Want to build an ADU but worried about the cost? While ADUs are a significant investment, there are ways to reduce costs without sacrificing quality. Here's your guide to the cheapest ADU options in San Diego.

Cheapest ADU Types Ranked

1. Garage Conversion ADU: $80,000-$150,000

The most affordable option because the structure already exists.

Uses existing walls, roof, and foundation
Shorter timeline (3-4 months)
Simpler permitting
Typical size: 400-600 sq ft

Key costs: New flooring, insulation, drywall, kitchen, bathroom, windows/doors, HVAC, electrical upgrade.

2. Junior ADU (JADU): $50,000-$100,000

Converting existing space within your home (max 500 sq ft).

Must be within existing home footprint
Requires efficiency kitchen (no full cooking requirement)
Can share bathroom with main home or have separate
Separate entrance required

Best for: Homes with underutilized space (large basement, unused wing).

3. Attached ADU: $125,000-$250,000

Building onto your existing home saves on some costs.

Shares one wall with main home
Less foundation and roofing needed
May tie into existing utilities more easily

4. Small Detached ADU: $150,000-$200,000

New construction but compact (400-600 sq ft).

Keep square footage modest
Simple, rectangular design
Standard materials and finishes

Cost-Saving Strategies

Design Smart

Simple footprint: Rectangles cost less than complex shapes
Standard sizes: 400, 600, or 800 sq ft optimize material usage
Single-story: No staircase or structural complexity
Use pre-approved plans: San Diego offers pre-approved ADU designs

Material Choices

Laminate vs. hardwood floors: Save $5,000-$10,000
Laminate vs. quartz counters: Save $2,000-$5,000
Stock cabinets vs. custom: Save $5,000-$15,000
Standard fixtures: Builder-grade saves vs. designer brands

Utility Connections

Locate ADU close to existing utilities to minimize runs
Consider shared sewer connection vs. separate
Evaluate if existing electrical panel has capacity

What NOT to Cheap Out On

Some things are worth paying for:

Foundation: Structural integrity is non-negotiable
Waterproofing: Especially in bathrooms and exterior
Electrical capacity: Must meet code and be safe
Insulation: Affects comfort and energy costs forever
Permits: Never skip—illegal ADUs have serious consequences

Budget ADU Rental Income

Even a budget ADU generates significant income:

400 sq ft studio: $1,500-$2,000/month
500 sq ft 1-bed: $1,800-$2,500/month
Garage conversion: $1,600-$2,200/month

At $2,000/month, you'll earn $24,000/year—paying off a $100,000 investment in about 4-5 years.

Get a Budget-Conscious Estimate

One Stop Builders works with homeowners at all budget levels. We'll help you identify the most cost-effective ADU option for your property. Call (858) 567-0007 for a free consultation.

Cheapest ADU Options in San Diego: Budget-Friendly Building Guide