An accessory dwelling unit is a second, smaller living space on a property that already has a house on it. It has its own kitchen, its own bathroom and its own entrance. Where it gets built is what the second acronym is about.
ADU: attached or within
An attached ADU shares structure with the main house. A converted basement with a separate entrance, a finished space above an attached garage, or a unit built off the side of the house all qualify. Because the structure, and often the utilities, already exist, an attached unit is usually the less expensive route.
DADU: detached
A detached accessory dwelling unit is a separate building in the yard. It is effectively a small house: its own foundation, framing, roof and utility runs. That costs more and takes longer, and in exchange it offers genuine separation, which is what most people actually want from the arrangement.
Why the distinction matters
Zoning treats the two differently. Setbacks, lot coverage, height limits and parking requirements can all apply differently to a detached unit, and Metro rules on this have changed more than once. Whether your lot supports a DADU at all is the first question to answer, well before anyone talks about layouts.
Which one is right
If you have usable yard and want real separation, detached is usually worth the difference. If you have an unused basement or garage and a tighter budget, attached can deliver most of the benefit for much less. The lot usually decides before you do.
