Fullerton, CA Accessory Structures: ADU Rules (2026)
ADU rules in Fullerton, CA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Max detached ADU size
- 1,200 sq ft
- Max attached ADU (2+ bed)
- 1,000 sq ft
- Standard height limit
- 16 ft detached
- Near-transit height bonus
- 18 ft, +2 ft roof pitch
- Review deadline
- 60 days (30 if preapproved plan)
- ADUs per single-family lot
- 1 ADU + 1 JADU
Summary
Fullerton allows one accessory dwelling unit and one junior ADU on any lot zoned for single-family or multifamily use, including O-P lots with an existing house. Detached ADUs top out at 1,200 square feet and 16 to 18 feet in height, with the city required to approve or deny complete applications within 60 days.
(D) Allowed zones. An ADU is permitted on any lot where single-family or multifamily dwellings are a permitted use including planned residential development districts and specific plan areas. An ADU is also allowed on a lot where a single-family or multifamily dwellings are a conditionally permitted use, provided that the lot contains or will contain either a single-unit or multifamily dwelling. An ADU is also permitted on properties zoned O-P (Office Professional) which are currently improved with a single-family dwelling unit.
Full Breakdown
100(D) permits an ADU on any lot where single-family or multifamily dwellings are a permitted or conditionally permitted use, plus O-P (Office Professional) lots already improved with a single-family home. Section (E) caps most single-family lots at one ADU and one JADU, though R-1 and R-2 lots of at least one acre with an existing single-family home can qualify for up to two detached ADUs or one attached and one detached ADU under (E)(1), subject to demonstrated sewer and water capacity. Height limits under (F)(2)(a) run 16 feet for a standard detached ADU, 18 feet if the lot sits within a half-mile of a major transit stop (plus 2 feet for a matching roof pitch), 18 feet for ADUs on multifamily/multistory lots, and 25 feet (or the zone's height limit, whichever is lower) for an attached ADU, capped at two stories.
Size limits under (F)(4)(a) are 850 square feet for an attached studio or one-bedroom, 1,000 square feet for two-plus bedrooms, and 1,200 square feet for a detached unit, with no cap on converting an existing accessory structure over that size or on an interior ADU built within the existing home. The Development Services Department must ministerially approve or deny a complete application within 60 days under (B)(1), and the application is deemed approved if the city misses that deadline; using a city-preapproved plan shortens the clock to 30 days.
Violations & Fines
An ADU built or occupied without the required building permit and Development Services approval is subject to the city's standard building code enforcement and permit correction process; the code bars the city from denying or conditioning ADU approval on correcting unrelated nonconforming zoning conditions (§ 15.17.100(B)(4)-(5)).
Frequently Asked Questions
Can I build an ADU on any residential lot in Fullerton?
How tall can a detached ADU be in Fullerton?
How long does the city have to approve my ADU application?
Sources & Official References
Other rules in Fullerton
How Fullerton compares: Easiest Cities to Build an ADU·California rules heatmap·Compare Fullerton to another location·View the California accessory structures overview
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ADU Rules in Nearby Cities
How other cities in Orange County handle adu rules.