Costs to Design and Build ADUs in California
An accessory dwelling unit can be a deeply personal thing. Every property, home, and homeowner is different and your needs, tastes, and site will be different from those of your neighbor. So naturally, design, permitting, and construction costs will vary from project to project.
In the Bay Area, you can expect a 650-square-foot ADU to cost around $350,000 on average to construct where a 350-square-foot ADU will likely cost around $225,000 to build. Of course, your costs may be more or less, depending on what you want for your accessory dwelling. Although these are much less than the cost of building a full custom home, it is still a significant investment for most families.
Let’s get a little more specific. Although your experience will be unique, you can get an idea of what it will cost by looking at similar projects. Here’s a look at some real costs for accessory dwellings in the Bay Area.
A 650-square-foot accessory dwelling in El Cerrito cost $290,323 to design and build. It has one bedroom, one bathroom, a kitchen/living area, and a loft.
A one-bedroom, one-bathroom ADU in Santa Cruz cost $345,195 to design and build. It’s attached to a garage, which is shared with the main home.
A cottage in Berkeley cost $310,276.00 to design and build. It has two bedrooms, a bathroom, a kitchen, and a living area.
A 374-square-foot, versatile space in Concord, CA, can be used for anything the homeowner wants. It includes a living area, a bathroom, a kitchen, and storage cabinets. The total cost was $248,668.24
A larger ADU on a sloping site is currently being built in Oakland with an estimated all-in cost of $510,000.
If you’re adding an accessory dwelling to your home in the San Francisco Bay Area, expect to spend between $225,000 and $500,000 for design, permitting, and construction. Below are some additional costs for ADU projects in cities around the San Francisco Bay Area.
Cost to design and build a backyard accessory dwelling in Mountain View, California
A New Avenue client in Mountain View, CA wanted to build a multi-purpose accessory dwelling unit. At first, it would serve as a home for her daughter, who had recently graduated from college. Later, it could be a comfortable place for an older adult.
The total budget for this gorgeous one-room studio with half bath was 254,938.88.
Cost to design a one-bedroom attached ADU in Berkeley
A Berkeley homeowner came to New Avenue looking for plans to demolish her detached garage and build an accessory dwelling.
New Avenue’s designer created an attached ADU that will be comfortable for family and for renters. Now the homeowner will have a place for her mother to live right next door. When she’s not using it for family, she can rent it out.
The design budget for this project is $15,400. Consultants are estimated to be $8,000 with estimated permit fees at $6,000. The estimated construction cost is projected to be around $250,000.
Cost to convert a basement to an apartment in Berkeley, CA
Berkeley homeowner Johanna came to New Avenue for a basement ADU. She wanted a place for her mother-in-law to live comfortably.
New Avenue created custom plans to expand the basement and convert it into an ADU. The new apartment features a bedroom, a bathroom, a laundry area, a kitchen/living area, and plenty of storage space. The basement ADU features a kitchen/living area, a bedroom/office, a bathroom, and a storage/laundry area.
The cost to design and permit this project was $44,360. The estimated construction budget is $387,000.
Cost to design and build an art studio/accessory dwelling unit in Berkeley
Berkeley homeowners Michael and Lisa wanted an accessory dwelling that could also be an art studio. New Avenue designer Matt Waitkus delivered, creating a design that made efficient use of the space while keeping everything comfortable, open, and bright. The design includes a loft (accessible by a rolling ships ladder), a kitchen, a bathroom, washer/dryer connections, and a living area. The lighting is perfect for an art studio, and the homeowners will be able to use this as a home for family or renters as needed.
The cost to design, permit, and build this ADU was $356,040.00.
Cost to Convert a Two-Car Garage to a 400-square-foot ADU in Berkeley
Shannon, a homeowner in Berkeley, wanted to convert her old garage into an accessory dwelling that could be used by anyone: herself, her family, her guests, and, in the future, tenants. She needed a place that would be great for work and everyday life.
A New Avenue designer put together a design that could be used for just about anything. The design keeps the garage’s existing roof and skylights while completely recreating the interior.
The cost to design and build this project was $227,750.
(cost updated to reflect 2020 prices)