What is an ADU? – ADU Definition and Meaning to California Homeowners
What is an accessory dwelling unit (ADU) according to the law in California?
Let’s break it down into a very simple legal definition, and explain how it will dramatically change your cost of living over the next 10 years.
And then we’ll go into all the different things ADUs can do for you based on that definition/meaning.
What is an ADU (Accessory Dwelling Unit)
Video explaining: “What is an ADU?”
Dwelling Unit = Permanent Home
A dwelling unit is a wordy way to say home. It’s a place where a person can permanently live.
Accessory = Secondary, Extra (not primary)
Accessory basically means secondary, extra, or auxiliary.
If you’ve got a lot with a house on it, that house is the primary dwelling unit.
When you go to build a second permanent home, that’s an accessory dwelling unit.
It doesn’t have to be a house
Notice I keep saying “home” and not “house” - that’s because an ADU doesn’t have to be a literal house.
For example, if you’ve got a house with a space like a garage or a basement that you don’t use… you can convert that space into a home with its own entrance and amenities. And that’s an ADU.
But it does have to be permanent
An ADU needs to be a place where a person can permanently live.
The state of California defines this in its health code in a few important ways:
ADUs have a permanent foundation
ADUs need a way to cook - that’s a stove hookup
ADUs need a way to clean up - that’s a sink hookup
“(1) ‘Accessory dwelling unit’ means an attached or a detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a proposed or existing primary residence. It shall include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel as the single-family or multifamily dwelling is or will be situated. An accessory dwelling unit also includes the following:
(A) An efficiency unit, as defined in Section 17958.1 of the Health and Safety Code.
(B) A manufactured home, as defined in Section 18007 of the Health and Safety Code.”
The law explicitly says that they can prefabricated and they can be efficiency units.
But if you’ve got a tiny house on wheels without a city-approved stove hookup and plumbing… that’s not an ADU. It’s cool! But it’s not an accessory dwelling unit.
Note: since this article was originally published, several jurisdictions have written Movable Tiny Homes or Tiny Homes on Wheels (THOWs) into their ADU ordinances. These are often less permanent, so the definition is expanding in these more permissive jurisdictions!
They can be pretty big!
New detached Accessory Dwelling Units can be 1200 square feet (that’s big!)
And if you’re converting an existing structure, they can be as big as the existing structure, even if that’s a 3,000 square foot barn!
Some of the cities that encouraged ADU construction early (like Portland) had stricter size restrictions so a lot of people think that ADUs have to be smaller. But that’s not the case down in 2020 in California.
And in the early days of California ADUs, a lot of cities passed restrictive ordinances that kept people to building ADUs that were smaller than the primary house and could only cover a certain percentage of their lot. But all that’s out the window thanks to the suite of new California state laws that came into effect in 2020.
California’s state government has now said ADUs can be up to 1200 square feet.
Cities are allowed to pass ordinances to restrict this a bit, but the restrictions are limited by the state law. Not a lot of cities got ordinances in place in time for 2020 so the vast majority of home owners are eligible to build 1200 sq. ft. units.
Why do Accessory Dwelling Units matter to you?
Accessory Dwelling Units matter to all Californians, and perhaps all Americans.
Here’s a video of the dozens of different ways people use ADUs, the many different structures that can be built with ADU permits, and the many motivations people have.
Homeowners can make money with ADUs
If you own a property in California, you can now build an ADU and rent it out to generate income.
If you don’t know about ADUs, you are unintentionally missing out on a passive income stream. That’s because almost all homeowners in the state now have the ability to build not one but TWO ADUs.
And it matters to everybody else too
If you rent, ADUs are going to dramatically change your cost of living once they gain traction.
Cities with wide adoption of Accessory Dwelling Units have shown us that ADU rentals are usually priced more affordably than similarly sized rental units in big apartment buildings or primary home rentals. The two big examples here are Portland and Vancouver.
The reason for that is usually attributed to some of the positive traits of ADUs. They’re cheaper to build per square foot than big apartment buildings (which I think this is the biggest reason they tend to be more affordable per sq. ft.)
The other thing that ADUs will do is they will increase the supply of housing in California.
The meaning of ADU is very versatile - it can include a detached new construction or the conversion of a 2 car garage like this San Francisco ADU by Inspired ADUs
For the longest time, local agencies have blocked the construction of new home developments in California. The very generous ADU laws are pretty much the end of single family zoning in California. You can preserve that setup if you want, but you’re zoned for multi-family if you want.
And that’s going to allow for more inventory. When supply goes up, price comes down.
When ADUs gain traction, they’re going to lower housing costs for everybody.
Accessory Dwelling Units could solve the housing shortage
How To ADU exists to solve the housing shortage. We want to accelerate the construction of ADUs by empowering homeowners to build their wealth and their community.
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