Piano nobile

The German term is Beletage (meaning "beautiful storey", from the French bel étage).

The reasons were so that the rooms above the ground floor would have finer views and to avoid the dampness and odours of the street level.

That is especially true in Venice, where the piano nobile of the many palazzi is especially obvious from the exterior by virtue of its larger windows and balconies and open loggias.

Kedleston Hall is an example of this in England, as is Villa Capra "La Rotonda" in Italy.

In Italy, especially in Venetian palazzi, the floor above the piano nobile is sometimes referred to as the "secondo piano nobile" (second principal floor), especially if the loggias and balconies reflect those below on a slightly smaller scale.

An early-15th-century piano nobile at the Palazzo dei Diamanti , Ferrara. Its larger windows indicate its superior status compared with the rooms on the floor below.
The Beletage of Dresden 's Villa Martha , built in the 1870s
At the 18th-century Kedleston Hall in Derbyshire , the piano nobile is placed above a rusticated ground floor , and reached by an external staircase. The uppermost windows indicate that the upper floor is of far lower status.
The Beletage of the Palais Gise in Munich is on the second floor (third floor in American terms).
At the Palazzo Barbarigo in Venice, the floor above the piano nobile is of almost equal status, so it is referred to as the secondo piano nobile .