- ADU Guide for Homeowners
Accessory Dwelling Units (ADUs) in California
An Accessory Dwelling Unit, commonly called an ADU, is an additional residential unit located on the same property as a primary home. California homeowners use ADUs to create housing for family members, generate potential long-term rental income, add private guest space, or make better use of an existing property.
Although California law supports ADU development, the type, size, location, design, and approval pathway available for a specific project depend on the property, permit jurisdiction, existing buildings, setbacks, utilities, site access, and other local requirements.
Interior view of a modern California accessory dwelling unit
What Is an Accessory Dwelling Unit?
An Accessory Dwelling Unit is a secondary residential unit located on the same lot as an existing or proposed primary dwelling.
Depending on the property and proposed project, an ADU may be:
- A new detached structure
- An addition connected to the primary home
- A converted garage or accessory structure
- A unit created from qualifying space inside a home
- A smaller Junior ADU within a single-family residence
A standard ADU generally includes independent living, sleeping, cooking, and sanitation facilities. A Junior ADU is smaller and follows a different set of requirements.
Why California Homeowners Build ADUs
An ADU can support several homeowner goals:
- Create private housing for parents or relatives
- Provide space for adult children
- Develop a potential long-term rental unit
- Add a guest house or flexible living space
- Create space for a caregiver
- Make better use of an existing garage
- Increase the practical utility of the property
- Plan for changing household needs
The right approach depends on the property and the homeowner’s intended use. A rental-focused ADU may need a different layout, privacy plan, parking arrangement, and utility strategy than a unit designed for an aging parent.
Rental income, property-value growth, and investment returns are not guaranteed and should be evaluated using current local information and conservative assumptions.
Design-Build ADU Services
Team All Star Construction provides design-build ADU services, coordinating:
- Feasibility review
- Design and permitting steps
- Construction and final inspection
This integrated approach allows ADU projects to move forward with a defined scope, realistic timelines, and fewer surprises caused by jurisdiction-specific requirements.
Types of ADUs in California
Detached ADU
A detached ADU is a separate residential structure located on the same property as the primary home. It can offer greater privacy and layout flexibility but requires a new foundation, building envelope, utility connections, and complete residential systems.
Garage Conversion ADU
A garage conversion transforms an existing garage into residential living space. Reusing the structure may be practical, but the slab, foundation, framing, roof, ceiling height, moisture protection, fire separation, utilities, and previous alterations must be evaluated before assuming that conversion is the least expensive option.
Junior ADU (JADU)
A Junior ADU, or JADU, is a smaller residential unit created within the walls of a proposed or existing single-family residence. JADUs are generally limited in size and follow separate requirements for kitchens, sanitation facilities, access, and owner occupancy.
Attached ADU
An attached ADU is connected to the primary residence, often through a new addition or the reconfiguration and expansion of existing space. The design must account for the existing home, structural connections, access, privacy, and applicable size and setback requirements.
Which ADU Type May Be Right for You?
The most appropriate ADU type depends on several practical questions:
- Is there enough usable yard area for detached construction?
- Does the property contain a garage worth evaluating?
- Can existing interior space be reconfigured?
- How much privacy is needed?
- What size and bedroom count support the intended use?
- Where are the sewer, water, electrical, and gas connections?
- Is construction access available?
- Are there slopes, easements, fire conditions, or drainage issues?
- What project budget is realistic?
- Will the unit be used by family members or as a long-term rental?
A floor plan should not be selected in isolation. It should be evaluated against the property, local requirements, utility routes, homeowner goals, and construction budget.
Not Sure What Type of ADU Fits Your Property?
A detached unit, garage conversion, attached addition, or Junior ADU may each work differently on the same property. Before selecting a floor plan or estimating a construction budget, start by reviewing the property address and basic site conditions.
Start with a free online site check. Enter your address to get an early look at what kind of ADU may be possible on your property.
How the ADU Planning and Build Process Works
A complete ADU project normally progresses through several connected stages:
- Property and jurisdiction research
- Preliminary feasibility review
- ADU type and size selection
- Budget and financing planning
- Concept design
- Architectural and engineering preparation
- Permit submittal and plan check
- Corrections and agency clearances
- Pre-construction planning
- Construction and required inspections
- Final corrections and completion
The exact sequence and timing can vary by city, project type, utility requirements, site conditions, design complexity, engineering needs, and agency review.
ADU Costs in California
ADU cost depends on more than square footage. Major cost factors may include:
- ADU type and size
- Existing structure conditions
- Foundation and structural work
- Architectural design and engineering
- Surveying or soils work when required
- Permit review and agency fees
- Sewer, water, electrical, and gas work
- Site access and material staging
- Grading, drainage, or retaining walls
- Fire and energy-code requirements
- Interior and exterior finish selections
- Construction scope and market conditions
Online prices should be treated as early planning information—not as a bid or guaranteed final cost.
Estimate Your ADU Cost in Seconds
Use our quick ADU cost calculator to get a planning estimate based on your project size and monthly payment option. Start with your square footage, choose a payment term, and see an estimated project cost before requesting a free feasibility review.
Estimates are for planning purposes only. Final pricing may vary based on design, permits, site conditions, engineering, utilities, finishes, and project scope.
ADU Permits and Local Requirements
California establishes statewide ADU requirements, but cities and counties still review projects for applicable zoning, building, fire, utility, energy, and safety standards.
A typical permit process may involve:
- Confirming the correct permit jurisdiction
- Preparing architectural plans
- Completing structural and energy documentation
- Submitting the application
- Responding to plan-check comments
- Obtaining utility or fire clearances when required
- Paying applicable fees
- Completing construction inspections
- Receiving final approval
The existence of a statewide ADU pathway does not mean that every plan is automatically approved for every property.
ADU Financing Options
Homeowners may explore several ways to fund an ADU, depending on available equity, credit, project stage, loan qualifications, and repayment goals.
Potential options may include:
- Cash
- Home-equity line of credit
- Home-equity loan
- Cash-out refinance
- Construction-related financing
- Renovation financing
- Other third-party loan programs
Team All Star Construction is not a lender. Rates, terms, approvals, monthly payments, and loan conditions are determined by third-party financing providers.
Complimentary
Start With a Professional ADU Feasibility Report
An ADU should begin with the property—not with a generic floor plan, verbal estimate, or assumed construction budget. For qualified homeowners, the Professional ADU Feasibility Report provides a property-specific starting point before major design, engineering, permit, or construction expenses begin. Depending on the property and available information, the report may include:
- Maximum ADU Size
- Setbacks
- Buildable Area
- Zoning Review
- Estimated Budget
- Rental Income Potential
- Site Constraints
- Preliminary Build Concept
- Next Steps
Most homeowners spend hundreds or even thousands on planning before knowing what can actually be built. Our Professional ADU Feasibility Report helps you understand your property’s potential before making that investment.
Accessory Dwelling Unit FAQs
What is the difference between an ADU and a JADU?
A standard ADU is generally a complete independent residential unit. A JADU is smaller, must be created within a proposed or existing single-family residence, and follows separate requirements for size, kitchens, sanitation facilities, access, and owner occupancy.
Do I need architectural plans before checking whether an ADU may work?
No. Property and feasibility research should come first. This early review helps identify the permit jurisdiction, likely ADU pathways, practical building area, utilities, site constraints, and questions that should be resolved before a full plan set is prepared.
Are ADUs allowed everywhere in California?
California law requires local jurisdictions to allow qualifying ADUs, but every property still needs to comply with the applicable state and local requirements. Zoning, existing structures, setbacks, access, utilities, fire conditions, and site constraints can affect the available design.
How large can an ADU be?
The allowable size depends on the ADU type, bedroom count, local standards, state-protected pathways, existing dwelling, and property conditions. A citywide maximum does not guarantee that the same size can be placed practically on every lot.
Is a garage conversion always less expensive than a detached ADU?
No. A garage conversion can reuse an existing structure, but significant foundation, framing, roofing, moisture, fire-safety, utility, or code work may still be required. The existing garage must be evaluated before comparing costs.
Can I rent out an ADU?
ADUs are often used as long-term rental housing, but rental rules can vary by jurisdiction and may restrict short-term use. Potential rent depends on the neighborhood, unit size, condition, amenities, privacy, parking, utilities, and market conditions.
How long does an ADU take?
The overall timeline depends on property research, design, engineering, permit review, agency clearances, corrections, site preparation, construction complexity, inspections, material selections, and homeowner decisions. A property-specific schedule should be developed after the project scope is better defined.
What should I do first?
Begin with the property address and homeowner goals. From there, the permit jurisdiction, possible ADU type, approximate size, site constraints, utility considerations, and planning risks can be reviewed before major design or construction expenses begin.
ADU feasibility, costs, timelines, financing, rental income, property-value effects, permit requirements, and approval outcomes vary by property, jurisdiction, site conditions, project scope, agency requirements, selected finishes, and third-party review.
Team All Star Construction ADU Builder is operated by Team All Star Construction, CSLB #1009760.