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ADU Construction Costs: How Much Does It Cost to Build an ADU in California? [2025 Guide]

Accessory dwelling units, or ADUs, are one of the most popular ways for California homeowners to add extra living space, generate rental income, or support multigenerational living. But in 2025, with inflation and changing regulations, understanding ADU construction costs is more important than ever. Whether you’re considering a garage conversion ADU, a detached ADU in your backyard, or an attached ADU addition, knowing the full picture of construction costs, including soft costs, labor costs, and additional costs, will help you make smarter decisions for your project.

At Golden State ADUs, we specialize in full-service ADU design and construction throughout Northern California. We’ve helped hundreds of property owners turn their vision into reality. In this comprehensive guide, we’ll break down current ADU costs, what drives them, and how to control your project’s cost from start to finish.

Average ADU Construction Costs in California

Total Cost Ranges

The cost to build an accessory dwelling unit ADU in California can vary widely based on size, location, and type. In 2025, the total cost typically ranges from $100,000 to over $400,000. The typical range depends on whether you’re building a garage conversion ADU, a detached ADU, or an attached ADU. Here’s what most property owners are seeing today:

• Garage Conversion ADU: $100,000 – $180,000
• Attached ADU: $175,000 – $300,000
• Detached ADU: $225,000 – $450,000
• Prefab or Modular ADUs: $150,000 – $250,000

Each type of ADU project comes with its own set of costs related to permitting, materials, and utilities. For example, a garage ADU often leverages the existing structure and existing utilities, which can significantly reduce site preparation and foundation costs. Detached ADUs, while offering privacy and flexibility, tend to be more expensive due to standalone construction.

Cost Per Square Foot in 2025

ADU construction costs are usually expressed per square foot. In 2025, here are the most accurate figures available:

• Low-end construction: $200 – $275 per square foot
• Mid-range builds: $300 – $400 per square foot
• High-end custom ADUs: $450 – $600 per square foot

Smaller units tend to have a higher cost per square foot because soft costs and infrastructure are spread across fewer square feet. For instance, the overall cost of building a 400-square-foot ADU might approach that of a 600-square-foot model, due to fixed permitting and design fees.

Key Factors That Influence ADU Costs

Every ADU project is unique. Your overall cost can change significantly depending on a few key factors:

Type of ADU

• Garage conversion ADUs generally offer the lower cost path to building an ADU, since the structure already exists.
• Attached ADUs require new framing but often share systems with the main house, which can reduce some utility-related expenses.
• Detached ADUs are the most expensive due to foundation work, utility trenching, and standalone systems.

ADU Size and Design Complexity

Larger units typically cost more in total cost, but not always in cost per square foot. A highly detailed, small-footprint ADU with custom cabinetry and high-end fixtures can cost more than a standard larger unit. More complex layouts, vaulted ceilings, or multi-room designs increase construction costs.

Site Preparation and Conditions

The cost of site preparation can add $10,000 to $40,000 to your project’s cost. If your site is sloped, has limited access, or poor soil quality, you’ll need additional grading or foundation work. Connecting utilities also becomes more expensive with poor site access or long distances between the ADU and existing service lines.

Permitting Costs, Building Permits, and Impact Fees

Permitting costs in California vary widely based on city and county. Some local governments charge less than $5,000 in fees, while others exceed $20,000 in building permits and associated fees. Fortunately, California law waives impact fees for ADUs under 750 square feet. Still, other soft costs, like energy compliance (Title 24), engineering, and city review fees, can add up.

At Golden State ADUs, we streamline permitting for all our clients and ensure compliance with local building codes, zoning laws, and local codes from day one.

Location and High Cost Areas

ADU construction costs also vary based on location. High cost areas in California, such as parts of the Bay Area and Los Angeles, typically see higher labor costs, permitting fees, and material prices. These regional differences can significantly impact your total cost and should be considered when budgeting.

Breaking Down ADU Construction Costs

Let’s take a closer look at what makes up the cost to build an ADU:

Soft Costs

Soft costs cover all pre-construction and non-physical expenses, including:

• Design costs and architecture: $8,000 – $20,000
• Engineering and energy reports: $3,000 – $7,000
• Permitting costs and building permits: $4,000 – $15,000
• Project management and site surveys: $1,500 – $5,000

Total soft costs can account for 15% to 25% of your overall cost, depending on project scope and local regulations.

Hard Construction Costs

Hard costs refer to the physical construction work, which typically includes:

• Foundation and framing
• Roofing, siding, windows, and doors
• Plumbing, HVAC, and electrical systems
• Insulation and drywall
• Interior finishes like flooring, cabinetry, and lighting

The higher the finish level, the higher your adu construction costs. For instance, hardwood flooring and quartz countertops will cost more than vinyl plank and laminate options.

Labor Costs

Labor costs are rising across California, contributing to the increasing cost of building an ADU. Unionized labor or prevailing wage rules in some cities can push prices up by 10% or more. In 2025, labor shortages are still impacting project timelines and availability, particularly in high-demand markets.

Utility Connections

New or upgraded water, sewer, gas, and electric connections can cost anywhere from $10,000 to $35,000. Detached ADUs often require trenching to connect back to the main house, which adds to the project’s cost. Some cities are facing delays with utility companies like PG&E, which can lead to additional scheduling and additional costs.

What You Get at Each Budget Level

Under $200,000

This range typically includes garage conversion ADUs, small prefab units, or basic attached ADUs built within existing space. These ADUs may have:

• Modest finishes
• Shared utility lines
• Compact layouts

$200,000 – $300,000

This range covers most attached ADUs or modest detached ADUs (around 500–700 sq ft). These units typically feature:

• Private kitchens and baths
• Mid-level finishes
• Energy-efficient systems

Over $300,000

High-end detached ADUs with large footprints and luxury features, such as vaulted ceilings or solar panels, tend to fall in this range. These units often qualify as granny flats or long-term rental income properties and include:

• Custom cabinetry and premium appliances
• Separate metering for utilities
• Dedicated entrances and outdoor patios

ADU Financing in 2025

Common Financing Options

To fund your ADU project, many property owners use:

• Home equity loans or HELOCs
• Cash-out refinancing
• Construction loans through local banks
• Specialty ADU financing providers

At Golden State ADUs, we work with financing partners to help you find cost effective solutions based on your goals and property.

Local Grants and Incentives

In previous years, the CalHFA ADU Grant offered up to $40,000 for eligible homeowners to cover soft costs. While the future of this program is uncertain, some local governments are considering extensions or alternatives in 2025. Our team monitors all funding opportunities and will help you apply for any available incentives.

Learn more in our guide: How to Finance Your ADU in California

How to Control ADU Construction Costs

Start with a Full-Service Design-Build Team

Working with Golden State ADUs means every step of your ADU project is coordinated, from design and permitting to construction costs and finishing. A well-integrated team avoids delays and change orders that increase your project’s cost.

Plan Ahead and Build Smart

Get permits early, confirm your design before construction begins, and explore cost effective materials. Our team offers value engineering strategies to reduce expenses without compromising on quality.

Consider Existing Structures

If you have an existing garage, converting it to a garage ADU can cut your total cost by leveraging the existing structure. Similarly, using existing space like basements or attic areas can also save money while adding additional square footage.

Property Management Considerations

Once your ADU is complete, managing it effectively is key to maximizing rental income and maintaining your property’s value. Many property owners hire professional property management services to handle tenant relations, maintenance, and compliance with local regulations, which can vary based on your location and the type of ADU.

Real ADU Cost Examples from Northern California

Sacramento

• Garage conversion ADU (450 sq ft): $175,000
• Detached ADU (600 sq ft): $260,000 – $290,000
• Popular among homeowners looking to generate rental income or house family members

Elk Grove and Roseville

• Attached ADU (700 sq ft): $240,000 – $280,000
• Detached ADUs up to 900 sq ft typically run between $290,000 and $350,000
• Commonly used for aging parents or rental units to create steady income

View our portfolio of completed ADUs

Why Work with Golden State ADUs

Transparent Pricing and Local Knowledge

We understand local building codes, zoning laws, and local codes across Sacramento and surrounding areas. Our pricing is clear, detailed, and designed to help you understand every line item in your ADU pricing.

Trusted by California Property Owners

We’ve completed over 100 successful ADU projects in Northern California, each designed with quality, livability, and property’s value in mind. Whether you’re building an ADU for aging parents, renters, or your own office, we ensure your project meets your needs and local requirements.

Ready to get started? Schedule your free consultation today

Frequently Asked ADU Construction Costs Questions

How much does it cost to build an ADU in California in 2025?

Most ADUs cost between $200,000 and $350,000, though garage ADUs and conversions can be completed for less. Detached ADUs and high-end builds may exceed $400,000.

What is the cost per square foot for an ADU in 2025?

Expect between $250 and $450 per square foot, depending on size, materials, and complexity.

Does building an ADU increase my property’s value?

Yes. An ADU can raise your property’s value by 20% or more, especially if it offers rental income potential.

Are ADUs a good investment in today’s real estate market?

Yes. As California’s real estate market remains competitive, building an ADU is a good investment that adds living space, equity, and steady income.

What are the biggest hidden costs when building an ADU?

Often, site preparation, utility connections, and design costs surprise homeowners. Working with a seasoned builder helps anticipate these additional costs.

Final Thoughts

Building an ADU in California is one of the most impactful ways to add value, flexibility, and income to your existing property. In 2025, expect a total cost between $200,000 and $350,000, depending on the size, type, and project complexity. By understanding your options and working with an expert team like Golden State ADUs, you can stay in control of your construction costs while creating lasting value for your family and your future.

Contact Golden State ADUs to get your personalized cost estimate and project plan today. Book a Free Consultation