In This Guide
Building an ADU (Accessory Dwelling Unit) in San Diego is one of the smartest investments you can make. With California's ADU-friendly laws and San Diego's high rental demand, an ADU can generate $1,500-$3,500/month in rental income while adding significant value to your property.
This comprehensive guide covers everything you need to know about ADU costs, permits, and ROI in San Diego County.
What is an ADU?
An ADU (Accessory Dwelling Unit) is a secondary living unit on a residential property. Also called:
- Granny flat
- In-law suite
- Backyard cottage
- Casita
- Secondary unit
California state law (AB 881, SB 13) requires cities to allow ADUs on most residential properties. San Diego has streamlined the process with pre-approved ADU plans and reduced fees.
ADU Costs by Type
| ADU Type | Size Range | Cost Range | Cost/Sq Ft |
|---|---|---|---|
| Garage Conversion | 400-600 sq ft | $80,000 - $150,000 | $150-$250 |
| Detached (New Build) | 400-1,200 sq ft | $150,000 - $350,000 | $300-$450 |
| Attached ADU | 400-800 sq ft | $120,000 - $250,000 | $250-$375 |
| Interior Conversion | 300-600 sq ft | $60,000 - $120,000 | $150-$200 |
| Prefab/Modular ADU | 400-800 sq ft | $120,000 - $220,000 | $275-$350 |
San Diego Market Reality
ADU costs in San Diego run 15-25% higher than inland California due to labor costs, material prices, and stricter building standards. Budget at least $300/sq ft for a quality new-build ADU with permits and site work included.
Garage Conversion Costs (Most Popular)
Converting an existing garage to living space is the most cost-effective ADU option in San Diego. Here's what to expect:
Typical 2-Car Garage Conversion (400 sq ft)
| Category | Cost |
|---|---|
| Design & Permits | $5,000 - $12,000 |
| Foundation Work | $3,000 - $8,000 |
| Framing & Insulation | $8,000 - $15,000 |
| Electrical (panel, outlets, lighting) | $6,000 - $12,000 |
| Plumbing (kitchen + bath) | $10,000 - $20,000 |
| HVAC (mini-split) | $3,500 - $7,000 |
| Drywall & Paint | $5,000 - $10,000 |
| Flooring | $3,000 - $6,000 |
| Kitchen (cabinets, counters, appliances) | $12,000 - $25,000 |
| Bathroom (full bath) | $10,000 - $18,000 |
| Windows & Doors | $4,000 - $10,000 |
| Exterior (siding, stucco, finishes) | $5,000 - $12,000 |
| TOTAL | $75,000 - $155,000 |
New Construction ADU Costs
Building a new detached ADU offers more design flexibility but costs significantly more:
Detached ADU Cost Breakdown (600 sq ft)
| Category | Cost |
|---|---|
| Design & Engineering | $8,000 - $20,000 |
| Permits & Fees | $5,000 - $15,000 |
| Site Prep & Foundation | $25,000 - $45,000 |
| Framing | $25,000 - $40,000 |
| Roofing | $8,000 - $15,000 |
| Electrical | $10,000 - $18,000 |
| Plumbing | $12,000 - $25,000 |
| HVAC | $5,000 - $10,000 |
| Interior Finishes | $30,000 - $50,000 |
| Exterior Finishes | $15,000 - $30,000 |
| Utilities Connection | $8,000 - $20,000 |
| Landscaping | $3,000 - $10,000 |
| TOTAL | $154,000 - $298,000 |
San Diego ADU Permits & Fees
San Diego has streamlined the ADU permit process:
| Fee Type | Cost |
|---|---|
| Plan Check | $1,500 - $4,000 |
| Building Permit | $1,000 - $3,000 |
| School Fees | $3 - $5/sq ft |
| Utility Connection Fees | $2,000 - $8,000 |
| TOTAL PERMIT COSTS | $5,000 - $15,000 |
San Diego ADU Requirements
- Max Size: 1,200 sq ft (detached) or 50% of primary home (attached)
- Setbacks: 4 feet from side/rear property lines
- Height: Up to 16 feet (2-story ADUs allowed)
- Parking: Not required in most cases (within 1/2 mile of transit)
- Separate Entrance: Required
- Owner Occupancy: Not required (you can rent both units)
Rental Income & ROI
ADUs in San Diego generate strong rental returns:
| ADU Size | Monthly Rent | Annual Income |
|---|---|---|
| Studio (300-400 sq ft) | $1,500 - $2,000 | $18,000 - $24,000 |
| 1BR (400-600 sq ft) | $2,000 - $2,800 | $24,000 - $33,600 |
| 2BR (700-1,000 sq ft) | $2,800 - $3,500 | $33,600 - $42,000 |
Sample ROI Calculation
Garage Conversion Example
Investment: $120,000 (400 sq ft garage conversion)
Monthly Rent: $2,200
Annual Income: $26,400
Cash-on-Cash Return: 22%
Payback Period: 4.5 years
Property Value Increase: $150,000 - $250,000
ADU Project Timeline
| Phase | Duration |
|---|---|
| Design & Plans | 4-8 weeks |
| Permit Approval | 4-12 weeks |
| Garage Conversion | 8-16 weeks |
| New Construction ADU | 16-24 weeks |
| Final Inspections | 1-2 weeks |
| TOTAL (Garage) | 4-7 months |
| TOTAL (New Build) | 8-12 months |
Get Your ADU Cost Estimate
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