grant — no repayment required.

What the $40,000 covers: Architectural plans, engineering, permits, impact fees, soil tests, site surveys, and Title 24 energy calculations.

What it does not cover: Construction costs, materials, labor, landscaping, or furniture.

Eligibility: Owner-occupied property, CalHFA-approved lender required, income limits may apply, one grant per person. Available statewide — Sacramento, LA, San Diego, and every other California jurisdiction.

In markets where total soft costs run $10,000 to $30,000, the CalHFA grant can cover most or all of your pre-construction expenses. For a complete walkthrough, see our CalHFA ADU Grant guide.

ADU Size	Sacramento Rent	LA Rent	SD Rent
Studio (300 sq ft)	$1,100 – $1,400	$1,400 – $1,800	$1,300 – $1,700
1-bed (500 sq ft)	$1,400 – $1,800	$1,800 – $2,400	$1,700 – $2,200
2-bed (800 sq ft)	$1,800 – $2,300	$2,400 – $3,200	$2,200 – $2,800

A permitted ADU typically adds 20% to 35% to a property’s appraised value. In many California markets, the added property value exceeds the construction cost — making an ADU one of the highest-ROI home improvements available.

Payback period: Most California ADUs pay for themselves in 8 to 13 years through rental income alone. Sacramento has the shortest payback (lower construction cost, competitive rents). LA has the longest (highest construction cost, despite highest rents).

ADUs built after January 1, 2025 cannot be used as short-term rentals. Plan for long-term tenant income. For rental rules, see our ADU rental guide.

How much does an ADU cost in California?

ADU costs in California range from $60,000 for a basic JADU to $450,000+ for a large detached unit in a coastal market. The average 500 sq ft detached ADU costs $200,000 to $300,000 including permits, site work, and standard finishes. Sacramento is cheapest, LA is most expensive, San Diego falls between.

What is the cheapest ADU to build in California?

A JADU (junior ADU) is the cheapest at $60,000 to $150,000 because it converts existing space within the home. A garage conversion is next at $80,000 to $180,000. Both avoid new foundation and framing costs.

How much does a 500 sq ft ADU cost in California?

A 500 sq ft detached ADU costs approximately $175,000 to $250,000 in Sacramento, $225,000 to $300,000 in San Diego, and $250,000 to $350,000 in Los Angeles. A 500 sq ft garage conversion costs $100,000 to $160,000 statewide.

How much do ADU permits cost in California?

Total ADU permit costs range from $3,000 to $15,000 depending on city and ADU size. ADUs under 750 sq ft are exempt from most development impact fees. Sacramento and San Diego are generally cheaper ($3,000 to $12,000). LA runs higher ($4,000 to $15,000).

Is there a grant for building an ADU in California?

Yes. The CalHFA ADU Grant provides up to $40,000 for pre-development costs including architectural plans, engineering, permits, and surveys. It is a grant — no repayment required. The property must be owner-occupied and you must use a CalHFA-approved lender.

How much rental income can I earn from an ADU in California?

Monthly ADU rental income in California ranges from $1,100 to $1,400 for a studio in Sacramento, $1,400 to $1,800 in LA, and $1,300 to $1,700 in San Diego. One-bedroom ADUs rent for $1,400 to $2,400 depending on market. Annual income of $15,000 to $38,000 is typical.

Is it worth building an ADU in California?

For most California homeowners, yes. A permitted ADU adds 20% to 35% to property value and generates $15,000 to $38,000 per year in rental income. Payback period is typically 8 to 13 years. The strongest ROI is in Sacramento (lowest construction costs) and LA (highest rents).

What is the most expensive part of building an ADU?

Construction labor is the largest single cost component at 40% to 50% of total project cost. Foundation work is the most expensive individual construction phase for detached ADUs. For garage conversions, plumbing installation (kitchen and bathroom) is typically the most expensive line item.