California has spent several years systematically dismantling the local zoning rules that historically blocked backyard housing. The result is a regulatory environment that leans heavily toward homeowners — but one where the gap between what the law allows and what homeowners assume is still wide enough to stall projects before they start.
The most important provision is the statewide safe harbor. Regardless of local lot coverage rules, floor area ratios, or open space requirements, cities must permit at least one detached ADU up to 800 square feet and 16 feet tall, with 4-foot side and rear setbacks, on virtually any residential lot. Beyond that floor, detached units cannot be capped below 1,200 square feet, and attached units must be allowed up to 850 square feet for a one-bedroom or 1,000 square feet for two or more bedrooms. Junior ADUs carved from existing home space are capped at 500 square feet.
Setback rules shifted just as significantly. New detached ADUs require no more than 4-foot side and rear setbacks, and conversions of existing garages or structures require no setback at all — meaning a structure sitting on the property line can keep that footprint. Parking requirements have been largely eliminated: cities cannot require replacement parking when a garage is converted, and no additional parking can be required for units within a half mile of public transit.
The approval process has also changed. ADU applications are now reviewed ministerially — no public hearings, no neighbor veto, no design review board. Once a complete application is submitted, the city has 60 days to approve or deny it. Miss the deadline, and the application is deemed approved. Both the state and the City of Los Angeles maintain pre-approved plan libraries that can shorten plan check and reduce design fees.
What It Actually Costs
Construction by Maya, a Calabasas-based contractor specializing in ADU and garage conversion projects across the San Fernando and Conejo valleys, publishes 2026 pricing ranges for the Los Angeles market:
- Garage conversion (400–500 sq ft): $90,000–$160,000
- Junior ADU within existing home: $80,000–$150,000
- Small detached studio or one-bedroom (500 sq ft): $180,000–$260,000
- Mid-size detached one-bedroom (750 sq ft): $250,000–$375,000
- Large detached two-bedroom (1,000–1,200 sq ft): $350,000–$550,000+
Soft costs — design, engineering, soils reports, permit fees, and energy compliance — typically consume 10 to 20 percent of the total budget. The category that surprises homeowners most is site and utility work: sewer and water line extensions run $5,000 to $20,000, and electrical panel upgrades add another $4,000 to $12,000.
How Long It Takes
Most homeowners should plan on 9 to 15 months start to finish. Design and engineering take 4 to 10 weeks. Permitting runs 6 to 16 weeks. Construction takes 2 to 4 months for a garage conversion and 4 to 8 months for a new detached unit.
Local conditions — hillside fire zones, coastal overlays, expansive soils — can push both costs and timelines beyond standard ranges. Impact fees are prohibited statewide for units under 750 square feet, though larger units may owe them proportionally.