Accessory Dwelling Units: What Exactly Are They?

The demand for ADUs is steadily increasing and many are wanting to understand these units and their benefits further. In this article, we explain what ADUs are, provide some examples of different accessory dwelling units, and discuss the public and city interest in more ADUs.

Also known as mother-in-law cabins, secondary suites, cottages, and self-contained apartments, accessory dwelling units refer to small, second homes attached to or on the same property as your primary residence. These include a small house on a foundation in the back or side yard, an apartment over or attached to the garage, a basement apartment, and more.

All ADUs share a handful of traits, design aspects, and development obstacles.

• They're in a unique housing category.

• They are considerably smaller than the average home or unit.

• They are an accessory to or adjacent to the central household unit.

• They are usually developed and built at a different time than the primary home.

• ADUs are one out of two units that are owned by the same owner on a single-family lot (residential).

• ADUs are differentiated from other types of properties because of zoning regulation and the range of municipal land use.

• More informal ADUs exist than permitted and documented ADUs.

All of these distinctive characteristics make ADUs a unique type of housing. With a more cohesive language and understanding of accessory dwelling units, there's now a deeper understanding of the best practices in ADU development than ever before.

There are various structural forms of accessory dwelling units. These include:

• An ADU above a workshop, above a garage, or attached to a garage—known as carriage houses and garage apartments.

• A detached ADU new construction—known as granny flats, mother-in-law cabins, backyard cottages, or laneway houses. It depends on the jurisdiction.

• Garage conversation ADUs

• Bump-out ADUs also known as Addition ADUs

• Basement conversion ADUs

• Internal ADUs - a part of the home besides the basement is converted.

The average size of a household in America used to be four or five people. These days, the average is two to three. Despite this considerable difference, most of our past and present housing is designed for families of four to five. That may have made sense 80 years ago, but not today because households with three to four bedrooms are a poor match for the American demographic because our average household size is no longer that large and the average household income is nowhere near enough to support such a large home, as it's not just houses that are more expensive but also the upkeep for it.

Those who live in smaller households have had trouble securing housing that's an appropriate size. Often these folks have to rent or buy a larger home than they need because it's simply all that's available on the housing market. For these reasons, the demand for accessory dwelling units is only expected to rise.

The environmental footprint of ADUs is barely noticeable compared to larger family homes. A new ADU that's detached is about 44% smaller than a standard home. Overall, new ADUs are about 33% lower than the standard. Smaller homes, apartments, and living spaces use far less energy regarding habitation, construction, and deconstruction through the building lifecycle.

Accessory dwelling units can offer more affordable and flexible real estate options in metropolitan cities. Usually, the dwelling units utilize governmental infrastructure that already exists like schools, sewers, and roads. For this reason, accessory dwelling units reduce the need for expansion in already overcrowded central cities.

ADUs benefit the neighborhoods they're in because they can offer growth without much physical expansion or change in the neighborhood character.

By offering smaller, more affordable housing options, ADUs can help alleviate the mismatch between available housing and the needs of smaller households.

ADUs can be great fun to aesthetically design and decorate—and, it's much more economical. Because a renter or an owner has less to buy, they can usually spend nicely on what they do choose to have in the home. This extra bit of economic and decorative flexibility leaves some ADUs looking far nicer than regular homes!

Here are a few tricks to make the most out of your accessory dwelling unit:

• Coordinate the outside of the ADU with the main home's exterior.

• Place your windows as high as possible to let the max amount of light enter.

• Contemplate vaulted ceilings. They create more room.

• Cultivate open spaces--don't waste any square feet!

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This post was originally published on 08-28-2020. It was updated on 07-26-2024 to reflect the latest information.