How Much Does It Cost to Build an ADU

Golden Heights Remodeling
September 10, 2024

Building an Accessory Dwelling Unit (ADU) is a smart investment, but it’s essential to understand that the cost can vary widely depending on several factors. While the price range for ADUs in Concord, CA, generally falls between $150,000 and $450,000, specific elements of your project will determine where your final costs land. These factors include the size of the ADU, the type of construction (detached, attached, or garage conversion), the quality of materials and finishes, and the complexity of site preparation.

Additionally, labor costs in the Bay Area tend to be higher due to increased demand, and fees for permits, inspections, and utility hookups will also impact the overall budget. Understanding these variables will help you make informed decisions and get the best value for your investment. In this article, we’ll break down the costs for different ADU sizes and layouts, explore permit expenses, and discuss the most budget-friendly options.

How Much Does It Cost to Build a 1000-Square-Foot ADU?

A 1000-square-foot ADU offers ample space for a large one-bedroom or even a two-bedroom unit. The cost for a unit this size can range from $250,000 to $400,000 or more, depending on the finishes, location on the property, and whether it’s a detached or attached unit.

Factors that can influence the cost:

Site preparation: Excavation, leveling, and foundation work will add to the overall cost.
Permits and fees: In California, you’ll need to account for city permits, impact fees, and inspections, which can total up to $20,000 or more.
Materials: Opting for high-end finishes such as hardwood floors or custom cabinets will increase the total cost.
Labor: Professional labor costs in the Bay Area tend to be higher than in other regions due to demand.

How Much Does It Cost to Build an 800-Square-Foot ADU?

An 800-square-foot ADU is a popular size for homeowners who want a balance between cost and functionality. This size unit typically ranges between $200,000 and $320,000. This includes essential construction expenses such as site preparation, utilities, and labor.

Elements impacting costs include:

Utilities: Connecting to existing utilities such as water, electricity, and sewer can add between $10,000 and $30,000.
Design choices: A more basic design with standard fixtures can lower costs, while luxury upgrades will push the price up.
Construction type: Whether you opt for stick-built, prefab, or modular construction will also impact the total price.

How Much Does It Cost to Build a Two-Bedroom ADU?

Two-bedroom ADUs are ideal for creating a separate living space for family or generating rental income. A typical two-bedroom ADU will cost between $250,000 and $450,000, depending on factors such as size and customization. Larger units (closer to 1000 square feet) will be on the higher end of the price range.

Key factors to consider:

Layout: A two-bedroom ADU may require a more complex floor plan, leading to increased design costs.
Appliances and finishes: The inclusion of high-quality appliances and premium finishes can raise the overall budget.
Insulation and energy efficiency: California’s energy efficiency standards will affect construction methods and material choices, particularly for a larger two-bedroom space.

How Much Does an ADU Permit Cost?

Before beginning your ADU project, securing the necessary permits is crucial. The permit costs can vary depending on the size and complexity of the project. Typically, ADU permits range between $5,000 and $15,000. This includes:

Building permits: Required to ensure your ADU complies with local building codes.
Impact fees: These fees can vary but are often reduced or waived for ADUs under 750 square feet, making smaller units more cost-effective.
Inspections: Fees for required inspections during the construction process.

Working with an experienced contractor can help streamline the permitting process and avoid costly delays.

What is the Cheapest Option for an ADU?

If you’re looking to build an ADU on a budget, there are several strategies you can consider to minimize costs:

Garage conversion: One of the most affordable ways to build an ADU is by converting an existing garage. Since the structure is already in place, you’ll save on foundation, framing, and roofing costs. A garage conversion can cost anywhere from $80,000 to $150,000, depending on finishes and utilities.
Prefab or modular ADUs: Prefabricated or modular ADUs can significantly reduce labor costs and construction time. These units are built off-site and assembled on your property, with prices starting at around $100,000 for smaller units.
Small, simple designs: A smaller ADU, especially one under 500 square feet, can be much cheaper. Opting for basic finishes, fewer customizations, and keeping the design simple can help keep costs down to around $100,000 to $150,000.

Types of ADUs and Their Costs

When considering building an ADU (Accessory Dwelling Unit), it’s essential to know that there are various types, each with its own set of benefits and costs. The type of ADU you choose will have a significant impact on your overall budget and construction process. Below, we explore the different ADU types and their associated costs, specifically for projects in Concord, CA.

1. Garage Conversion ADU

A garage conversion is one of the most cost-effective ways to create an ADU because it utilizes the existing structure. There are two main types of garage conversions:

Attached Garage Conversion: Converting a garage that is attached to your home typically costs between $80,000 and $150,000. The costs can vary based on whether the garage already has utilities like electricity and plumbing.
Detached Garage Conversion: Converting a detached garage may cost slightly more, ranging between $90,000 and $160,000, due to additional work needed to connect utilities and possibly reinforce the structure.

2. New Construction Detached ADU

A detached ADU is a standalone structure built from the ground up, separate from the main house. These are more expensive than garage conversions because you’re starting with a new foundation, walls, and roof. Costs for new detached ADUs generally range from $250,000 to $450,000, depending on size, finishes, and site preparation.

3. Second Story ADU (Above-Garage)

Adding an ADU on top of an existing garage creates a second-story unit, which can be an efficient use of space but requires structural reinforcement. This type of ADU is more complex and can cost between $200,000 and $350,000 due to the added expenses of engineering and reinforcing the garage below. It also requires access stairs and sometimes additional parking considerations, which add to the total cost.

4. Attached ADU

An attached ADU is an addition that extends from your existing home but functions as a separate unit. The costs for attached ADUs range from $150,000 to $300,000, depending on the size and level of integration with the existing house. Since attached ADUs share at least one wall with the main house, this can reduce costs compared to a fully detached unit.

5. Junior ADU (JADU)

A Junior ADU is a smaller unit, usually between 200 and 500 square feet, that is created by converting a portion of the existing living space in your home (such as a bedroom or an attached garage). These are the most affordable type of ADU, with costs ranging from $50,000 to $100,000. JADUs are often more cost-effective because they share utilities with the main house and have simpler building requirements.

Final Thoughts

While the cost of building an ADU in CA, can vary widely, careful planning and consultation with an experienced contractor can help you stay within budget. At Golden Heights Remodeling, we provide tailored solutions for ADU construction, ensuring that your project meets your needs and aligns with local regulations. Contact us today for a free consultation on your ADU project!