SB9 vs ADU: What’s the Difference and Which Is Better?

TL;DR: SB9 ADUs

SB9 ADUs are housing projects that combine California’s SB9 lot split law with accessory dwelling unit (ADU) regulations to create additional homes on a residential property. A typical SB9 project involves verifying lot eligibility, obtaining subdivision and permitting approvals, coordinating utilities, and constructing new units, which can take significantly longer and cost more than a traditional ADU project because of added zoning and legal requirements.

• SB9 is a California housing law that allows qualifying single-family lots to be split and developed with up to four primary housing units, while ADUs are secondary units added to an existing property.
• Traditional ADUs are usually simpler, faster, and easier to permit than SB9 lot split projects because SB9 developments involve stricter zoning, subdivision, and infrastructure requirements.
• SB9 projects often require additional planning reviews, utility coordination, lot split approvals, and legal documentation, which can increase timelines, complexity, and overall project costs.
• Many California properties do not qualify for SB9 because of restrictions tied to lot size, fire zones, historic districts, environmental overlays, or owner-occupancy requirements.
• Homeowners can sometimes combine SB9 with ADUs or JADUs to maximize density, rental income, or multigenerational living space, depending on local regulations and site conditions.
• This guide explains how SB9 and ADUs differ in costs, timelines, permitting, eligibility, financing, risks, and long-term property value so homeowners can better evaluate which option fits their goals.

Key Takeaways

Passed in 2021, California’s Senate Bill 9 (or SB9, for short) increased the permitted housing density throughout California in an effort to combat the state’s housing crisis by allowing a second single-family home to be built alongside an existing primary unit. In some cases, SB9 even allows an existing lot to be split, allowing four single-family homes to be built within the space where one previously stood.

While legal across the state, despite some challenges, not all municipalities readily approve SB9 applications. To date, property owners looking to add an independent living space to their lot typically opt to build an accessory dwelling unit, or ADU, rather than another primary dwelling unit under SB9, as the zoning process and city approvals for ADUs are generally easier to navigate.

Compare SB9 and ADU timelines side by side to determine which expansion path aligns with your goals.

What Is SB9 and How Does it Work?

SB9 was one of many state laws passed over the past several years aimed at increasing the availability of housing in the state. Where a lot may have previously been zoned for only a single family home, SB9 now makes it possible to put two primary residences on one residential lot.

In certain cases and under specific conditions, SB9 allows for the splitting of the lot. A split lot would mean that what was formerly a single family property could now house up to four primary residences.

To qualify for SB9:

• The property must be zoned for single-family residential use
• The lot must not be in sensitive areas like high fire risk or historic districts
• The owner must live on-site for at least 3 years if they do a lot split
• The split must result in roughly equal parcel sizes (no smaller than 40% of the original)

Remember that SB9 allows two primary units on one lot, but for most homeowners an ADU remains the simpler, quicker choice.

Is SB9 Still Legal After the LA Lawsuit?

Yes. Despite being challenged by five Southern California cities (Redondo Beach, Carson, Torrence, Whittier, and Del Mar), the state courts have upheld SB9, meaning that SB9 remains a state law throughout California.

Though the state sets the baseline regulations, municipalities can interpret the law as they see fit. This means that some cities may take a more narrow interpretation of the law, which can slow down or even inhibit the building process under SB9.

California continues updating ADU and housing legislation through 2025 and 2026 in an effort to reduce local permitting barriers and accelerate housing production. Recent updates have strengthened the state’s ability to override local ADU ordinances that conflict with state law, while also introducing stricter permit review timelines and additional streamlining measures for qualifying projects.

Even with courts upholding SB9, watch for city-specific interpretations—local variances can make or break your project.

2025–2026 California SB9 and ADU Law Updates

California continues updating housing laws to streamline ADU approvals and reduce local restrictions. Several 2025 and 2026 updates may affect how homeowners evaluate SB9 projects versus traditional ADUs.

Important Recent Changes

• Some local ADU ordinances can now be overridden if they conflict with state ADU law
• Certain smaller ADUs may qualify for reduced school impact fees
• Coastal ADU permit timelines have been shortened in some jurisdictions
• Additional permit-review deadlines now apply to local agencies
• Some owner-occupancy rules for JADUs have changed

Why These Updates Matter

These changes generally make traditional ADUs easier and faster to approve, while SB9 lot splits still remain more complex because they involve subdivision, utility coordination, and additional legal review.

Quick Answers

• Did SB9 change in 2025?
  California continues refining housing laws related to ADUs and local permitting, which indirectly affects SB9 development strategies.
• Are ADUs becoming easier to permit?
  In many cities, yes. State laws continue limiting local restrictions and requiring faster permit processing.
• Do these changes eliminate SB9 restrictions?
  No. SB9 projects still face subdivision, zoning, and environmental review requirements.
• Do local city rules still matter?
  Yes. Cities still control many implementation details, overlays, and permitting procedures.

How Many SB9 Projects Have Been Approved in San Diego?

As of late 2024 and into 2025, publicly available City of San Diego permitting data continued to show relatively low SB9 application volume and approval activity compared to traditional ADU development. Early SB9 adoption in San Diego has remained limited, largely due to the added complexity of lot splits, subdivision requirements, utility coordination, environmental overlays, and longer permitting timelines. This is according to the City’s own Permitting Center Dashboard, which provides historical data on:

• Applications Received
• Permits Issued
• Summary for Issuances
• Permits Completed

Permitting Insights for SB9 Projects in San Diego

7 out of 23 total applications is about a 30% approval rating for an SB9 project in San Diego, which is quite low. But the more interesting figure to examine is the 23 total applications over the past three or so years of SB9’s existence.

Given the size and population of San Diego, 23 total applications is surprisingly low. What we know about those who do apply, based on news reports, is that they tend to be professional builders with the means and understanding to navigate a more complicated permit process that can take 8 to 12 months, or they’re homeowners who have hired a professional to navigate the permit process on their behalf.

Recent California housing law updates have also introduced faster ADU permit review requirements in many jurisdictions, including stricter timelines for determining application completeness and processing qualifying projects. While these changes may help streamline traditional ADU approvals, SB9 lot split projects often remain substantially more complex because they still involve subdivision review, utility coordination, environmental analysis, and additional legal documentation.

To put that permit timeline in perspective, at Better Place Home & Design, we can often complete a full ADU build in 8-12 months, which includes both the design and permitting phases.

The reasons for potential SB9 application rejection are many and include:

• Zoning incompatibility, meaning the existing lot is not designated as a single family
• Environmental and hazard constraints, such as wetlands or high fire hazard
• Lot size and configuration issues, meaning the lot is not at least 2400 square feet and/or the lot splits would not be nearly equal in size
• Existing rental or affordable housing units on the property. The existence of these can prohibit SB9 approval.
• Owner-occupancy requirements, meaning the property owner is not able to be on the property for 3 years following the split
• Incomplete or non-compliant applications, meaning those that are missing required documents or do not follow local zoning laws
• Local Coastal Program (LCP) restrictions. SB9 applications in these areas face even stricter requirements than in other areas
• Public safety and health concerns, such as the impacting of emergency routes or exacerbating traffic congestion

Note San Diego’s roughly 30% SB9 approval rate—partnering with ADU experts often yields faster, more reliable results.

Common Risks and Challenges With SB9 Projects

SB9 projects can create valuable development opportunities, but they also introduce additional permitting, infrastructure, and financial complexity compared to traditional ADUs. Many homeowners underestimate how difficult lot splits and subdivision approvals can become.

Common SB9 Challenges

• Utility upgrades and separate service requirements
• Environmental overlays and fire-zone restrictions
• Longer permitting timelines
• Increased legal and surveying costs
• Financing complexity
• Easement and access issues
• Infrastructure coordination for split parcels
• HOA or neighborhood opposition
• Property tax reassessment concerns

Why Some SB9 Projects Fail

1. The property does not qualify under local overlays or environmental restrictions
2. Utility infrastructure becomes too expensive
3. Lot split requirements reduce usable space
4. Owners underestimate timeline and soft costs
5. Financing assumptions are unrealistic

Signs an ADU May Be the Better Fit

• The homeowner wants faster approvals
• Rental income is the primary goal
• The property has environmental or fire-zone restrictions
• The owner does not want subdivision complexity
• The homeowner plans to keep the property long term

Quick Answers

• Are SB9 projects risky?
  They can be significantly more complex than standard ADUs because they involve subdivision and multiple layers of permitting.
• Why are SB9 approval rates low in some cities?
  Environmental overlays, zoning restrictions, and incomplete applications commonly slow or block approvals.
• Do SB9 projects cost more than ADUs?
  In many cases, yes. Additional legal, surveying, utility, and permitting costs can increase total project budgets.
• Can SB9 projects increase property value?
  They can, especially if additional units or separate parcels are created successfully.

Eligibility Criteria for SB9 Projects

What Are the Key Requirements for SB9 Projects?

Eligibility requirements for SB9 projects as dictated by the state of California are that the existing lot must be:

• Zoned single-family (e.g., R1)
• At least 2,400 sq. ft. for a split
• Not in high-risk fire, flood, or historical zones

The City of San Diego expands on that last point a bit, saying that to qualify for SB9, a property must not be located on:

• High or very high fire severity zone
• Wetlands
• 100-year flood zone
• Floodway
• Prime farmland, or farmland of statewide importance
• Historic district or California historical resources inventory, historic property, or landmark
• Hazardous waste, or hazardous list site
• Lands identified for conservation in an adopted natural community conservation plan
• Habitat for protected species
• Lands under a conservation easement
• Delineated earthquake fault zone

In some California coastal jurisdictions, newer state legislation has also shortened ADU permit review timelines and limited certain local approval delays. However, coastal overlays and Local Coastal Program requirements can still create additional complexity for SB9 lot split projects compared to traditional ADUs.

Before applying for SB9, confirm zoning and environmental constraints—this pre-check saves time and money.

What Is the SB9 Owner-Occupancy Rule?

The SB9 Owner-Occupancy Rule states that, for lot splits specifically, the owner must agree to live in one of the resulting homes, on either lot, for at least three years.

California housing laws continue evolving around owner-occupancy requirements, particularly for ADUs and JADUs. While some newer state updates have relaxed occupancy restrictions for certain ADU configurations, SB9 lot splits still generally require owner occupancy for at least three years following subdivision approval.

Does Having an Existing ADU Affect SB9 Eligibility?

Having an existing ADU does not necessarily disqualify you from SB9 eligibility.

Without SB9 approvals, single-family homeowners are allowed to have one single-family home, one accessory dwelling unit, and one junior accessory dwelling unit (JADU) on their property. However, there are size limitations on the ADU and JADU. An ADU can be no larger than 1200 square feet, and a JADU can be no larger than 500 square feet and must be located within the home’s existing footprint.

For homeowners looking to add even more units to their property, and especially another single-family home, SB9 makes that possible, though depending on the size and location of your existing ADU, you may be limited in where or even if you can add another single-family home to your property that meets zoning standards.

What Types of Homes Can You Build After an SB9 Lot Split?

If you split your lot under SB9, you essentially have two single-family lots where there was previously only one.

This opens you up to a variety of building possibilities. You can build:

• Two single family homes on each lot
• Two duplexes on each lot
• A mixture of single family homes and ADUs, depending on the lot size & shape, as well as the  size & shape of the ADU

When planning a lot split, design your layout to accommodate the desired unit types and maximize usable space.

Can You Use SB9 to Split a Lot and Also Build an ADU?

Yes, though it can complicate an already complicated process.

Benefits of doing this include:

• Increased property value
• Increase potential rental income
• Expanded multigenerational living opportunities
• Ability to sell parcels separately (if a lot split is involved)

Challenges of doing this include:

• Even more complex application and approval processes, as SB9 and ADUs have different regulations and requirements
• Longer project timelines 
• Higher construction costs
• Potential community or HOA pushback

For the average homeowner, the ability to build a JADU and an ADU on their existing property, even without SB9 approval, often provides them with the rental income and extra living space they’re looking for without adding unnecessary complications.

When exploring SB9 plus ADU, coordinate your utility plan early to prevent costly reroutes and delays.

Can I Split My Lot Now and Decide What to Build Later?

Yes, but know that state and local laws are always changing, especially when it comes to zoning and building permit requirements, so you may be more limited in your building options later.

Planning ahead and getting building plans approved for both lots will minimize your risk and maximize your potential return on investment.

Real Examples of SB9 and ADU Development Scenarios

Every property has different zoning constraints, financial goals, and development opportunities. Comparing common project scenarios can help homeowners understand which path may fit their situation.

Example Scenarios

• A homeowner builds a detached ADU for rental income while continuing to live in the primary home
• A family uses SB9 to split a large lot and develop multiple homes for relatives
• An investor combines SB9 with ADUs to maximize unit count on a qualifying parcel
• A homeowner abandons an SB9 strategy after utility and subdivision costs become too high

Quick Answers

• Can you build both an SB9 unit and an ADU?
  Sometimes yes, depending on local zoning, lot layout, and utility access.
• Are SB9 projects better for investors?
  They are often more attractive to investors because they can create multiple primary units or separate parcels.
• Are ADUs better for homeowners?
  For many homeowners seeking rental income or family housing, ADUs are simpler and more predictable.
• Can SB9 units be sold separately?
  In some cases, yes, if the lot split is approved and legal subdivision requirements are met.

SB9 ADUs vs. Traditional ADUs: Key Differences

You don’t have to split your lot or pursue an SB9 approval to add more residential units to your property. Many homeowners find that a two-unit development through an ADU addition offers the benefits they’re looking for (increased property value, extra living space, potential rental income) while avoiding some of the biggest pitfalls (long project timelines, a more complicated permitting process, and increased property taxes).

SB9 vs SB10: What’s the Difference?

SB9 and SB10 are both California housing laws designed to increase residential density, but they work very differently. SB9 applies to qualifying single-family residential lots and allows lot splits and up to four residential units, while SB10 allows cities to voluntarily rezone certain urban parcels for up to 10 units near transit or infill areas.

Common SB9 vs SB10 Scenarios

• A homeowner wants to split a backyard lot and add multiple homes → SB9
• A city wants higher-density housing near transit → SB10
• A homeowner wants a simpler rental-income project → Traditional ADU
• An investor wants small-scale residential development → SB9 may apply

Quick Answers

• Is SB10 better than SB9?
  They serve different purposes. SB9 is designed for homeowners, while SB10 is intended for city-led multifamily rezoning.
• Can homeowners use SB10 directly?
  Not usually. Cities must first adopt SB10 rezoning ordinances.
• Does SB10 replace ADU laws?
  No. ADU laws still apply separately from SB10.
• Can you combine SB9 and SB10?
  In some cities, zoning overlaps may create additional opportunities, but this depends on local regulations.

Financing Options for SB9 and ADU Projects

Financing an SB9 project is often more complicated than financing a traditional ADU because lenders may view lot splits and multi-unit development as higher-risk projects. Homeowners should understand financing differences before choosing a development strategy.

As California continues streamlining ADU approvals through newer 2025–2026 housing laws, some lenders may view traditional ADU projects as lower-risk investments compared to SB9 developments. Faster permit timelines and simpler approval pathways can sometimes improve financing flexibility for homeowners pursuing detached ADUs instead of lot splits.

Common Financing Approaches

• HELOCs for smaller detached ADUs
• Cash-out refinancing for homeowners with strong equity
• Construction loans for larger SB9 developments
• Investor partnerships for lot splits and resale strategies
• DSCR loans for rental-income-focused projects

Financing Considerations

1. Determine realistic project costs before applying for financing
2. Understand utility upgrade and subdivision costs early
3. Verify projected rental income assumptions
4. Factor in longer permitting timelines for SB9 projects
5. Review property tax implications before finalizing budgets

Quick Answers

• Is it harder to finance an SB9 project?
  Often yes, because lenders may consider lot splits and multi-unit construction higher risk.
• Can you use a HELOC for an ADU?
  Many homeowners use HELOCs to finance detached ADUs.
• Do SB9 projects require larger down payments?
  Some lenders may require additional reserves or equity depending on project scope.
• Can rental income help qualify for financing?
  In some cases, lenders may consider projected rental income.

Evaluating the Best Path: SB9 vs. ADU

Aside from the above comparison chart, another way to determine if pursuing an SB9 application or opting for an ADU build is right for you is to ask yourself the following questions:

1. Is your property zoned single-family?

If not, SB9 isn’t an option, though an ADU might still be.

2. Do you want to split the lot?

If so, SB9 approval is your avenue to do that.

3. How many units do you want to build?

If you want to build more than two stand-alone living structures on a single-family lot (including the primary residence), you must pursue an SB9 build.

4. Are you comfortable with a potentially longer and more complex application process?

If the answer is no, avoid SB9. Even cities that have narrow SB9 interpretations often make ADU approval processes relatively streamlined, taking no more than a few months, especially with an experienced ADU builder.

5. Is owner occupancy a concern?

If you anticipate wanting to live off your existing property in the next 3 years, an ADU build is more flexible in that regard, as it does not trigger owner-occupancy rules.

How SB9 Affects Property Taxes, Resale, and Rental Income

SB9 projects and ADUs can both increase property value and rental potential, but they may affect taxes, financing, and resale differently. Homeowners should evaluate long-term financial impacts before deciding which strategy to pursue.

Financial Considerations

• ADUs often create rental income with lower development risk
• SB9 projects may create additional resale opportunities through parcel splits
• Utility and infrastructure costs can reduce SB9 profit margins
• Property taxes may increase depending on improvements and subdivision structure
• Insurance and maintenance costs may rise with additional units

Quick Answers

• Will an ADU increase property taxes?
  Usually only the new improvement value is reassessed, not the entire property.
• Can SB9 increase resale value?
  Yes, especially if the property can legally support additional homes or separate parcels.
• Which option generates more rental income?
  SB9 projects may create more total units, but traditional ADUs often produce stronger simplicity-to-income ratios.
• Do SB9 projects have higher holding costs?
  They often do because of longer timelines and additional permitting requirements.

How Better Place Design & Build Can Help

Intimidated by the SB9 process? The good news is you don’t have to pursue SB9 to increase your property value, create a secondary source of income, or house an elderly parent.

A traditional ADU build allows you to do all these things in less time and for less money than pursuing SB9, especially when you use the ADU experts at Better Place.

We tailor-make ADUs to fit a variety of use cases and budgets, and we pride ourselves on a transparent, stress-free construction process for homeowners.

Don’t dive into uncharted territory alone. Protect your investment and see what’s possible on your property by scheduling a free consultation today.

Lean on experienced professionals who manage permitting, design, and construction, streamlining your SB9 vs. ADU decision.