California ADU Rules Explained

Notice: This guide is for informational purposes only and does not constitute legal advice. California housing laws are subject to frequent legislative updates; always consult with a qualified land-use attorney, local planning department, and the applicable utility agency for property-specific feasibility.

Accessory Dwelling Units (ADUs) can be a major inventory-growth lever in California — but “ADU potential” is also one of the easiest ways for an agent to create liability if it’s marketed like a guarantee. This guide is part of our California Real Estate Laws & Compliance Guide and focuses on what agents need most: the state’s ministerial (no-hearing) process and the administrative “shot clocks” designed to prevent permit stalling — plus the exact items you should verify in writing before you talk numbers.

Fast Answer: What California ADU Law Actually Does

California’s ADU framework is no longer “local preference.” It’s a state-enforced ministerial system: cities must approve ADU applications that meet objective standards, and they must process them on strict timelines.

“Ministerial” just means that there’s a checklist that has to be followed, and as long as everything on that checklist is done the approval doesn’t require a hearing. However, it’s still not a guarantee until the city confirms the application is complete and compliant.

The two clocks agents should know:

1) Completeness clock (15 business days)

Cities have a 15-business-day window to determine whether an application for an ADU is complete. If the permitting agency does not make a timely completeness determination, the application is treated as complete for timing purposes and the next clock starts.

VERIFY IN WRITING (do this every time):

• Get a portal timestamp / receipt confirmation showing the submission date and time.
• If submitted by email/mail, keep proof of receipt (and ask the agency to confirm the “received” date in writing).

2) Decision clock (60 days after complete)

Once an application is complete, the city generally has 60 days to approve or deny it. Missing that deadline can trigger “deemed approved” status, subject to the statutory mechanics (and tolling if the applicant requests delay).

VERIFY IN WRITING:

• Ask the city (email is fine) to confirm the “complete” date that starts the 60-day clock.
• If the city denies, request the full written set of correction comments (all departments) in one package — not piecemeal.

Key Considerations

1) State law sets the baseline (and limits local games)

State ADU law preempts conflicting local standards. Cities can add rules, but they must stay within the state framework and use objective standards — not subjective “we don’t like it here” discretion.

VERIFY IN WRITING:

• Request the city’s current ADU ordinance + ADU handout/checklist (many cities have an “ADU packet”).
• If staff cites a rule that seems to conflict with state standards, ask them to identify the code section in writing.

2) The 60-day clock is real — and denials must be “complete”

If the city denies, it must provide a full written set of correction comments describing what’s wrong and how to fix it. This is designed to prevent the “drip-feed denial” tactic.

VERIFY IN WRITING:

• Please provide the complete set of correction comments from all reviewers and confirm this is the full list.

3) Parking: stop making promises; use exemptions carefully

Parking rules are often 0 spaces in common scenarios (especially conversions) but be sure to confirm local and state rules.

• Parking may be capped and often waived under specific statutory exemptions (transit proximity, conversion of existing space, historic district rules, permit restrictions, etc.).
• Replacement parking is often not required when converting certain existing parking structures — but don’t market that as universal without city confirmation.

VERIFY IN WRITING:

• Ask planning to confirm how many parking spaces are required for the specific property and why (which exemption they’re applying).

4) Fees: impact fees ≠ utility connection/capacity charges

This is where agent marketing can get folks in hot water.

• Impact fee rules can depend on ADU size thresholds and local fee programs.
• Utility connection/capacity charges are a separate universe (water/sewer/power) and can still surprise owners even when impact fees don’t.

VERIFY IN WRITING:

• City: “What impact fees apply for an ADU of approximately ___ sq ft?”
• Utilities: “What connection/capacity charges apply and under what calculation method?”
• Consider brushing up on Water Rights & Easements in California Real Estate (because easements + utility constraints are where projects can fall apart.

5) Short-Term Rentals (Airbnb): keep the warning, tighten the language

• California law requires 30+ day rental terms for JADUs and for ADUs approved under the § 66323 “state standards” pathway.
• For ADUs approved under a local ordinance, state law gives cities the authority to require 30+ day terms — and many jurisdictions do.

VERIFY IN WRITING:

• Never market “ADU short-term rental income” unless you have the city’s short-term rental rule in writing for that parcel.

Agent Tip: To protect your commission and your client, never market “ADU short-term rental income” unless you have verified the city’s specific STR ordinance in writing.

6) Environmental overlays and recorded easements are the silent killers

Most “ADU denials” aren’t philosophical. They’re constraints: hillside grading, coastal, fire severity, biological, historic, sewer/water limitations, or recorded easements.

VERIFY IN WRITING:

• Ask the city: “Are there any overlays affecting ADU placement (hillside/coastal/fire/historic/biological)?”
• Confirm easements on the prelim/title report before promising anything.
• Environmental Regulations California Agents Should Know
• Water Rights & Easements in California Real Estate

7) The SB 9 Intersection: When ADUs Aren't Enough

If a client wants more than just an ADU, they may ask about SB 9. While ADUs add "accessory" units, SB 9 allows for primary density increases through ministerial lot splits and two-unit developments.

Summary of SB 9 (2025-2026 Updates):

• The "Two-Unit" Rule: On a single-family lot, an owner can ministerially build two primary units (effectively a duplex) instead of a house + ADU.
• The "Urban Lot Split": SB 9 allows a single lot to be split into two. Each new lot must be at least 1,200 sq ft.
• The "Unit Cap" Trap: If a lot is split under SB 9, the city can limit the total number of units to two per new lot (inclusive of ADUs/JADUs).This means you generally cannot "stack" an SB 9 lot split with multiple ADUs to get 6 or 8 units unless the local ordinance specifically allows it.
• Owner-Occupancy (The Big Catch): Unlike ADUs, an SB 9 lot split requires the owner to sign an affidavit stating they intend to occupy one of the units as their primary residence for at least three years.

VERIFY IN WRITING:

• "Does this specific parcel qualify for an SB 9 lot split (check for historic districts/fire zones)?"
• "If we split the lot, what is the maximum total unit count (including ADUs) allowed per parcel?"

8) The Rental Strategy Trap: Rent Control & AB 1482

This is a critical due diligence item for investors. While a single-family home (SFH) is typically exempt from statewide rent control under the Costa-Hawkins Rental Housing Act, adding an ADU can change that.

Rental strategy trap (state + local): don’t underwrite rents in your head.

If a client wants more than just an ADU, they may ask about SB 9. While ADUs add "accessory" units, under AB 1482 depending on the property type, ownership structure, and required tenant notices

VERIFY IN WRITING: Before you market “rent upside,” have the buyer/owner confirm (a) whether the property is covered by a local rent stabilization ordinance, and (b) whether AB 1482 applies or an exemption applies — preferably with a landlord-tenant attorney or written guidance from a credible local housing/rent authority.

“What to Say in Listing Remarks” (safe, punchy, defensible)

Use language like this:

Property may be eligible for an ADU (subject to city review, utility capacity, and recorded easements). Buyer to verify ADU feasibility, fees, parking, and rental restrictions with the City and utility providers.

Avoid language like:

• “Guaranteed ADU”
• “By-right ADU” (unless you’re prepared to prove the exact pathway + objective compliance)
• “No fees”
• “No parking required”
• “Airbnb income”

The shift from local control to a state-mandated ADU framework has created a massive opportunity for California homeowners, but for real estate agents, it has also moved the goalposts for professional liability. Mastering ADU rules is no longer just about knowing square footage; it is about protecting your clients from expensive permitting delays and "soft" denials.

As we move through 2026, the key to a successful ADU-focused transaction is transparency. By using the "administrative shot clocks" provided by SB 543 and the streamlined pathways of AB 1154, you can help your clients navigate the process with confidence—provided you never mistake "potential" for a "guarantee."

Your Starter Checklist for Every ADU Listing:

• Don't Guess on Fees: Get the city’s impact fee and the utility’s capacity charge schedules in writing.
• Watch the Clock: Use timestamped receipts to hold agencies to their 15-business-day and 60-day legal windows.
• Build the Professional Team: Always refer your clients to a qualified land-use attorney, a licensed architect, and a contractor to confirm site-specific feasibility.

Staying "compliance-first" is what separates top-tier agents from the rest. By facilitating the right conversations with the right experts, you protect your commission, your reputation, and your client’s investment.