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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” might sound institutional, but it’s the most commonly-used term across the country to describe this type of housing. Because the full name is a mouthful, we use the shorthand “ADU” instead.

ADUs are defined by the fact that they’re a type of housing unit—NOT a standardized structural form. When learning about a new design concept like an ADU, it’s natural to want to know exactly what that concept looks like in the flesh.  However, ADUs vary in their physical form quite a bit. We want to embed the ADU design concept in or brains as a tangible object that we can mentally reference. Let’s broaden that mental model by exploring and understanding the range of common ADU types.