In Nouvelles Impressions d’Architecture, Libeskind (1998) writes "When architecture no longer deals with Space, all transactions, in which the container and the contained twisted together […] have come to an end". A systemic analysis can be performed morphologically, functionally or dynamically. The connection between the appearance and the generation of the form, human perception and experience, the processional nature of any system, is considered. The buildings of the Modern Avantgarde were raised during a very short time span of 20, sometimes just 10 years, in several different parallelly coexisting styles, coexisting also with newest developments in music, arts, physics, philosophy, economic and social theory and industrialisation. One of the nuclei of the movement was built by the housing programme, particularly suitable to foster innovation. While in more industrialised countries ways to solve social problems were seeked for, in the other European countries the new possibilities were seen as an opportunity to give a more prosperous image to cities, by raising density with blocks of flats for the middle class. The study will concentrate on European features of building stock which have not been covered by previous studies, namely the spatio-functional research of the interior organisation of the dwelling in the blocks of flats for the middle class. The study proposes a heterogeneous model in which a zone has instead of a unique function a unique vocation. Zoning results as a structural product in the superposition and interpenetration of textures (sub-systems of the life-frame elements able to respond to the functionally requested situation) of morphologic elements, thanks to the co-operation process of human activities. There is a complex zoning with operational and organisational value. As case studies will be considered: - Milan 1920-1940; - Bucharest 1920-1940; - Athens 1919-1939; - forerunners of and Avant-Garde in Budapest 1896-1939.