ADU Cost Calculator for California: Complete 2025-2026 Pricing

How Much Does an ADU Cost in California?

ADU (Accessory Dwelling Unit) construction in California ranges from $150,000 to $350,000+ for a detached unit. Garage conversions start at $80,000-$150,000. Junior ADUs (JADUs under 500 sq ft within existing space) cost $40,000-$80,000. San Diego ADU costs average $250-$400 per square foot depending on finishes. California's streamlined ADU permitting (AB 68, SB 13) has reduced fees, but construction costs remain high due to material and labor markets.

ADU Cost Factors in California

Size: Most ADUs are 400-1,200 sq ft. Foundation: $15,000-$40,000 for new slab. Utility connections: $10,000-$30,000 (sewer lateral, electrical panel, water). Plans and permits: $5,000-$15,000. Impact fees: Waived for ADUs under 750 sq ft in most CA cities. Finishes: Budget $50-$100/sq ft for interior finishes. California requires solar panels on new construction, adding $8,000-$15,000.

Garage Conversion vs. New Build ADU

Converting an existing garage saves 30-50% compared to new construction. You skip foundation, framing, and roofing costs. A typical 400 sq ft garage conversion in San Diego costs $80,000-$150,000. However, you lose parking and may need to address the existing slab (moisture barrier, leveling). New detached ADUs cost more but offer better layouts, modern insulation, and higher rental income potential ($1,800-$2,800/mo in San Diego).

California ADU Regulations You Should Know

California law (effective 2024) allows ADUs on any residential lot. Key rules: max 1,200 sq ft for detached ADUs, 4-foot side/rear setbacks, no owner-occupancy requirement, no parking requirements within 0.5 miles of transit. San Diego specific: streamlined permits (60-day review), pre-approved ADU plans available from the city. Use our calculator to estimate costs based on your specific lot and ADU type.