The dado rail is one of those domestic features that people have very strong feelings about without necessarily knowing why. They either love it - it adds character, it divides the wall beautifully, it is period-appropriate - or they hate it - it is fussy, it is dated, it makes rooms feel smaller. Both of these positions are, in their way, correct. But neither of them is historical.
What it was actually for
The dado rail takes its name from the dado, the lower portion of a wall that runs from the skirting board to roughly chair height - typically somewhere between 70cm and 90cm from the floor. In classical architecture, the dado was the middle portion of a column's pedestal. When that terminology was applied to interior wall division, the rail became the horizontal moulding that marked the transition between the lower field and the upper field of the wall.
The original function was protective. In the Georgian period, when the dado rail began to appear consistently in domestic interiors, rooms were furnished with chairs that were placed against the wall when not in use. The rail protected the wall from the backs of the chairs - specifically from the chair rail catching the plaster and leaving marks. This is why dado rail is also known as chair rail in American architectural terminology, and why its height corresponds fairly precisely to where a chair back would make contact.
The Victorian expansion
By the Victorian period, the functional origin had not disappeared but it had been entirely subsumed by the decorative. Victorian interior design divided the wall into three distinct zones, each treated differently: the dado (below the rail), the field (between rail and picture rail), and the frieze (between picture rail and cornice). Each zone might have different wallpaper, different paint treatment, or different panelling. The complexity of this system was intentional - it signalled wealth, taste, and the kind of domestic ambition that characterised the Victorian middle class.
The wallpapers produced for dado-height application in this period are some of the most interesting objects in decorative arts history. Often heavily embossed and finished in relief, they were designed to withstand physical contact and still look considered. The Lincrusta panels popular from the 1870s onwards were essentially a form of continuous dado covering - robust, wipeable, and offering a texture that plain plaster could not achieve.
The twentieth-century rejection
The dado rail fell decisively out of fashion in the mid-twentieth century, and its fall was ideological as much as aesthetic. Modernism's rejection of ornament - Loos's famous assertion that ornament was crime - extended to every form of decorative elaboration, and the dado rail was an easy target. It was associated with Victorian stuffiness, with the pretension of the aspiring middle class, with an architecture of concealment and division rather than openness and honesty.
What replaced it was the smooth, undivided wall from skirting to cornice - or, in the most committed modernist interiors, no skirting and no cornice either. The wall became a plane, not a composition. This remained the dominant mode for about fifty years.
The return
The dado rail began to come back in the 1990s, went away again, and has now come back in a more sustained way. The current version is not the Victorian one - the three-zone wall with different wallpaper in each zone remains unusual outside of committed period-restoration projects. What most people are doing now is simpler: a rail at chair height, paint below, paint or paper above, often in colours that create deliberate contrast.
This version is decorative rather than functional, but that is fine. The history of domestic detail is full of elements that began as solutions to problems and persisted as expressions of preference long after the problems disappeared. The question worth asking is not whether your dado rail is original to the period of your house, but whether it is doing something useful for the room - dividing a wall that is too tall, grounding a scheme that floats, giving a room a sense of vertical structure. If it is, it belongs there.