Accessory Dwelling Units, or ADUs, are one of the most popular ways to find housing in California and other places. As home prices go up and the need for affordable housing grows, more homeowners are asking, "What is an ADU, how much does it cost, and is it really worth building one?"
We'll explain everything you need to know about ADUs in this blog, from what they are and what kinds there are to their costs, plans, benefits, and even problems. This guide will help you whether you want to build one yourself or just want to learn more about the trend.
What does ADU stand for?
An Accessory Dwelling Unit (ADU) is a small, separate home that is built on the same lot as a main house. As a "second home" on your property, think of it.
HUD says that an ADU must have its own kitchen, bathroom, and place to sleep. You can rent these units out, use them for family members, or even turn them into a private office or guest house.
👉 Find out more about what ADU means on our website.
Different kinds of ADUs
There are different kinds of ADUs, and the best one for you depends on the size of your property, your budget, and what you want to do with it:
- Detached ADU – A standalone unit, also known as a "backyard home."👉 Look at our Detached ADU choices.
- ADU that is attached – It was built as an addition to the main house and shares a wall with it.
- Garage Conversion ADU – Making a garage into a place to live.
- Basement ADU – A finished basement with its own door and utilities..
- Above-Garage ADU – Putting a small house on top of a garage.
There are different costs and benefits for each type, but they all add value and flexibility to your property.
What is the price of an ADU?
Prices can be very different, but in California, they usually fall within this range:
- Garage Conversion ADU: Between $80,000 and $150,000
- Attached ADU: $120,000 to $250,000
- Detached ADU: $150,000 to $400,000 or more
The size, design, permits, and materials all affect the cost.
Check out Zillow's housing data to see why ADUs are a cheaper option than buying a whole new house. To plan your budget, look at our ADU cost breakdown.
Plans for Accessory Dwelling Units
ADU plans can be anywhere from 400 to 1,200 square feet and come in a variety of sizes and layouts. Most plans have a bedroom, a bathroom, a small kitchen, and a living room.
Some homeowners choose custom designs, while others choose pre-approved ADU plans to save time and money. Plans that have already been approved by the city are often easier to get through. Look at our plans and designs for ADUs for ideas.
Benefits of ADUs
ADUs are more than just extra space. The main benefits are:
- Rental Income – You can rent out your ADU and make money every month.
- Family Housing – Make room for older parents, adult children, or guests.
- Raise the Value of Your Property: – Homes with ADUs usually sell for more (Redfin says).
- Affordable Housing Solution – Help California get out of its housing crisis.
- Flexibility – You can use it as a home office, gym, or creative studio.
👉 Check out our guide on how ADUs can help homeowners.
Problems with ADUs
ADUs are great, but they also have some problems:
- Upfront Costs – Even with financing, building isn't cheap.
- Permits and Zoning – Rules are different in each city, which can slow down projects.
- Property Taxes – In California, your tax bill might go up a little bit if you make improvements.
ADU that is not attached vs. ADU that is attached
One of the most common questions homeowners have is, "What's the difference between attached and detached ADUs?"
- Detached ADU – A separate home that offers more privacy.
- Attached ADU – This type of ADU is connected to the main house and is usually cheaper to build.
👉 Visit our site to find out more about detached ADUs.
California ADU Rules for 2025
California has been making it easier to build ADUs by passing laws. In 2025, there will be new updates, such as:
- Most cities will be able to approve permits faster.
- Parking rules for ADUs near transit are less strict.
- Incentives for ADUs that are affordable housing.
These changes are meant to help with the state's lack of housing.
👉 Check out our ADU laws blog to stay up to date.
FAQ: Common Questions About ADUs
What is a unit for an accessory dwelling?
An ADU is a small, separate living space built on the same lot as a main house.
What is the price of an ADU?
Depending on the type, size, and materials, costs can be anywhere from $80,000 to $400,000 or more.
What are the pros of ADUs?
They make the property worth more, make space for family, and bring in rental income.
In California, will an ADU raise property taxes?
Yes, but not by much. The taxes are based on the value of the new construction, not the whole house.
What is the difference between ADUs that are attached and those that are not?
Attached units are next to the main house, while detached ADUs are their own separate buildings.
Final Thoughts
ADUs aren't just a passing fad; they're a long-term answer to housing problems in California and the rest of the U.S. Building an ADU is one of the best things you can do in 2025 if you want to make more money, find a place for your family to live, or raise the value of your property. Are you ready to start your project? For expert help with planning, permits, and designs that save you money, go to Fortune ADU.
