One County, Two Sets of Rules.
First, a critical distinction: LA County's ADU ordinance only governs unincorporated areas, the communities where the Board of Supervisors acts as the city council. Per LA County Planning, more than 65 percent of the county's land is unincorporated, spanning over 2,600 square miles and roughly 120 to 125 communities, from Altadena and East Los Angeles to Topanga, Hacienda Heights, and the Antelope Valley.
The county's 88 incorporated cities, including Los Angeles, Long Beach, Pasadena, Santa Monica, and Torrance, each adopt their own ADU ordinance and run their own permit counters. County rules do not apply inside city limits. If you are not sure which jurisdiction your parcel falls under, check your lot with Abodu and we will confirm exactly which rules govern your address.
What You Can Build in Unincorporated LA County.
The county's adopted ADU Summary allows a new detached ADU of up to 1,200 square feet on a single-family lot, with 4-foot side and rear setbacks and a height limit of 25 feet for new construction accessory to a single-family home, unless a Community Standards District or Specific Plan sets a lower cap. A single-family lot can combine a detached ADU with a junior ADU (JADU) of up to 500 square feet inside the main house.
State law adds a guaranteed floor: the county must ministerially approve one new detached ADU of up to 800 square feet at 16 feet tall with 4-foot side and rear setbacks on any lot with an existing or proposed single-family home, and no development standard may be imposed that would physically preclude an 800 square foot ADU. ADUs are permitted wherever single-family or multifamily residences are allowed, and an ADU does not count against lot coverage, floor area ratio, or open space requirements.
Multifamily Lots Can Add Even More.
Unincorporated LA County follows the state framework for multifamily properties: owners can convert non-livable space such as storage rooms, garages, and basements into at least one ADU and up to 25 percent of the existing unit count, and separately add up to two new detached ADUs per property with 4-foot side and rear setbacks at 16 to 18 feet in height, per the county's ADU Summary.
For owners of duplexes, apartment buildings, or portfolios across the county's unincorporated communities, that math turns underused yard space into new rentable units. Abodu builds for this at scale: see our multifamily program.
Permits, Pre-Approved Plans, and Overlays.
Applications for unincorporated areas run through two county departments: Regional Planning reviews zoning first, then Public Works Building and Safety handles plan check, both through the online EPIC-LA portal. The county also offers a Pre-Approved ADU Standard Plans Program with three county-owned plans, two 1,200 square foot layouts and one 800 square foot layout, free to use, which is exactly the kind of repeatable, pre-engineered approach Abodu's factory-built homes are designed around.
Overlays matter in this county. In a Very High Fire Hazard Severity Zone, one off-street parking space is required for the ADU (with several state exemptions) and lots generally need two means of access to a highway, though the statewide-exemption ADU types are excused from the access rule. In the coastal zone, the applicable Local Coastal Program governs. Outside fire hazard zones, no parking is required for an ADU, and no parking is ever required for a JADU. Note the county is also evaluating a 2026 ordinance amendment that would clarify pathways for up to four accessory units on a single-family lot; it is a proposed draft, not yet law. California ADU law, summarized by HCD, requires ministerial review, and the county's own guidance references the standard 60-day review timeline for standalone ADU applications.
What It Actually Costs.
Custom site-built ADUs in California routinely exceed $250,000 before change orders, and sprawling county lots with fire, access, and septic considerations can push budgets further. Abodu works differently: transparent published pricing: homes from $234,800 plus a published installation price, an expected all-in from $298,800 that covers design, permits, factory build, delivery, and installation. No surprise line items, no open-ended timelines.
See how the process works, browse what real homeowners say on our testimonials page, or start by checking your lot.