Although the requirements for legal ADUs vary widely, some of the more common restructions include:

- The ADU must be smaller than the original housing unit

- The ADU must have designated parking (often relaxed in "walkable" neighborhoods)

- The ADU or the main house must be inhabited by the property owner or a blood/legal relative (also relaxed in some areas, or tightened to limit short-term rentals)

- The ADU must be compatible, in design, to the main house and the neighborhood

Some areas allow two ADUs on a single property., often with one being "attached" and another being freestanding.

(Excerpt from The SRES Professional)