California ADU Law: What Cities Can and Cannot Require

The single most useful thing to understand about ADU law is that a conforming application is not a request. State ADU law - originally Government Code Section 65852.2, since recodified into Government Code Section 66310 and the sections following it - requires local agencies to approve compliant ADUs ministerially.

That means no planning commission, no public hearing, no neighbour notification, no design review board exercising taste, and no conditions invented during review. Cities apply objective standards only: numbers and measurable criteria written in the code beforehand.

It also means a deadline. The agency must act on a complete application within 60 days. If it does not, the application is deemed approved in most circumstances.

In the City of Los Angeles, the implementing rules sit in Ordinance 186,481, codified at LAMC 12.22 A.33. Every city has its own implementing ordinance, and some of them still contain provisions that state law has since overridden.

State law guarantees a minimum envelope that no local standard may reduce below.

**Size.** A city must allow at least 800 square feet. Lot coverage, floor area ratio, open space and minimum lot size rules cannot be applied to block an 800 square foot ADU that otherwise meets height and setback limits.

**Height.** At least 16 feet for a detached ADU. Up to 18 feet where the lot is within half a mile walking distance of a major transit stop or has an existing multistorey multifamily building, with additional height permitted to match the primary roof pitch. Up to 25 feet, or the zone's limit if lower, for an ADU attached to the primary dwelling.

**Setbacks.** Four feet from side and rear property lines. An ADU converted from existing permitted space keeps whatever setbacks that structure already has, even at zero.

Those numbers are floors, not targets. Cities may be more generous, never less.

This list is where most homeowner-versus-counter disputes get resolved.

**Owner occupancy.** Cities cannot impose an owner-occupancy condition on an ADU. Junior ADUs - the small units created within the walls of the existing house - are the exception and still carry it.

**Replacement parking.** Convert a garage or carport to an ADU and the city cannot make you rebuild the lost parking spaces elsewhere on the lot.

**Parking generally.** No parking may be required where the ADU is within half a mile walking distance of public transit, is part of the existing primary residence, is in a historic district, is in a permit-parking area, or is within one block of a car share vehicle.

**Fire sprinklers.** Not required for the ADU if the primary dwelling is not sprinklered.

**Unrelated corrections.** A city cannot condition ADU approval on correcting unpermitted conditions elsewhere on the property, unless the condition is a genuine health and safety hazard.

**Impact fees** on ADUs under 750 square feet; above that, fees must be proportional to the primary dwelling.

The law is not a blank cheque, and reasonable requirements survive.

**Objective design standards.** Roof form, exterior materials, window placement, entry orientation - as long as they are written, measurable and applied consistently.

**Standards within the state floor.** Front setbacks, height beyond the guaranteed minimum, and separation between structures, provided they do not prevent an 800 square foot ADU at 16 feet with four-foot side and rear setbacks.

**Utility connections.** For a new detached ADU, a city or utility may require a separate connection and charge a proportional capacity fee. For a conversion within existing space, it generally may not.

**Building code compliance.** Full California Building, Plumbing, Electrical and Energy code compliance, including Title 24 and, for a new detached unit, solar photovoltaics.

**Overlay rules.** State ADU law does not waive Coastal Development Permits in the Coastal Zone, Very High Fire Hazard Severity Zone construction requirements, or hillside grading rules. Those still apply on their own terms.

Construction first. A detached ADU in Southern California runs $150,000 to $400,000 or more, or roughly $350 to $550 per square foot depending on finish level, site access and whether utilities have to be trenched a long way. A garage conversion runs $80,000 to $180,000 because the shell, slab and often the roof already exist.

Then the paperwork stack, which surprises people. In Los Angeles, plan check and permit fees for a detached ADU commonly total $6,000 to $15,000. Add a sewer facilities capacity charge, utility connection fees for a new detached unit, and school district fees, which apply to ADUs of 500 square feet and above.

On top of that sit the consultants: Title 24 energy calculations $400 to $900, HERS testing $600 to $1,200, structural engineering $1,500 to $5,000, a survey where setbacks are tight $2,000 to $5,000, and solar photovoltaics $5,000 to $12,000 on a new detached unit.

The sequence that works: confirm the lot's zoning and any overlays first, then order a survey if setbacks are tight, then design to the objective standards, then submit a complete ministerial application with the Title 24 documentation attached.

"Complete" matters, because the 60-day clock runs from a complete application. An incomplete submittal restarts it, so a thorough first submission is faster than a fast one.

If a city asks for something state law prohibits - a public hearing, owner occupancy, replacement parking for a converted garage, sprinklers your main house does not have - put the request in writing and ask which code section authorises it. That alone resolves most of them.

If it does not, the Department of Housing and Community Development reviews local ADU ordinances and can issue technical assistance letters and refer non-compliant jurisdictions for enforcement. Homeowners can and do submit complaints.