Loos believed in designing space in a new and radical way, where there are no ground floor or first floor, but rather adjoining continual spaces. ‘Loos House’ on Michaelerplatz, completed in the centre of Vienna, 1912, is arguably the first demonstrable example of Loos’ belief that interior spaces were more important than the exterior façade, in contrast to the highly ornate Hofburg Palaces St Michael’s wing situated within the same square. Thus, Loos pioneered the concept of ‘Raumplan’ (spatial plan) in Architecture. Raumplan employs varying room heights depending on their functions and importance for efficient use of interior space through visual connections and spatial illusions that impact the flow of a building through carefully considered composition of adjoining spaces. 

This means that more private areas with lower ceilings are connected through stairs, and visually connected using view-throughs with higher open rooms. The different ceiling heights cause a break in the horizontal layering of the house. This leads to complex space structures which are made accessible by an intricate vertical use of circulation. Through this innovative type of free thinking, Loos was able to create more living space within the same footprint of foundations. Loos would go on to use this method in residential projects: Tzara House (1926), Moller House (1928) and Villa Muller (1930) are outstanding examples, howev er even in the small footprint of the Model Houses (1931), Loos was still able to create the concept of space and movement using Raumplan.

Arguably the best example of the use of Raumplan is in the Villa Muller (1930) in Prague, Czechoslovakia. The Villa Muller design consisted of the use of rectangular containers that interconnect to create the interior spaces. These forms also connected the building exterior and the pleasing 3:2 aspect ratio, but did not reveal the spatial genius of the interior. In fact, while the Raumplan concept is considered today as revolutionary, the Villa Mu ller was until recently only praised for its cubed like façade, as the layout of the interior was wildly misunderstood and regarded as old fashioned. 

To guarantee the function of Raumplan there are complex vertical connections. through the spaces: the continuous height staircase connects the basement to the roof, whereas the non-continuous staircase provides access to the spaces that vary in height. Loos realised this connection in the Villa Muller with a small staircase and penetrated walls, and created a spatial sequence as you arrived in the entrance hall, which raises in height to 4.5 meters, whereas adjoining spaces, the boudoir and dining room reach just 2.1 meters in height. This in effect created three smaller spaces, but connected to one large space