Under the title of 'Living as an Urban Roof', Piet Blom designed a city composed primarily of two levels: a public space on the ground floor and habitats above, forming 'the roof of the city'. Blom did not elaborate the ground floor but he sketched public life with head words and free associations. With this exceptional design Blom attained a living density of 100 houses per ha. In 1965 the 'Living as a common urban roof' study was compiled in book form and edited by the Roof Tile Manufacturers' Association, Nedaco.
Blom's ideas did not stay captured in a folder. A subsidy for experimental house construction, attributed to the district council of Hengelo provided Blom with an opportunity to truly realize his concept of an urban roof. In 1973 the completion of the 'Kasbah', an urban roof of 184 houses took place in Hengelo. Blom designed three different basic types, combined into five different types of housing. This project reached a housing density from 100 dwellings per hectare