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Cost Estimates by ADU Type
| ADU Type | Low Estimate | Mid Estimate | High Estimate | Per Sq Ft |
|---|---|---|---|---|
| Detached ADU (800 sq ft) | $150,000 | $225,000 | $350,000 | $190-$440 |
| Attached ADU (600 sq ft) | $100,000 | $165,000 | $250,000 | $165-$415 |
| Garage Conversion (400 sq ft) | $60,000 | $110,000 | $180,000 | $150-$450 |
| Basement ADU (500 sq ft) | $50,000 | $90,000 | $150,000 | $100-$300 |
| JADU (400 sq ft) | $30,000 | $50,000 | $80,000 | $75-$200 |
| Prefab ADU (500 sq ft) | $80,000 | $150,000 | $250,000 | $160-$500 |
Cost Breakdown
Here is where your ADU budget typically goes:
| Category | % of Total | Typical Range |
|---|---|---|
| Construction / Labor | 50-60% | $75,000-$210,000 |
| Materials | 20-30% | $30,000-$105,000 |
| Design & Architecture | 8-12% | $8,000-$35,000 |
| Permits & Fees | 5-10% | $5,000-$30,000 |
| Utility Connections | 3-8% | $5,000-$25,000 |
| Contingency | 10-15% | $15,000-$50,000 |
Hidden Costs to Watch For
- Sewer/water connection fees (can be $5,000-$15,000+)
- School impact fees (waived under 750 sq ft in CA)
- Tree removal or site grading
- Upgraded electrical panel for main house
- Landscaping restoration after construction
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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Costs by City
Construction costs vary significantly by location. Here are average ADU build costs for popular California cities:
| City | Avg Build Cost | Cost/Sq Ft | Permit Fees |
|---|---|---|---|
| Los Angeles | $150,000-$350,000 | $200-$400 | $4,000-$15,000 depending on size and type (plus 10% General Plan Maintenance Surcharge on permit fees as of June 9, 2026) |
| San Francisco | $200,000-$450,000 | $300-$500 | $5,000-$20,000 depending on scope |
| San Diego | $120,000-$300,000 | $180-$350 | $3,500-$12,000 |
| San Jose | $180,000-$400,000 | $250-$450 | $4,000-$14,000 |
| Sacramento | $100,000-$250,000 | $150-$300 | $3,000-$10,000 |
| Oakland | $160,000-$380,000 | $250-$420 | $4,000-$15,000 |
| Long Beach | $120,000-$280,000 | $180-$330 | $3,000-$10,000 |
| Fresno | $80,000-$200,000 | $120-$250 | $2,500-$8,000 |
| Santa Ana | $130,000-$300,000 | $200-$360 | $3,500-$12,000 |
| Anaheim | $130,000-$290,000 | $195-$350 | $3,500-$12,000 |
Get an Accurate Quote
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