The Smart Home Addition: Why ADUs Are Here to Stay

The name lacks charm to say the least. “Accessory dwelling unit,” or “ADU,” though perfectly descriptive in a drab sort of way, doesn’t exactly evoke an appealing living space. At Dwell, we prefer the term “backyard house,” which is at least less clinical. No matter what you call them, ADUs are popping up behind more and more homes all over the United States.

We define them roughly as secondary, self-contained habitations on the same lot as a larger house. Picture a smaller building in someone’s backyard or an attached but autonomous apartment, though we’ve seen them in all kinds of shapes and sizes. In many municipalities, they have to have a bathroom or other features to qualify as an ADU, but no matter what they look like, more and more cities and states are allowing them on once single-family zoned properties, which makes sense. The single-family home on a single-family lot that dominated the postwar suburbanization of America no longer works for many people.

Different ways of using our homes that were emerging before the pandemic have become the norm, with houses frequently doing double or triple duty as workplaces, schools, gyms, theaters, and any number of other uses—basically small cities. Whether or not you commute to an office, if you have a laptop, you’re probably doing some amount of work from home. No matter how versatile a kitchen table you have, a separate building for one or many of those activities seems appealing.

At the same time, households are changing. We often see homes where families have chosen to have parents move in as they get older and need more care—or they want grandparents on hand to help with childcare. We also see adult children living at home longer as housing costs exacerbated by interest rates prevent them from buying a home or even renting at a rate compatible with typical incomes in some places. America is now joining other parts of the world where living at home into adulthood is the norm. We’ve also seen people priced out of the conventional housing market join forces and pool resources to create their own live/work compounds. With those shifts, an ADU in the backyard can be a great way to keep friends and family close—but not too close.

Many places where housing costs have skyrocketed have adjusted restrictive zoning laws to allow accessory units in an effort to create desperately needed inventory. Minneapolis and Saint Paul were early adopters—as was the entire state of California as far back as 2017. You can even count potential rental income from an ADU when applying for a mortgage, and, in California, you can sell one you’ve added to your property, like a condo.

But ADUs are not always the housing cure many people hype them to be. For example, the same laws aimed at building affordable rentals have also permitted luxe pool houses and all kinds of vanity square footage, which is hardly going to solve the housing crisis. Opponents of zoning changes have a point where loosely written regulations have allowed short-term rentals to turn historic neighborhoods into hotels. Also, I’m always saddened by the idea that you should feel compelled to monetize and maximize gains on every square inch of your property. Treating your home as merely an asset rather than, well, your home is heartbreaking. That said, anything that presents a pressure valve for a bottled-up housing supply can certainly help.

Like any kind of construction, the process and cost of building an ADU varies as widely as the designs we see people come up with and the regions where they live. We’ve featured ADUs that cost from pennies up to thousands per square foot in our weekly Budget Breakdown column and in our annual Money Issue, where we ask designers and homeowners to walk us through the real numbers behind a project—a level of transparency that’s unfortunately rare in architecture magazines. We’ve also seen that the potential speed and simplicity of prefab construction make it an attractive way to add an ADU to a property, so much so that our newsletter dedicated to prefab homes and the companies that build them almost always includes an ADU or two. (They also crop up frequently in our tiny homes newsletter if you want to see particularly small footprints.) As the ADU market has expanded, we’ve seen prefab companies step in to serve it, and prefab promises faster timelines and a better up-front understanding of costs. But the price points they often tout can be deceiving. We’ve seen permitting, site work, electrical and septic upgrades, delivery, and other factors make unbelievably affordable-sounding prefab structures cost much more than conventional construction. We love prefab design, but it’s not one-size-fits-all.

Dwell was an early champion of ADUs, and I support allowing them in most contexts. We’ve covered hundreds (and even designed our own Dwell House with Norm Architects and the California company Abodu). They’re interesting because how often does a new type of house emerge? ADUs respond to the challenges and aspirations of contemporary life. They have the potential to transform neighborhoods, and they have given architects and builders a new creative territory to explore, which in turn gives us new stories to tell—and if you think of a more exciting name than “accessory dwelling unit,” you’re hired.