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Accessory Dwelling Units – ADUs    Dwelling unit    

What is an ADU: Accessory Dwelling Units explained

An accessory dwelling unit, usually just called an ADU, is a secondary housing unit on a single-family residential lot. The term “accessory dwelling unit” is a institutional-sounding name, but it’s the most commonly-used term across the country to describe this type of housing. While the full name is a mouthful, the shorthand “ADU” is better.

The fact that it’s a secondary housing unit—rather than a given structural form—is what defines an ADU.. But, when we’re 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.

Types of ADUs

Here are images of some of the common structural forms of ADUs (as well as some of the other terms you might hear to describe them).

1)  Detached new construction ADUs, also sometimes called backyard cottages, granny flats, laneway houses, inlaw unit or DADUs, depending on the jurisdiction:

2) Garage conversion ADUs

3) ADUs above a garage or workshop, or attached to it. In some areas, these may be called garage apartments or carriage houses:

4) Addition ADUs or “bump-out ADUs”:

5) 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.  Not Common at all in California

6) Internal ADUs, where part of the primary house besides the basement is converted to an ADU.

Garage conversion ADU.jpg


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