State law permits ADUs up to 1,200 sqft for detached units. 6,000–9,000 sqft for standard residential neighborhoods. Hillside properties in Sunny Hills and Raymond Hills may be significantly larger. No minimum lot size required by state law to build an ADU.
Up to 16 feet for detached ADUs. Up to 25 feet for attached ADUs in qualifying residential zones.
4-foot minimum from rear and side property lines for new detached ADUs. Conversions of existing structures are exempt from setback requirements.
One parking space per ADU may be required. Exempt if within 0.5 miles of public transit (including Fullerton Transportation Center), if the property is in a designated Preservation "P" zone, or if the property is on the local historic register.
No owner-occupancy requirement for ADUs (made permanent by AB 976 in 2025).
Estimated cost $250K–$400K. Permit fees $5K–$12K. Impact fees: Waived under 750 sqft.
Fullerton is a vibrant north Orange County city of approximately 140,000 residents, defined by its relationship with Cal State Fullerton — one of the largest universities in the CSU system with over 40,000 students. The city features diverse neighborhoods ranging from the walkable downtown core with its restaurants, bars, and live music venues, to the upscale hillside homes of Sunny Hills and Raymond Hills, to established flatland neighborhoods near the university. Fullerton's Metrolink and Amtrak station connects to Los Angeles and San Diego, and the city enforces a 31-day minimum rental period on ADUs, effectively prohibiting short-term vacation rentals while supporting the long-term housing market.