All ADU Resources

What is an ADU (Accessory Dwelling Unit)?

Accessory Dwelling Units have exploded in popularity in the past few years. So what are ADUs and are they right for me?

April 9, 2021

Ever since the passage of California Assembly Bill 68 (AB 68) in October 2019 that encouraged the construction of Accessory Dwelling Units, ADUs have flourished. In 2019 alone, almost 16,000 ADU permits were issued across the state, up from just 6,000 the year prior. So what exactly is an ADU, and is it right for you?

What is an ADU?

Also known as granny flats, in-law units, backyard cottages, secondary units, carriage homes, and tiny homes, accessory structures have emerged as a significant piece of the affordable housing puzzle across the state of California as well as a few other states across the country. The California Department of Housing and Community Development calls ADUs an "innovative, affordable, and effective option for adding much-needed housing in California."

ADUs are separate livable units that are on the same property as a primary residence, whether a single-family home or a multi-family home. Most ADUs in California take the shape of a backyard cottage, but can also be attached to the main house or even converted space such as an extra bedroom, storage rooms, a basement apartment, an attic, or a garage.

ADUs can be detached accessory apartments (detached ADU), a junior accessory dwelling unit (junior ADU or JADU), an interior ADU or conversion, or an attached ADU that connects to the main residence.

Check out our post on the different types of ADUs for more details.

Because ADUs are independent living spaces, they usually are also built to the quality of a small primary home - with their own robust foundation, utilities connections, exterior access, and living area. Importantly, ADUs ordinances require the space to have separate sanitation facilities and a small kitchen to qualify as a separate livable space.

Whether you're a homeowner looking for a cost-effective way to develop more family living space, an empty-nested retiree looking to downsize without selling your existing home, or a property investor looking for new rental apartments, ADUs provide the flexibility to build room for more independent living space.

Why are ADUs showing up everywhere?

California's 2019 AB 68 legislation removed many of the setbacks that previously stood in the way of the ADU building process. Before the law, cities and counties could take up to four months to even review your application to build your in-law unit; but the new legislation has cut down that time in half, requiring that local governments across the state must review your ADU application within 60 days of submittal.

In addition, the new law stops local governments from creating additional restrictions for the ADU approval process. In particular, AB 68 restricts municipalities from imposing parking requirements and rules that restrict the floor plan and design of your ADU if it fits within the California standard.

If your ADU is less than 750 sq ft in size and 16 ft in height, and at least 4 ft away from your rear and side yard property lines, then local ordinances across the state cannot reject your ADU plans for outdated reasons. And even if your ADU is lot size larger than that, most zoning districts in the state are allowing for ADUs of up to 1200 square feet or more to be built in your backyard.

Because ADUs are built on properties with existing single-family dwelling or proposed housing, these ADU units are considerably more affordable than building a new home. They do not require additional space beyond existing property lines, dedicated off-street parking, or other expensive and oftentimes prohibitive requirements of trying to build an entirely new home. ADUs come with all the benefits of a completely functional and comfortable living space, as we'll cover in the next section below.

What is required in an ADU?

All accessory dwelling units must have complete independent living facilities. This means that the space must include some sort of studio or bedroom space, kitchen facilities, and bathroom at a minimum for development standards and safety code compliance.

This provides for a wide range of potential ADU floor plans, from small studios to spacious 1 bedroom ADUs to 2 or even 3 bedroom ADU units. Cottage has designed ADU units of all shapes and sizes for homeowners across the Bay Area, ranging from close to the minimum 150 square feet "tiny home" ADUs to as large as a 1200 square feet maximum floor area. Check out our post on how to choose the right ADU floor plan here.

Interested in learning more about ADUs and what kind might fit your needs? Check out our next article on the Different Types of ADUs here. Ready to talk more about how Cottage can help build the ADU of your dreams from start to finish? Contact us today using the link below for a Free, No-obligation Consultation & Estimate with one of our ADU experts!