ADU Builders California, a Sacramento based accessory dwelling unit company, is reinforcing its guidance services around California’s SB 9 and SB 10 legislative framework to help homeowners evaluate duplex conversions, lot splits, and the expanded housing opportunities these laws create. As more California property owners seek to maximize the residential potential of their parcels, the company is positioning its planning and design build expertise to support the full spectrum of SB 9 and SB 10 eligible projects across Sacramento and throughout the state.
Senate Bill 9, signed into law in September 2021 and effective January 1, 2022, fundamentally changed what single-family property owners can do with their land. For the first time at the statewide level, homeowners gained a path to split their lot into two parcels and build duplexes on each, creating the potential for up to four residential units on what was once a single-family parcel. Senate Bill 10 further enabled local jurisdictions to voluntarily upzone parcels near transit corridors and urban infill areas to allow up to ten units. Together, these laws represent one of the most significant shifts in California residential land use policy in decades.
ADU Builders California works with homeowners who want to understand what these laws mean for their specific property, how to navigate the compliance requirements local jurisdictions still impose, and how to approach feasibility, design, permitting, and construction in a way that reflects the current legislative landscape.
Understanding What SB 9 Actually Allows for California Property Owners
SB 9 creates two distinct opportunities for eligible single-family parcel owners in California. The first is the right to build a duplex on an existing single-family lot without requiring local approval beyond standard building permits. The second is an urban lot split, which allows a property owner to divide a qualifying parcel into two lots of roughly equal size, each of which can then accommodate its own duplex.
When both pathways are combined, a homeowner may be able to place up to four units on a parcel that previously allowed only one primary residence. This does not include ADUs or junior ADUs, which remain separately permitted under existing ADU law and may stack on top of SB 9 units in certain configurations depending on local interpretation.
Not every property qualifies. SB 9 includes a list of exemptions and eligibility criteria that homeowners must review before beginning any project. Properties in historic districts, earthquake fault zones, flood risk areas, fire hazard severity zones, farmland, wetlands, and other protected designations may not be eligible. Lots must meet minimum size thresholds. Owner occupancy requirements apply to lot splits, requiring the applicant to certify that they will occupy one of the resulting units as a primary residence for at least three years.
ADU Builders California helps homeowners understand whether their property qualifies, what conditions apply, and what a compliant project could realistically look like before significant investment is made in design or permitting.
How SB 10 Creates Opportunities Near Transit and Infill Areas
While SB 9 operates as a statewide override of single-family zoning, SB 10 takes a different approach. SB 10 allows local jurisdictions to adopt ordinances that voluntarily permit up to ten residential units on parcels located near high-quality transit corridors or in urban infill zones, even if existing zoning would not otherwise allow that density.
SB 10 does not create a right that homeowners can invoke directly. Instead, it clears state legal obstacles that would otherwise prevent local governments from upzoning through streamlined ordinance adoption, including the ability to override the California Environmental Quality Act for qualifying projects. For homeowners in cities and counties that have adopted SB 10 ordinances, the impact can be significant. Parcels near major bus routes, light rail stations, and transit hubs may become eligible for denser residential development under local rules that SB 10 made possible.
ADU Builders California monitors developments across Sacramento and other California jurisdictions to help clients understand whether SB 10 ordinances have been adopted in their area, what density levels are permitted, and how a project in a transit-proximate location might be planned in compliance with both local SB 10 rules and state building requirements.
In the middle of a rapidly evolving legislative environment, ADU Builders California continues to help property owners understand the practical implications of SB 9 and SB 10 for their specific parcels, connecting current California housing law with actionable planning, design, and construction guidance.
Navigating Local Standards That Still Apply Under SB 9
One of the most important points for California homeowners to understand is that SB 9 limits local government authority to reject eligible projects, but it does not eliminate all local review or objective design standards. Local jurisdictions retain the ability to impose objective standards related to unit size, setbacks, lot coverage, design compatibility, parking, and access, as long as those standards do not effectively preclude the development the law is intended to allow.
This creates a landscape in which Sacramento homeowners may find that their local jurisdiction has adopted SB 9 objective design standards that differ from neighboring cities. Some jurisdictions have developed specific criteria related to unit size minimums and maximums, primary frontage setbacks, rear yard setbacks, minimum lot width after a lot split, utility connection requirements, and access easements. Homeowners who approach an SB 9 project without understanding local standards risk designing plans that require revision during plan check.
ADU Builders California works to align early project planning with both the statewide SB 9 framework and the specific objective standards adopted by the relevant city or county. This includes reviewing setback requirements for new structures on split parcels, evaluating how existing infrastructure on the lot may affect development feasibility, and helping homeowners understand what documentation will be required for a ministerial permit application.
Ministerial approval is a key feature of SB 9. Unlike discretionary approvals that allow local agencies to weigh subjective criteria, ministerial permits must be approved if objective standards are met. Homeowners who prepare complete, code-compliant applications consistent with SB 9 requirements have a significantly clearer path to approval. The challenge is knowing exactly what completeness means for a specific jurisdiction.
Duplex Conversion Planning Under the SB 9 Framework
For homeowners whose properties do not qualify for a lot split, or who prefer to develop a duplex on their existing parcel without subdivision, SB 9’s duplex conversion pathway provides a direct route to adding a second unit to a single-family lot.
A duplex conversion under SB 9 can take multiple forms depending on the existing structure and site conditions. Some homeowners convert a single-family home into a legal duplex by adding a second unit within the existing building envelope. Others construct a new attached addition to create a second full unit. Still others look to replace or expand accessory structures to create a compliant second residence.
ADU Builders California evaluates each property individually to identify which duplex configuration is most feasible given the existing structure, lot dimensions, utility access, local setback requirements, and the homeowner’s specific goals. Factors such as existing foundation conditions, structural framing, electrical capacity, plumbing layout, and fire separation requirements all influence which approach is most practical and cost effective.
California building code requires that each unit in a duplex meet habitability standards, including minimum room sizes, ceiling height, natural light, ventilation, egress windows or doors, smoke and carbon monoxide detection, and accessible sanitation facilities. Energy compliance under Title 24 applies to all newly constructed or extensively remodeled residential space. ADU Builders California incorporates these standards into project planning from the earliest feasibility stage.
Lot Split Feasibility and the Urban Lot Split Process
The urban lot split pathway under SB 9 is one of the most transformative residential development tools available to California homeowners, but it also involves the most complex set of requirements. A successful lot split requires careful evaluation of parcel dimensions, existing structure placement, access and easement conditions, utility service points, and local objective standards.
SB 9 requires that each resulting parcel from an urban lot split be at least 1,200 square feet. The law also prohibits lot splits that would require the demolition or alteration of affordable housing, rent-controlled housing, or units that have been occupied by tenants within the previous three years. Properties that have already been through a previous SB 9 lot split are not eligible for another. These restrictions are designed to prevent displacement while still expanding housing supply.
For qualifying parcels, the process begins with a map application submitted to the local jurisdiction. This is separate from and must precede the building permit applications for any new structures on the resulting lots. ADU Builders California helps homeowners understand the sequence of approvals required, what a parcel map application must contain, and how to coordinate the lot split process with design development so that both proceed efficiently.
Once a lot split is recorded, each new parcel may be developed with up to two units under SB 9. The combination of a lot split with duplexes on each resulting parcel can produce four units on what was once a single-family property. Homeowners interested in this level of development benefit from early coordination between the map application process and the architectural and engineering plans for the proposed structures.
Connecting SB 9 and SB 10 Projects with ADU and Junior ADU Opportunities
California’s housing laws do not operate in isolation. SB 9 projects can in some circumstances be combined with ADU and junior ADU development to further increase housing capacity. Depending on local interpretation and the specific configuration of the project, a homeowner who completes an SB 9 lot split may be able to place an ADU and a junior ADU on each resulting parcel in addition to the primary duplex units, potentially allowing six or more units where only one previously existed.
The interaction between SB 9 and ADU law is an area where local jurisdictions have varying positions, and state guidance has continued to evolve. Some cities have attempted to limit ADU development on SB 9 parcels, while the state’s Department of Housing and Community Development has issued guidance indicating that ADU law applies independently of SB 9 and cannot be restricted based solely on the fact that an SB 9 development is occurring.
ADU Builders California helps homeowners understand the current state of this legal landscape and what combinations of housing units may be achievable on their specific property. The goal is to help clients evaluate their options fully before committing to a development path, so that the chosen approach reflects both what the law allows and what makes practical sense for the homeowner’s property and long-term goals.
About ADU Builders California
ADU Builders California is a California accessory dwelling unit company based in Sacramento. The company provides ADU planning, design build coordination, garage conversion support, detached ADU construction guidance, permitting assistance, and residential construction services for homeowners seeking additional living space. Its work focuses on practical layouts, code-compliant planning, long-term property value, and modern California housing needs, including SB 9 and SB 10 compliance support for duplex conversions and urban lot splits.
ADU Builders California
1610 R St Suite 300, Sacramento, CA 95811, United States
Phone: (916) 318-5851
