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Are There Restrictions on Building ADUs in California? (2025 Guide for Homeowners)

Accessory dwelling unit (ADU) development has become a key strategy for addressing housing shortages while giving property owners new income opportunities. But many homeowners still ask, are there restrictions on building ADUs? Yes, there are, but state law, recent reforms, and local conditions define exactly what’s allowed. In this guide, we cover the full landscape of California ADU laws, adu regulations, zoning regulations, local regulations, building codes, and how those interact with your property. We also explain how Golden State ADUs helps you convert those rules into successful adu construction projects.

Understanding the Basics: ADU, Secondary Housing Unit & Flexible Living Space

First, let’s clarify terms. An accessory dwelling unit or ADU (also called a “secondary unit” or “secondary housing unit”) is a smaller, self‑contained dwelling unit that shares the same lot or same property as your primary dwelling unit or primary residence. That could be an attached ADU, a detached ADU, a garage apartment converted from a detached garage (often called an accessory apartment), or a “granny flat.” Because ADUs are technically accessory to a primary dwelling, they must comply with rules governing their placement, size, and use in residential zoning districts or residential zones.

A key driver behind ADU popularity is that they provide flexible living space and more affordable housing options in neighborhoods already served by infrastructure. They help increase the housing stock and offer property owners a path to rental income or extra space for family members.

But like any housing addition, building ADUs is subject to zoning regulations, local laws, building codes, site plan review, and local regulations. Knowing what restrictions apply in 2025 is critical to avoid surprises, delays, or denial.

State-Level Authority: Where California ADU Laws Set the Floor

State Law Preempts Local Regulations That Conflict

Under state law and recent senate bill reforms, local governments cannot impose local rules that conflict with the minimum rights that homeowners have to construct ADUs under state statute. If a city’s local regulations violate state ADU law, those provisions are considered void. Recent reforms in 2025, including AB 2533, SB 1211, and SB 1077, enforce this principle by rendering local ADU laws inconsistent with state mandates null and void.

Cities and counties are mandated to permit ADUs and JADUs (junior ADUs) within their jurisdictions, though they are not strictly required to adopt their own ADU ordinance as long as state law provides the rights.

New California ADU Laws in 2025: Pre‑Approved Plans and Legalization

In 2025, new changes further reduce friction:

• AB 434 and AB 1332 require that by January 1, 2025, every city or county must maintain a program of pre‑approved ADU plans. These are standardized designs already cleared by the building department, so property owners can pick one and accelerate permitting.
• AB 2533 gives homeowners with unpermitted ADUs (built prior to January 1, 2020) a clearer path to legalization without harsh penalties.
• SB 1211 expands the maximum number of detached ADUs allowed on multifamily properties to eight, meaning more units can be added to larger properties, including detached structures. Additionally, AB 130 (2025) provides CEQA exemptions for many infill housing projects, indirectly benefiting many ADU proposals by reducing environmental review hurdles.

These reforms help ensure that state housing laws not only set minimum rights but also equip property owners with tools to streamline adu development and reduce delays.

Core Restrictions That Still Apply: What Local Regulations Can Control

Even though California ADU laws grant many rights, local zoning and development standards still play a role. Local governments in residential zoning districts may enforce reasonable restrictions, provided they are objective and do not effectively prohibit ADU construction. Let’s walk through the key areas of regulation property owners must track.

Size, Square Footage, Gross Floor Area & Unit Count

State law ensures that cities must allow a minimum size: at least 850 square feet for a studio or one-bedroom accessory dwelling unit, or 1,000 square feet for more bedrooms. Cities can permit larger units or impose maximums, but cannot restrict below those floors without violating adu laws.

For multifamily lots, SB 1211 allows property owners to build up to eight detached ADUs (not just one) as long as each conforms to development standards.

Height Restrictions & Roof Pitch

Height limits are a key source of friction. Under adu regulations, detached ADUs are generally limited to 16 feet in height.

However, detached ADUs within half a mile of a major transit stop or on lots with multi‑story primary dwellings or main dwellings may be allowed up to 18 feet, especially if roof pitch matches the primary structure.

Attached ADUs can be as high as 25 feet or match the height of the primary dwelling, depending on local codes.

Setbacks, Lot Coverage & Placement

Local zoning regulations may impose setback requirements from rear property lines, side yards, or front yards. A common pattern is a 4‑foot setback to side and rear for detached ADUs. Local zoning district rules also limit total lot coverage and building footprints. These rules are only acceptable so long as they allow at least one accessory dwelling unit to be built in compliance.

Existing primary residences or nonconforming structures may sometimes be reused or expanded within footprint limits, depending on local development standards.

Parking & Off‑Street Parking Requirements

Parking has traditionally been a significant barrier in ADU codes. Under modern adu regulations in California, local governments may require off‑street parking spaces, but many parking regulation burdens are now waived under certain conditions:

• If the ADU is within ½ mile of public transit, parking may be exempt.
• If the ADU is in an existing permitted structure or converted from part of your primary dwelling, parking requirements are often waived.
• Tandem parking or shared driveway parking may often count toward required parking.

Local zoning regulations may vary, so site‑specific analysis is critical.

Owner Occupancy & Use Restrictions, Rental Income & Short Term Rentals

Under the new ADU laws, owner occupancy is no longer a required condition to build or rent an ADU in most cases. Local governments cannot force the homeowner to live in the principal structure or main residence.

However, a few local regulations or city ordinances may restrict short term rentals (less than 30 days) in ADUs. If you plan to use the ADU for rental income, especially via platforms like Airbnb, it’s vital to confirm whether local adu permits or local laws allow short term leases.

Also, Homeowners Associations or CC&Rs may impose aesthetic restrictions (roof style, materials, paint color), so long as they remain objective and do not effectively kill the project.

Permitting, Timing & Review Procedures

Even where local zoning allows ADU development, the permit path introduces constraints. Key rules:

• ADU applications must be processed ministerially (no discretionary or subjective hearings) if they meet objective requirements.
• Local governments must issue a decision within 60 days of a complete application. If they do not, the permit may be deemed approved.
• Local agencies cannot require a hearing for standard compliance ADU applications.
• Local impact fees for ADUs under 750 square feet are prohibited. For larger ADUs, fees must be proportional to the ADU’s size or impact, not arbitrary.
• Cities must accept pre‑approved plans (per AB 434 / AB 1332) as part of their ADU permitting program.

The effect is that building permit processing becomes far more predictable than historically.

Building Codes, Structural & Fire Safety Standards

Every ADU must comply with standard building codes (structural, plumbing, electrical, fire, energy, mechanical). Local governments can’t relax those standards, though they can adopt objective code amendments specific to ADUs, so long as they don’t conflict with state law.

The Accessory Dwelling Unit Handbook from California gives guidance on widely accepted compliance paths.

Local jurisdictions may also require upgrades to utilities (water, sewer, electric), and local capacity constraints may influence project cost and timeline.

Special Zones: Coastal, Historic & Fire Areas

If your property lies in a coastal zone, historic district, flood zone, or fire hazard area, additional rules can apply. Extra permits or reviews may be required. That said, recent reforms including CEQA exemptions help reduce the burden for qualifying infill ADU projects.

Local rules in zoning districts with overlays must still respect the baseline rights in California ADU laws.

Steps & Strategies to Ensure Compliance & Smooth ADU Construction

Early Feasibility & Zoning Analysis

Before drafting plans or investing in engineering, assess your lot under residential zoning districts:

• Confirm whether your lot is eligible under local zoning regulations
• Determine setbacks, lot coverage, height limits, and parking rules
• Evaluate whether your lot qualifies for height exceptions (e.g. near transit)
• Check for overlays or special zones (historic, fire, coastal)

This step avoids surprises once you approach the building department.

Choosing Pre‑Approved or Custom Plans

Where available, using a pre‑approved plan can cut weeks or months from the permitting process. Since cities must maintain a catalog of them under AB 434 / AB 1332, property owners should review those first.
If your property is irregular, a custom design might be necessary, just ensure it satisfies objective standards.

Thorough Permit Package & Code Compliance

When submitting adu permits, include:

• A complete building permit package (plans, structural, MEP, site plan)
• Utility connection plans
• Documentation that parking, setbacks, and coverage comply
• Checks and waivers (where applicable) for parking or impact fees
  Golden State ADUs handles the compliance checklist so you don’t miss anything.

Navigating Unpermitted ADUs (Legalization)

If you’re dealing with an unpermitted ADU, new 2025 rules offer relief. For units built before January 1, 2020, agencies must provide a path to bring them into compliance without severe penalties.

Often, this involves preparing as‑built plans, upgrading structural or fire safety to code, and obtaining final inspections.

Avoiding Utility Delays & Infrastructure Constraints

While zoning and code are front and center, utility delays are a real risk, especially electrical, gas, and sewer. In some markets, utility upgrades or approvals (e.g. from PG&E) can delay ADU construction significantly. (In fact, builders have reported multi‑month hold ups for electric service upgrades in some regions).
Address these early by coordinating with utility providers, and factor contingencies into your schedule.

Working with HOAs & Design Review Boards

If your property is subject to Homeowners Associations, CC&Rs, or architectural review committees, you may face additional design constraints. While they cannot prohibit ADUs outright, they can enforce objective standards.
Work proactively: present your plans early, show that you comply with state law, and be willing to adjust aesthetics (roof lines, materials, glazing) to satisfy review.

Example Scenarios & What Restrictions Apply

Scenario A: A Single‑Family Lot in a Suburban Residential Zone

You own a lot with a primary residence in a suburban residential zoning district. You want to build one detached ADU behind the main house.
Restrictions you’ll face:

• Height limited to 16 feet (unless near transit, then possibly 18)
• 4‑ft side & rear setback
• Lot coverage constraints
• Parking requirements (unless you qualify for an exemption)
• Need to pass building codes, structural review, MEP systems
• Permit timeline of 60 days

Assuming the project meets all standards, local government must approve it.

Scenario B: Multifamily Lot Wanting Multiple ADUs

You own a building with 4 apartments and have room on-site. Thanks to SB 1211, you may propose up to 8 detached ADUs on the same lot (subject to compliance with each unit’s footprint, setbacks, height, utilities).
That opens a more ambitious adu development opportunity, but each unit still must satisfy building codes, site constraints, and individual permit compliance.

Scenario C: Legalizing an Unpermitted Garage Apartment

You converted your detached garage into a garage apartment years ago without permits. Today, you want to legalize it. Under AB 2533, you can submit as-built plans, bring safety upgrades to code, and obtain building permits without punitive fines (for pre‑2020 construction).
You’ll still need to ensure electrical, plumbing, fire, and structural compliance, and submit a complete permit package.

Scenario D: Planning to Use the ADU for Short-Term Rentals

You intend to rent your ADU as a vacation listing. You must check your local regulations and adu permits: some cities ban short‑term rentals in ADUs, even when residential rental is allowed.
If allowed, your ADU must comply with building codes, and your permit application may need to reflect occupancy type.

FAQs: Are There Restrictions on Building ADUs?

Can local governments still reject my ADU proposal?

No, not if your plan meets the state minimums and objective standards. Local rules must allow at least one accessory dwelling unit and cannot impose covert prohibitions.

Do I need to live in the primary structure to build an ADU?

Generally, no. Owner occupancy is no longer required for most ADU permits under state ADU laws and reforms.

How many ADUs can I build on one lot?

In a typical single‑family lot you can build one ADU plus optionally a JADU (junior unit). On multifamily lots, you may build up to eight detached ADUs under 2025 law.

How tall can my ADU be compared to my main dwelling?

Detached ADUs are normally limited to 16 feet, with 18 feet possible under transit or multi story conditions. Attached ADUs may match a 25-foot height or the height of the primary structure.

Can I convert my detached garage into an ADU?

Yes, a detached garage can be converted into a garage apartment, provided it meets setbacks, structural, and code requirements.

Do I have to pay impact fees for my ADU?

Not for ADUs under 750 square feet. For larger units, fees must be proportional to the ADU’s impact, not excessive.

What is the timeline for permit approval?

If your application is complete and meets local regulations and building codes, the local government must decide within 60 days.

Can my HOA block my ADU?

They can enforce objective design and aesthetic standards (roof shape, materials) but they cannot ban adu construction outright or impose subjective disapproval.

How Golden State ADUs Helps You Overcome Restrictions & Build Confidently

At Golden State ADUs, we understand that are there restrictions on building ADUs is more than a legal question, it’s a practical challenge our clients face every day. We offer comprehensive services to transform your property from potential to permitted:

• Feasibility & Zoning Review across Sacramento and Northern California, ensuring your lot meets zoning regulations, parking rules, and height/setback restrictions.
• Design Services using pre‑approved plan sets or custom plans that comply with both state law and local laws.
• Permit Management & Building Permit Submission to ensure your adu permits are complete, correct, and processed within the 60‑day window.
• Construction & Code Compliance to deliver your adu construction with full compliance in structural, fire, electrical, plumbing, and mechanical systems.
• Legalization of Unpermitted Units, including navigating unpermitted ADU retrofits under 2025 reforms.
• Access to financial assistance programs and technical assistance to help you successfully construct ADUs.

We’re your full-service partner from concept through move-in, so you don’t have to untangle local regulations, fight building inspectors, or guess what’s allowed.