ADU vs Room Addition: Which is Better for San Diego Homeowners?

Need more space? San Diego homeowners often debate between building an ADU or a room addition. Here's a detailed comparison to help you decide.

What's the Difference?

ADU (Accessory Dwelling Unit)

A separate, complete living unit with its own entrance, kitchen, bathroom, and living space. Can be detached or attached to the main home.

Room Addition

An expansion of your existing home—adding bedrooms, bathrooms, or living space that's integrated with the main structure.

Cost Comparison

ADU Costs

• Detached ADU: $300-$450/sq ft ($150,000-$350,000 for 500-800 sq ft)
• Garage Conversion: $150-$250/sq ft ($60,000-$150,000)
• Attached ADU: $250-$400/sq ft ($125,000-$300,000)

Room Addition Costs

• Basic bedroom: $200-$350/sq ft ($50,000-$100,000 for 200-300 sq ft)
• Bedroom + bathroom: $250-$400/sq ft ($75,000-$150,000)
• Second story: $300-$500/sq ft ($150,000-$400,000)

Income Potential

ADU: Significant Rental Income

ADUs can generate $2,000-$4,000/month in rental income in San Diego. This often pays for the construction loan within 5-7 years.

Room Addition: No Direct Income

Room additions add living space but don't generate rental income (unless used for house hacking).

Property Value Impact

ADU

• Adds 20-30% to property value
• Appeals to investors and multi-generational buyers
• Can be sold with income history showing rental potential

Room Addition

• Adds value proportional to added square footage
• Typically 50-70% ROI at resale
• Increases home's appeal to larger families

Permitting Complexity

ADU Permits

• California's ADU laws streamline approval
• Ministerial approval (must be approved if meets requirements)
• No parking required in most cases
• Relaxed setback requirements (4 ft from property lines)

Room Addition Permits

• Standard building permit process
• Must meet all zoning setbacks
• May require variance for non-conforming lots
• Design review in some neighborhoods

Timeline Comparison

ADU: 8-14 Months Total

• Design: 4-8 weeks
• Permitting: 4-12 weeks
• Construction: 4-6 months

Room Addition: 4-8 Months Total

• Design: 2-6 weeks
• Permitting: 4-8 weeks
• Construction: 2-4 months

Which Should You Choose?

Choose an ADU if you want to:

• Generate rental income
• House aging parents with privacy
• Create a home office separate from main home
• Maximize property investment value
• Eventually sell as a duplex investment

Choose a room addition if you want to:

• Add bedrooms for growing family
• Expand kitchen or living areas
• Add a master suite
• Keep one unified home
• Faster, potentially lower-cost option

Get Expert Advice

One Stop Builders builds both ADUs and room additions. We'll help you evaluate your property and goals to determine the best option. Call (858) 567-0007 for a free consultation.