What’s an ADU: Accessory Dwelling Units

An accessory dwelling unit, usually called an ADU, is an additional housing unit on a single-family residential lot. The term accessory dwelling unit is an industrial-sounding name, but it’s the most commonly used in residential housing.

The fact that the structure is a secondary housing unit is what defines an ADU. When learning about concepts, it’s natural to want to know what that concept looks like in the flesh. We want to visually embed the design concept in our brains as a tangible object that we can mentally reference.

However, ADUs vary in their physical form quite a bit, so allow me to broaden that mental model by exposing you to the range of common ADU types, in order to better understand what they are. Call our office today for more information. Five Star Roofing can price-match competing offers. Our state-licensed team also keeps warranties for any occasion.

What ADUs Have in Common

While their structural forms vary, ADUs share some common traits and face common design and development challenges. These similarities include:

• The fact that they’re secondary housing units on single-family residentially zoned lots places ADUs into a unique category of housing. And ADUs also have some other distinguishing characteristics that help further define, differentiate, and distinguish them from other housing types.
• ADUs are accessories and adjacent to a primary housing unit.
• ADUs are significantly smaller than the average US house.
• ADUs tend to be one of two units owned by one owner on a single-family residential lot.
• ADUs tend to be primarily developed asynchronously from the primary house by homeowner developers.
• A large range of municipal land use and zoning regulations differentiate ADU types and styles and dramatically affect their allowed uses
• Vast numbers of informal ADUs exist compared to permitted ADUs.

Types of ADUs

• Detached ADU New Construction
• Detached new construction ADUs, also sometimes called backyard cottages, granny flats, laneway houses, or DADUs, depending on the jurisdiction.
• Detached ADU
• Garage conversion ADUs.
• Above Garage ADU
• ADUs above a garage or workshop, or attached to it. In some areas, these may be called garage apartments or carriage houses.
• Bump Out ADU
• Basement conversion ADUs, also commonly called basement apartments, mother-in-law units, in-law units, secondary suites, English basements, accessory apartments, and a host of other names.
• Basement ADU Interior
• Internal ADUs, where part of the primary house beside the basement is converted to an ADU.

Why Do Cities Want to Improve Their ADU Codes?

Well, for starters, most households in the United States are now 1-2 person households. Yet, most of our legacy housing stock, and even our new residential housing stock, is designed for families of 4 or 5 people. That may have made sense 70 years ago. But things have changed. The average household size dropped from 3.67 in 1940 to 2.53 in 2016 (US Census data).

Homes with 3-4 bedrooms no longer match the demographic realities of the United States:

• Percentage of households for 1-2 people has increased
• 1-2 person households now represent 62% of the country’s households. Only 38% of the nation’s households have more than 3 or more people in them.
• Close to 2/3rds of the population in the US are living in 1-2 person households!
• Year by year, 1-2 person households are forced into eating up the single-family housing stock (housing pellets, if you will) that was designed for nuclear families, not because they want or need to live in big homes, but because there simply aren’t enough houses built in residential areas that were actually designed for 1-2 person households.
• Among other demographic factors at play, single-person households have become extremely common in major cities, representing more than the households of many cities.

Why Cities Care About ADU Development

There are a lot of reasons that municipalities may want to spur ADU development. Here are a few:

Economic

ADUs provide flexible dwelling options in central city neighborhoods, utilize existing governmental infrastructure (e.g. roads, sewers, schools), and reduce the demand for expanding infrastructure in far-lying reaches of a developed metropolitan area.

Environmental

ADUs provide housing with a relatively small environmental footprint. New, detached ADUs provide rental housing that is 44% smaller per capita than standard, new single-family rental units. And new ADUs overall provide housing that is 33% smaller per capita than standard, new single-family units.

Social

ADUs provide more affordable housing options in residential neighborhoods without dramatically changing the character of a neighborhood as much as other new housing forms may.