In California, thanks to a number of state-level interventions in recent years, building an accessory dwelling unit, or ADU, is easier than ever.

Still, construction projects, even of a tiny home, are a major undertaking for the average homeowner. Before lining up contractors and breaking ground, a property owner might spend thousands of dollars and wait weeks just to get architectural plans drafted and approved by a local permitting agency.

Now, though, California is trying to reduce those up-front barriers as part of a broader push to address its housing crisis.

In an effort to make it easier and cheaper for homeowners to build backyard units, a state law passed in 2023 requires local governments to provide homeowners with a slate of pre-approved ADU plans from which they can choose. The homes, sometimes called granny flats, appeal to some families looking for multigenerational housing, while other owners use them as an investment opportunity.

Under the law, AB 1332, which went into effect this year, homeowners choosing a pre-approved plan must have their permits approved in 30 days or less. The typical timeline to get ADU permits approved is 60 to 90 days.

“Reducing costs, reducing confusion, reducing delays — all of that goes a long way to help everyday homeowners who are trying to build new housing,” said Jonathan Pacheco Bell, vice president of policy and programs with the Casita Coalition, an ADU advocacy group.

Homeowners must still pay the architectural firm that drafted the plans a fee for the right to use them — but the costs range from $1,000 to $7,000, which is far below the typical cost of custom plans, which can run between $5,000 and $15,000, said Samantha Dolgoff, who manages ADU permitting for a number of cities in Santa Clara County.

“That’s a huge thing — especially for homeowners who might not have a lot of money and want to save as much as they can for construction costs,” Dolgoff said in an interview.

Construction of an ADU typically ranges from $500 to $600 per square foot, so a small 600-foot, one-bedroom ADU might cost $300,000. Hookup costs for water and electricity add around $15,000 to the total cost. Preparing the foundation of a site can itself cost around $100,000 for an ADU-sized parcel.

The recent law is just one of many ways the state of California is trying to empower residents to build more ADUs, sometimes in the face of local opposition.

Homeowners are responding — last year, one in every five of the 125,228 new housing units built in California was an ADU.

Some cities are making it particularly easy for homeowners to consider their options.

“For someone who’s not versed in construction, even just getting started and finding an architect can be a big hurdle,” said Christian Murdock, community development director for Mountain View. “This lowers one of those hurdles.”

Of course, even a heavily subsidized set of blueprints doesn’t eliminate all the headaches. Homeowners still need to produce a site plan — a map showing where the ADU will go and how it connects to utilities like water lines and power. Some architects or pre-manufactured ADU companies bundle this service into their offerings. Others charge extra.

Homeowners should be cautious of any ]initial price estimates they see attached to pre-approved plans, said Sara Dean, principal at IF/THEN Studios, which has a number of pre-approved ADU options.

“California is complicated,” she said. “We have many different seismic zones and soil types, all of which require different structural work. Ask lots of questions to the company selling plans, and if you get answers that are too simple, be wary of that. … ADUs have all the complexity of design and permitting that a home does, but without the square footage.”

Still, in many of the California’s most expensive communities, where the housing stock is composed of mansions and large-lot homes, an ADU might be one of the only affordable options available to renters.

In Los Altos, for example, the median home sold is 2,600 square feet and costs $4.9 million, according to data from MLSListings. Even a modest two-bedroom home rents for upward of $4,500 a month.

For software engineer Aditi Nagaraj, 36, those prices put the community where she grew up out of reach. But when her father in 2020 decided to build a two-bedroom ADU in the backyard of her childhood home, Nagaraj and her husband, Casey Davis, 37, moved in, seizing the chance to raise their two children, ages 2 and 4, near family. They pay Nagaraj’s parents $4,000 a month in rent.

“It’s such a rare opportunity to be in this area at this price,” Nagaraj said.

Nagaraj’s sister, who lives with her parents in the main home, routinely stops by for breakfast. Nagaraj and Davis bring their kids to the main house for dinner a few times a week.

“It’s community living,” Nagaraj said. “We’re all caretakers of the whole space, and we’re looking out for each other.”

Some cities are offering residents more than just plans. In South San Francisco, unincorporated Alameda County and Marin County, homeowners can also access free building and design support via a partnership with the nonprofit HelloADU.