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How Much Does an ADU or Garage Conversion Cost?
Accessory Dwelling Units (ADUs), garage conversions, and room additions are among the most in-demand construction projects in California. Whether you're adding living space for family, creating a rental income property, or converting an underused garage - here's a comprehensive cost guide for Southern California.
Cost Breakdown by Project Type
| Project Type | Typical Cost Range | Timeline |
|---|---|---|
| Garage conversion (2-car garage) | $80,000 – $150,000 | 3–5 months |
| Attached ADU (400–800 sq ft) | $150,000 – $280,000 | 5–9 months |
| Detached ADU (400–1,200 sq ft) | $200,000 – $350,000+ | 6–12 months |
| Room addition (200–500 sq ft) | $80,000 – $200,000 | 3–6 months |
| Second story addition | $150,000 – $400,000+ | 4–8 months |
ADU Cost Breakdown (Detached, 600 sq ft)
| Component | Typical Cost |
|---|---|
| Foundation & site work | $15,000 – $30,000 |
| Framing & structural | $20,000 – $40,000 |
| Roofing | $5,000 – $15,000 |
| Plumbing (rough & finish) | $10,000 – $25,000 |
| Electrical | $8,000 – $18,000 |
| HVAC | $5,000 – $12,000 |
| Insulation & drywall | $8,000 – $15,000 |
| Kitchen & bathroom finishes | $15,000 – $35,000 |
| Flooring | $4,000 – $10,000 |
| Windows & doors | $5,000 – $12,000 |
| Design, permits & engineering | $10,000 – $25,000 |
California ADU Laws You Should Know
California has some of the most ADU-friendly laws in the country. Recent legislation has made it easier and more affordable than ever to add an ADU:
- Most single-family lots can add at least one ADU by right
- Many cities have reduced or waived impact fees for ADUs under 750 sq ft
- Parking requirements have been eliminated for ADUs near transit
- Owner-occupancy requirements have been relaxed in many jurisdictions
- ADUs up to 1,200 sq ft are generally permitted on most residential lots
RL Remodeling specializes in ADUs and garage conversions. Our team handles design, engineering, permitting, and construction. We navigate city requirements so you don't have to. Call (888) 324-1144 for a free consultation.
Frequently Asked Questions
How much does an ADU cost in California?
ADU costs in California typically range from $150,000 to $350,000+ depending on size, type (detached vs. garage conversion), finishes, and local requirements. A garage conversion is the most affordable option, starting around $80,000–$150,000.
How much does a garage conversion cost?
Converting a two-car garage into livable space typically costs $80,000–$150,000 in Southern California. This includes structural modifications, insulation, electrical, plumbing, flooring, drywall, windows, and finishes.
How much does a room addition cost?
Room additions in Southern California typically cost $200–$500+ per square foot, depending on the type of addition. A 400 sq ft room addition can cost $80,000–$200,000+ including foundation, framing, roofing, and all interior finishes.
What is the cost per square foot to build an ADU?
ADU construction in Southern California ranges from $250–$500+ per square foot. Garage conversions are on the lower end ($200–$350/sq ft) since the structure already exists. New detached ADUs are on the higher end ($350–$500+/sq ft).
Do ADUs add value to your home?
Yes. Studies show ADUs can increase property value by 20–30% in California. Additionally, ADUs generate rental income, with typical rents of $1,500–$3,000+/month in Southern California depending on location.
How long does it take to build an ADU?
From design to completion, an ADU typically takes 6–12 months. This includes 2–4 months for design and permitting, and 4–8 months for construction. Garage conversions are faster at 3–5 months total.
