How Much Does It Cost To Build An Adu

How Much Does It Cost To Build An Adu

Building an Accessory Dwelling Unit (ADU) on a property is becoming increasingly popular. With cities encouraging more ADU construction, homeowners are looking to add these spaces for additional living space or rental income. But many may be wondering, how much does it cost to build an ADU? This article will detail different factors that impact ADU construction and determine how much homeowners can expect to spend when adding an ADU to their property.

What is an ADU?

Before delving into the cost of building an ADU, it’s important to understand what it is. An ADU is an additional residential unit on a single-family lot. It includes a kitchen, a bathroom, and a place to sleep, and it can be a custom-build or a conversion of an existing structure, such as a garage or a basement.

Understanding ADU Construction Costs

When building an ADU, the costs involved vary based on different factors. These factors can be broadly classified into hard and soft costs. The hard costs refer to the direct costs of building an ADU, such as labor and materials. The soft costs are indirect costs, including permits, design work, and architectural fees.

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Factors That Influence Hard Costs

ADU Size and Style

The size and style of an ADU have a significant impact on the total cost of construction. Smaller ADUs tend to be less expensive to construct, while larger ADUs cost more. Similarly, the style of the ADU, such as a detached or attached unit, determines the final cost. Detached ADUs are typically more expensive due to additional site work and utility connections, whereas attached ADUs cut down on these costs.

Site Preparation

Site preparation costs vary depending on the location and the condition of the site. Creating a leveled foundation for the ADU, pouring concrete, and ensuring proper drainage, among other site preparatory work, can add a few thousand dollars to the project’s cost.


The materials used to build an ADU can significantly impact the final cost. Materials such as sustainable hardwood or imported tiles can add to the overall costs. However, compromising on materials can reduce the overall construction cost.


The cost of labor depends on the scope of the project, the workers’ skills and experience, and the location of the construction site. Experienced tradespeople may charge more for their services, adding to the total construction cost.

Factors That Influence Soft Costs

Permit Fees

Permit fees are a crucial aspect of constructing an ADU. Permit fees depend on the location, size, and scope of the ADU project. The permit fees can range from $1,500 to over $5,000.

Architectural and Design Fees

Design and architectural fees depend on the ADU project’s complexity and range from $5,000 to $15,000 or more.

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Utility Connections and Fees

Utility connections such as water, gas, and electricity are significant determinants of the final construction costs. The cost of utility connection and the monthly maintenance fee depends on the local utility providers and the size of the ADU.

How much does it Cost to Build an ADU?

The total cost of building an ADU depends on several factors discussed above. The average cost to build an ADU in the United States falls between $80,000 and $250,000. A smaller and simple one-room ADU may cost between $50,000 to $90,000. A more complex ADU that includes multiple rooms and luxurious finishes is more expensive and can cost up to $350,000.

Frequently Asked Questions

What is the Payback Period for Building an ADU?

The payback period for an ADU can depend on several factors, such as the location and the local rental market. However, the addition of an ADU can pay for itself in five to ten years through additional rental income or added property value.

Can I Rent My ADU?

Renting an ADU is one of the most common reasons for constructing one. Renting the space can help homeowners generate additional income.

Do I Need a Building Permit for My ADU?

Yes, obtaining a building permit is a crucial step in the ADU construction process and required by most cities and counties.

How Long Does it Take to Build an ADU?

The construction of an ADU usually takes three to five months. However, the exact timeframe depends on factors such as the ADU size, complexity of the project, and weather conditions.

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Building an Accessory Dwelling Unit provides homeowners with additional living space, rental income, and added property value. The cost of constructing an ADU depends on several factors such as size, construction materials, labor, permits, and architectural fees, among others. While the total cost of ADU construction may seem daunting, it can be a valuable investment for homeowners and provide economic benefits in the long term.

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