A one-stop source about accessory dwelling units, multigenerational homes, laneway houses, ADUs, granny flats, in-law units…
As noted elsewhere on this site, one of the defining characteristics of accessory dwelling units (ADUs) within the real estate, lending, and planning fields is that they are second units on otherwise standard single family properties. No matter what their physical form (backyard cottage, basement apartment, etc) they are part of the property with the main house; they have the same owner as the main home, and cannot be bought and sold separately.
To the extent that people in the real estate, lending, and planning fields are aware of ADUs at all, they will assume that ADUs follow this convention of having the same owner as the main house.
However, it is conceivable that an ambitious and creative developer could split the main home and ADU into condos — after which the ADU would only be an ADU in an architectural sense — i.e. it would be a basement apartment, a backyard cottage, or whatever. But in a legal sense, the property would be a condominium development with exactly two units, each of which could be bought or sold on its own.
Currently, the “condominium” model of ADU development and ownership is incredibly rare. Unless otherwise noted, all posts on this site assume the standard model, where there is a single owner for both the main home and the ADU.
— Martin (one of editors)