This paper gives a general overview about the needs for improvement of urban building envelops of post-war large scale ‘low cost’ housing projects in Belgium. Although the situation is comparable for all greater cities of the country, the description is mainly referring to the characteristics in the northern part (Flanders) and the region of Brussels. It explains the needs, as they appear in different types of housing projects realised after 1945 and the way they are experienced to-day, based on modern standards of safety and comfort. Different aspects of needs are summarised i.e. the planning, the architectural, the technical and the social and economic aspects. The paper gives some ideas about possible solutions and priorities which can be applied in Belgium. Some experiences from concrete cases are illustrating the text.