SB9 vs ADU Comparison: Weighing Your Options

Since taking effect in 2022, SB9 has generated significant interest by giving California homeowners new options to create housing through either an urban lot split or a two-unit development on a single-family property. While the law opened the door to additional housing opportunities, relatively few projects have successfully made it from application to completed construction.

Between March 2022 and June 2026, the City of San Diego received 66 SB9 applications, including 51 urban lot splits and 15 two-unit developments without a lot split. Of those applications, 14 have been permitted (10 lot splits and 4 two-unit developments) and 11 have been completed (10 lot splits and 1 two-unit development). More than half of all projects remain somewhere in plan check, illustrating that while interest has grown, SB9 remains largely uncharted territory in San Diego. Limited financing options, the complexity of requirements, and the lack of established precedent continue to slow adoption compared to the much more established ADU process.

Learn about how lot splits and two unit development with SB9 compare to adding accessory dwelling units (ADUs), the key provisions of the law, what is required to split your property or build multiple units, and whether you can also add an ADU after completing a lot split.

What is SB9 and How Does it Work?

In an effort to combat the housing crisis, The State of California passed Senate Bill 9, more commonly known as SB9 or the HOME Act. SB9 allows for two different kinds of actions with lots zoned as single family residential:

1. SB9 allows for converting a single family home to a duplex or adding another single family home to the lot, without requiring a lot split. This provision offers a potentially more cost-effective and less complex alternative for homeowners who wish to add another unit but prefer not to go through the process of splitting their lot. This is also referred to as two-unit development.
2. SB9 also allows for splitting a lot into two parcels, which can be developed and/or sold independently. Lots created must be roughly equally sized lots of a minimum of 1,200 square feet each. Once split, the new separate lots allow the development of a second home or the sale of the second lot.

Previously, lot split approvals would have been “discretionary” by the local jurisdiction, whereas now such action is “ministerial,” requiring no discretionary hearing or review, including compliance with the California Environmental Quality Act (CEQA).

As with many recent accessory dwelling unit (ADU) laws passed in 2017 and 2020, the goal of SB9 is to create more housing stock.

SB9 Requirements – Potential Dealbreakers

There are several important restrictions that might immediately disqualify your property from using SB9. Understanding these limitations is crucial for determining whether SB9 is a viable option for your development plans.

High-Risk Areas: Properties located in areas with high risks, such as fire zones, flood plains, earthquake zones, and hazardous waste sites, are not eligible for SB9 development. This also includes historic zones, prime farmland, conservation zones, and habitats for endangered species.

Rental Housing: SB9 housing cannot involve the demolition or alteration of housing that currently has a tenant or has had a tenant in the last three years.

Even Lot Split: The split cannot result in one very large lot and one very small lot (e.g., the split cannot be greater than 60/40).

Owner Occupancy: SB9 requires the property owner to sign an agreement that they will live on one of the lots for at least 3 years. Also, lot splits on adjacent parcels by the same individual or another party acting on their behalf are prohibited.

Lending Complications: With SB9 being so new (and unique to California), you will find most financial institutions do not have clear guidelines for dealing with SB9 lot splits. So it is unlikely that SB9 deals are easily financed, which is likely a key reason there has not been much activity in this space.

Timeline & Cost for an SB9 Project

Navigating the complexities of SB9 legislation involves a multi-phase process, from feasibility assessments to application preparation and title recording. Property owners should expect total costs to range between ~$40-70K and a timeline of approximately 4-6 months to complete all steps. Below is a detailed breakdown of the costs, services included, and timelines for each phase to help you plan effectively:

• Initiation Services: This phase focuses on assessing the parcel’s eligibility and providing a preliminary conceptual plan.
  • Estimated Cost: $3,500
  • Timeline: 2 weeks
• Preparation of Application Materials: The application preparation process is tailored to the city’s specific requirements and involves a detailed compilation of technical and regulatory documentation such as surveying, title review, and FAR calculations.
  • Estimated Cost: $20,000 to $30,000
  • Timeline: 6 to 8 weeks
•  SB9 Application Processing: Once all required documents are compiled, the formal application process begins, including submission as the owner representative, city follow-up & revisions, and final approval.
  • Estimated Cost: $10,000 to $20,000
  • Timeline: 60 days (Per State Mandate)
• Title Recording with County: The final phase includes preparing and recording the subdivision map and registering the new title with the county. Key steps include subdivision map preparation, site monumentation, and title registration.
  • Estimated Cost: $10,000 to $15,000
  • Timeline: 4 weeks

Challenges & Considerations for SB9 Projects

SB9 projects continue to carry considerably more uncertainty than ADUs. Although the City of San Diego has now received 66 SB9 applications, relatively few have completed the full permitting and construction process. As of mid-2026:

• 51 urban lot splits have been submitted, with 10 permitted, 10 completed, 28 still in plan check, 3 withdrawn, and 10 expired before receiving permits.
• 15 two-unit developments have been submitted, with 4 permitted, 1 completed, 8 still in plan check, and 3 expired before receiving permits.

City of San Diego Permit Data, March 2022 – June 2026

The data shows that homeowners have pursued lot splits much more frequently than two-unit developments. Additionally, a relatively low percentage of submissions have been officially permitted or built (for two-unit developments). Only 14 of the City’s 66 SB9 applications have received permits (21%), while 36 remain in plan check (55%) and 16 projects were either withdrawn or expired before approval (24%). Together, these figures suggest that SB9 projects often involve lengthy review timelines and that a meaningful number of homeowners ultimately decide not to move forward after beginning the entitlement process.

It is still difficult to get definitive answers from jurisdictions before submitting an application, and any SB9 project generally requires much more trial and error than a typical ADU project. While a jurisdiction may offer preliminary guidance, that guidance is rarely binding until the formal plan check process begins. To reach that point, you’ll need a full set of plans, although a few jurisdictions offer preliminary review processes. As with any relatively new law, there are still gray areas in how certain provisions are interpreted, particularly when cities encounter unique situations for the first time.

This uncertainty can lead to extended plan check timelines, additional design revisions, increased project costs, financing challenges, and, in some cases, legal disputes over interpretation of the law. Homeowners considering SB9 should proceed with caution and be prepared for a more complex and less predictable process than a typical ADU project.

While we typically build ADUs rather than primary residences, two-unit development using SB9 is an area we are willing to explore with homeowners who understand these considerations and are comfortable with the uncertainty. We are accustomed to having a high level of confidence in how each ADU project will progress. Simply by building nearly 100 ADUs, we’ve developed a strong understanding of the permitting process, common challenges, and expected outcomes.

Key Differences – SB9 vs. ADU

You may be weighing your options and wondering what is a better option for your property potential: using SB9 or adding an ADU. Check out a quick summary of the main differences when using SB9 vs adding ADUs, some of which carry significant cost implications (e.g. utility connections for new properties must be connected to a city sewer and city water on the curb’s street side… this kind of “right of way” work is extremely expensive). You’ll also want to consider the different restrictions on owner occupancy and how you can or cannot individually sell the units.

Related read: Drawbacks of ADUs? Here’s What People Get Wrong

Frequently Asked Questions About SB9

How many units can I build on my property with two unit development?

Without splitting your lot, SB9 allows up to two primary dwelling units on a single-family lot and any number of ADUs as permitted under ADU law.

If you do want to split your lot under SB9’s urban lot split provision, the math changes: state law only guarantees up to two units per resulting parcel — no more. Across the two new parcels, that’s a maximum of four total units (two per parcel).

What kind of residence can you build after a lot split with SB9?

When a lot split is utilized, a local agency must allow two units on each of the resulting lots.

Homeowners must comply with local zoning requirements when developing another single-family residence or duplex (height, floor area ratios, lot coverage, etc.), so long as those local rules don’t physically preclude construction of at least one unit of 800 square feet, or otherwise block development below the two unit per parcel cap SB9 guarantees.

While the project must comply with applicable objective zoning and design standards, those standards cannot physically prevent the lot split or the construction of the state-protected units.

Note that many cities will have requirements related to parking for new primary dwelling units, which may not be waived like many parking requirements are for ADUs (though no parking can be required if the parcel is within a half-mile of a high-quality transit corridor or major transit stop, or within a block of a car-share vehicle). Often the parking requirements include adding a garage for parking.

Can you use SB9 to split a lot and also build an ADU?

Generally, yes. The unit cap here comes from the SB9 statute itself versus individual city discretion. Under Gov. Code section 66411.7, a local agency is required to allow up to two units on each of the two parcels created by an urban lot split, but is never required to allow more than two per parcel. That means one of the two units on a resulting parcel can be an ADU or JADU instead of a second primary residence, but it can’t be added on top of a full two-unit allotment.

So if you split your lot under SB9, the realistic ceiling is four total units across both new parcels (two per parcel). This could be a primary residence and ADU on one parcel, and another primary residence and an ADU on the other parcel.

Cities do retain some ability to shape how ADUs interact with SB9 lot splits through their own ordinances. For example, the City of San Diego approved an ordinance in February 2022 that restricts ADU incentives on lot-split properties, and Oceanside‘s February 2022 revisions cap the combined total across both resulting parcels at 4 dwelling units — whether that’s achieved via two new SB9 units on the new lot, or a primary unit plus an ADU or JADU. These are examples of local agencies applying their own standards within the statutory two-units-per-parcel ceiling, not examples of cities choosing whether to allow ADUs at all on split lots. Check your local ADU code for how your jurisdiction handles this interaction.

Can I just split the lot first and then figure it out later? I don’t want to miss the opportunity in case things change.

Proceeding with an SB9 lot split before finalizing your overall development plan may not be advisable for several reasons:

Regulatory Restrictions and Compliance: Under SB9, there are specific requirements and conditions that need to be met for a lot split to be approved. This includes limitations on the size and dimensions of the split lots. Without a comprehensive plan, you might end up with a lot configuration that restricts your ability to build according to your later plans.

Financial Considerations: Lot splits and the subsequent development involve significant financial investment. Without a clear plan for development, you may face unforeseen costs or find that the lot split does not align financially with your long-term goals.

Design and Infrastructure Challenges: Planning the design and infrastructure for a split lot without a clear vision for the overall development can lead to logistical and design challenges. This could affect everything from utility connections to the practicality of construction on each individual lot.

Potential Legal Implications: SB9 has specific rules regarding owner occupancy and rental restrictions. Without a clear plan, you might inadvertently create a lot configuration that complicates compliance with these rules.

What about the LA lawsuit with SB9? Is SB9 illegal now?

In 2024, a Los Angeles Superior Court ruled that the original version of SB9 was unconstitutional as applied to five charter cities, including Del Mar. The Legislature subsequently passed SB 450, which amended the law and expanded its statement of statewide purpose.

In November 2025, the Court of Appeal reversed the trial-court judgment and sent the case back for reconsideration under the amended law. The appellate court did not issue a final decision on the constitutionality of SB9 as amended. In practice, SB9 remains in effect, and Del Mar has adopted regulations implementing the amended law.

What is SB 450?

SB 450 went into effect in January 2025 and strengthens SB9. Here are the main ways it does so:

1. Complete applications must be approved or denied within 60 days.
2. Completeness must generally be determined within 30 days.
3. A jurisdiction cannot impose special development standards on SB9 housing unless those standards are applied uniformly in the underlying zone.
4. Standards cannot prevent two 800 square foot units (pre-existing SB9 provision reinforced).
5. Standards cannot prevent the lot split from creating two lots of at least 1,200 square feet (pre-existing SB9 provision reinforced).
6. The former restriction against demolishing more than 25% of exterior walls was removed.
7. The state has clearer authority to enforce SB9.

Can I use SB9 on a multi-family property?

If the property is zoned multi-family, it is not SB9 eligible. SB9 requires single-family zoning, though the bill doesn’t technically require current single-family use. For instance, if the property is single-family zoned and a has a single-family home plus a legal non-conforming unit, it could potentially be eligible for SB9. However, cities often interpret SB9 as applying only to parcels with one unit or vacant land. This is why its important to check with your city’s planning department to learn more about their interpretation.  

How To Assess Options

Our integrated approach, which combines in-house permitting and design with our general contracting expertise, uniquely equips us to navigate the complexities of SB9 projects. This holistic model streamlines the process, making it more accessible for homeowners to consider SB9 as a viable option for their property development plans.

Want to discuss your ADU options in more detail? Set up an appointment with us to chat about your property.

The insights shared in this technical blog stem from our profound expertise in the industry, derived from our hands-on involvement in design, development, and implementation. While our utmost effort is dedicated to offering accurate and current information, it is crucial to recognize that the ADU space is continually evolving, potentially affecting the specifics discussed herein.

SnapADU aims to empower our readers with valuable insights and practical knowledge to navigate the dynamic landscape of accessory dwelling units. We encourage you to connect with our experts for personalized guidance and to remain informed about the latest advancements in the field. By staying engaged, you can adapt to the ever-changing nature of ADUs and make informed decisions aligned with your goals.