If you own a single-family home in Campbell, the question of whether to build an Accessory Dwelling Unit has probably crossed your mind more than once. The economics make it compelling: rental income that offsets a mortgage, housing for an aging parent or adult child, or simply a long-term investment in a property that’s already among the most valuable assets most California families hold. ADUs have gone from obscure zoning footnote to mainstream conversation piece in the South Bay, and for good reason. State legislation passed over the last several years has dramatically streamlined the process and expanded what’s allowed.
But streamlined doesn’t mean simple. Even with California’s aggressive push to remove ADU barriers at the state level, local jurisdictions retain meaningful authority over specific requirements — setbacks, height limits, utility connections, design standards — that directly affect what you can build on your property in Campbell. Understanding these requirements before you begin is not just a procedural formality. It’s the difference between a project that moves forward efficiently and one that stalls at plan check because the design doesn’t match what the City actually allows.
This guide breaks down the key ADU requirements in Campbell so homeowners can approach the process with a clear picture of what’s possible, what’s required, and where the most important decisions need to be made.
How California State Law Sets the Foundation
Before getting into Campbell’s specific requirements, it helps to understand the framework that governs ADUs statewide. The California Department of Housing and Community Development administers the state’s ADU statutes, which were substantially updated through a series of bills — most notably AB 68, AB 881, SB 13, and AB 2221 — that took effect between 2020 and 2023. These laws placed significant limitations on what local governments can prohibit or restrict when it comes to ADUs.
The practical effect is that cities and counties, including Campbell, cannot prohibit ADUs outright in single-family residential zones. They cannot impose minimum lot size requirements that effectively eliminate most properties from eligibility. They must approve ministerially — meaning without a public hearing — any ADU application that meets the objective standards in place. And they must act on a completed ADU application within 60 days. These are meaningful protections for homeowners that make the California ADU landscape more accessible than it was even five years ago.
What state law does not do is eliminate local requirements entirely. Campbell has adopted its own ADU ordinance that establishes the specific standards applying within city limits — and knowing those standards is essential before finalizing any design or entering the permitting process.
Types of ADUs Permitted in Campbell
Campbell’s ADU ordinance recognizes several distinct types of accessory dwelling units, and the requirements differ meaningfully depending on which type you’re building.
A detached ADU is a fully independent structure separate from the primary home. These offer the greatest design flexibility and privacy for both occupants, but they also involve the most complex construction since they require independent foundation, framing, roofing, and typically separate utility connections. Animas Valley Construction’s work with detached ADUs covers exactly this type — purpose-built structures designed to function as complete independent living spaces.
An attached ADU shares one or more walls with the primary residence. It’s built as an addition to the existing home rather than as a separate structure, and it can be a practical option for properties where lot configuration makes a detached structure difficult to position within setback requirements.
A garage conversion ADU converts an existing attached or detached garage into habitable living space. This is one of the most cost-effective ADU approaches because the structure already exists — foundation, walls, and roof are already in place — and the project primarily involves interior conversion plus upgraded insulation, electrical, and mechanical systems. Campbell’s ADU rules align with the state’s prohibition against requiring garage replacement when a garage conversion ADU is built, which means homeowners don’t have to build a new garage to replace the converted one. Learn more about this path through Animas Valley Construction’s garage conversion ADU services.
A Junior ADU (JADU) is a smaller unit created entirely within the existing footprint of the primary home, typically from a bedroom with a private exterior entrance. JADUs are capped at 500 square feet and share bathroom facilities with the main home in many configurations. They’re the most limited in scope but also the most accessible for homeowners who want a rental unit with minimal new construction. Animas Valley Construction has dedicated resources on JADUs for homeowners exploring this option.
Size Limits, Setbacks, and Height Requirements
The dimensional requirements that apply to ADUs in Campbell reflect a combination of state minimums and locally adopted standards. Understanding these early is critical because they directly influence site planning and what’s achievable on a given lot.
For detached ADUs in single-family zones, Campbell follows state law in establishing a maximum size of 1,200 square feet for units with more than one bedroom. State law also guarantees a minimum allowable size of at least 850 square feet for a studio or one-bedroom unit and 1,000 square feet for a unit with more than one bedroom, regardless of other local limitations. This means even properties with smaller lot coverage allowances can support a meaningful ADU.
Setbacks — the required distances between the ADU structure and property lines — are another area where state law has narrowed local discretion. For the rear and side setbacks of a detached ADU, the California Department of Housing and Community Development’s guidelines limit local agencies from requiring setbacks greater than four feet. This is a significant change from prior requirements and opens up a much larger portion of most residential lots for potential ADU placement. Front setbacks are typically governed by the same standards that apply to the primary structure’s setback from the front property line.
Height limits for detached ADUs in California follow state minimums that require cities to allow at least 16 feet for detached ADUs on single-family lots, and up to 18 feet if the property is within half a mile of a major transit stop. Campbell’s local standards apply within this framework, and the specific height limit applicable to your project should be confirmed with the City of Campbell Community Development Department early in the design process, as it can affect the roof form and overall design of the structure.
Utility Requirements: Water, Sewer, and Energy
Utility connections are one of the most significant cost variables in an ADU project and one of the areas where homeowners most frequently encounter surprises. Understanding what’s required — and what state law now limits — before budgeting is essential.
For attached and detached ADUs, utility connections to water and sewer are required. California state law, however, prohibits local agencies from requiring a new or separate utility connection between the ADU and the street for conversions of existing space — including garage conversions — when the ADU is not proposed as part of a new primary dwelling. This means a garage conversion ADU can typically connect to the existing home’s utility lines rather than paying the often-substantial cost of a separate lateral connection to the street main.
For new detached ADUs, a separate utility connection may still be required in some cases, though impact fees have also been significantly limited by state legislation. ADUs under 750 square feet are exempt from water and sewer capacity charges. For those above 750 square feet, fees must be proportionate to the impact of the ADU relative to the primary home rather than calculated as a full new connection. This fee limitation can represent a meaningful reduction in project cost for homeowners building larger detached units.
Energy code compliance is governed by California’s Title 24 Building Energy Efficiency Standards, and all ADU projects — new construction or conversion — must demonstrate compliance with applicable energy requirements. For new detached ADUs over a certain square footage threshold, this may include solar panel installation requirements consistent with California’s mandate for new residential construction. Your designer and contractor will confirm the applicable energy code requirements for your specific ADU scope.
ADU Requirements Summary Table
| ADU Type | Max Size | Min Rear/Side Setback | Min Height Allowed | Separate Utility Connection Required |
|---|---|---|---|---|
| Detached ADU | 1,200 sq ft | 4 feet | 16–18 feet (varies) | Typically yes for new construction |
| Attached ADU | 50% of primary home or 1,200 sq ft | Matches primary dwelling setbacks | Matches primary structure | Tied to primary home connection |
| Garage Conversion ADU | Existing garage footprint | No additional setback required | Existing structure height | No new lateral required (state law) |
| Junior ADU (JADU) | 500 sq ft | Within existing primary structure | Within existing structure | Shared with primary home |
What the Permitting Process Involves
All ADU projects in Campbell require a building permit issued by the City of Campbell Community Development Department. The application includes architectural drawings showing the proposed layout, elevations, site plan, and any structural or mechanical modifications. Projects involving new construction also require a structural engineering package.
State law requires Campbell to act on a complete ADU permit application within 60 days. If the application is incomplete, the city has 30 days to identify deficiencies. Homeowners who submit complete, well-prepared applications — typically prepared by an experienced contractor or design-build firm — move through the process substantially faster than those who submit incomplete packages and spend weeks resolving correction comments.
At Animas Valley Construction, our ADU construction process is built around managing the entire project from permit application through final inspection. We help homeowners in Campbell navigate the specific requirements that apply to their lot and their preferred ADU type, so there are no surprises when the permit examiner reviews the submittal. If you’re ready to explore what’s possible on your property, book a free consultation and let’s start with the site-specific questions that matter most.
Frequently Asked Questions
Can Campbell require a minimum lot size to build an ADU?
No. California state law prohibits local agencies from imposing minimum lot size requirements that effectively preclude ADU construction. Most single-family residential lots in Campbell are eligible for at least one ADU and one JADU.
Do I need to replace my garage if I convert it to an ADU in Campbell?
No. State law prohibits Campbell from requiring garage replacement as a condition of approving a garage conversion ADU. You can convert an existing attached or detached garage without building a replacement parking structure.
How long does it take to get an ADU permit in Campbell?
State law requires the city to act on a complete ADU application within 60 days. Submitting a well-prepared, complete application package is the most effective way to minimize delays during plan check.
Are there owner-occupancy requirements for ADUs in Campbell?
California law suspended local owner-occupancy requirements for ADUs through at least 2025. Confirm current requirements with the City of Campbell Community Development Department at the time of your application.
What is the maximum size for a detached ADU in Campbell?
State law establishes a maximum of 1,200 square feet for detached ADUs on single-family lots. Campbell’s local ordinance applies within this framework, and your specific maximum may vary based on lot size and existing primary structure.