An atrium is a continuous indoor open space of substantial width and at least 5 floor levels high. Only spaces inside regular multi-story buildings qualify as atriums; large indoor spaces in halls, religious structures, monuments, and other special construction types are not considered atriums.

When multiple buildings open onto the same atrium in a shared podium, the atrium may be assigned to each building. A light court or any courtyard which is open to the sky, or which is not fully enclosed, does not count as an atrium.

The five-floor minimum and enclosure apply to a broad, continuous space within a regular multi-story building. A planted rest area below that height can be a wintergarden; a large volume in a hall or religious structure remains outside this particular atrium definition.