The dado rail is traditionally part of the dado and, although the purpose of the dado is mainly aesthetic in modern homes, the dado rail still provides the wall with protection from furniture and other contact. Traditionally, the height of the dado rail is around 36" or 900 mm, which was a suitable height to protect the wall from the backs of chairs. Since the original purpose of the dado treatment is not applicable in modern homes, it is common to see dado rails at 1200 mm or even 1500 mm from the floor.
Dado rails are also sometimes applied to a wall without the full dado treatment. The purpose of the rail in these cases may still be protective, and it is common in environments where walls are subject to a lot of wear and tear, such as shopping centres and hospitals.