Understanding ADUs: What They Are & What They’re Not

As housing demands evolve and homeowners seek smarter, more flexible ways to use their property, Accessory Dwelling Units—commonly known as ADUs—are gaining serious traction. The many options available for ADUs offer a creative solution to housing challenges while maximizing space and value. But what exactly is an ADU—and just as importantly, what isn’t one?

What Is an ADU?

An Accessory Dwelling Unit, also known as an ADU, is a secondary, self-contained residential living space located on the same lot as a primary home. Sometimes called a granny flat, in-law suite, backyard cottage, or secondary suite, an ADU can take many forms such as:

• Detached units like a small cottage or guest house in the backyard.
• Attached units which are physically connected to the primary residence, often through shared walls.
• Interior conversions, for example, transforming a basement or attic into a livable space.
• Garage conversions – reimagining an existing garage as a livable dwelling.

A few key features to keep in mind that define an ADU include:

• It is a permanent residential unit, not a temporary structure.
• It is legally part of the same property as the main house and cannot be sold separately.
• It provides independent living facilities, which means it must have its own kitchen, bathroom, sleeping area, and typically a separate entrance.
• They can be attached to the main house, within it (such as a basement apartment), or completely detached (such as a backyard cottage).
• They often share utility connections with the main residence.

What an ADU Is Not

While ADUs are incredibly versatile, they’re often misunderstood. Understanding what does not qualify as an ADU is just as important as what does. These are NOT an ADU:

• A bedroom, bonus room, or finished basement without a dedicated kitchen and bathroom
• A second kitchen in the main house that does not have its own living space and full bathroom
• A space that does not have a lockable, private entrance
• Temporary structures (like RVs, trailers, or tiny homes on wheels). ADUs must be permanent and built on a foundation.

Common Misconceptions

• ADUs are not just for rental income, they can serve as flexible living spaces for family, guests, or work.
• Building an ADU is not always prohibitively expensive or time-consuming; costs and timelines vary by design, location, and contractor.
• ADUs do not necessarily decrease property value; in many markets, they can increase it by adding functional living space.
• They’re not always suitable for short-term rentals (for example listing on Airbnb) because many municipalities prohibit short-term rentals of ADUs to encourage long-term housing stability.

Why ADUs Matter

ADUs serve a range of purposes: they can house aging parents, provide income as rental properties, or offer space for young adults or guests. They’re recognized for their flexibility, smaller environmental footprint, and ability to gently increase housing density without changing neighborhood character.

At ArchitectureEL, Inc., we view ADUs not just as an architectural trend but as a meaningful response to the housing crisis, and its shifting demographics, affordability challenges, and lifestyle needs. Whether you’re exploring an ADU to support multigenerational living, generate rental income, or simply make better use of your property, understanding what they are—and what they aren’t—is a critical first step.

Ready to Explore an ADU?

If you are, it is important to remember that even though they’re compact, ADUs require thoughtful design, permitting, and construction—ideally with an architect who understands zoning and local building codes. We’d love to help you on this journey and are here to help you navigate the process from concept to completion. Contact us to schedule a consultation and learn how we can help bring your ADU vision to life.