In Portugal, the introduction of social housing policy came in 1918 and began to manifest in many projects in Lisbon during the inter-war period.  This change was imposed due to a housing shortage, causing design to deviate from the traditional low-rise garden city architecture and rather towards high-rise apartment buildings.  This shift was especially aided by the use of reinforced concrete as a construction system.  In 1935, Étienne de Gröer was in charge of planning the extension of Lisbon in which he employed the parcellation of the area into geometric blocks.  Many of these blocks became the sites of public housing projects, which developed into two distinct typologies.  One type consisted of 3 upper floors with up to 8 residential units.  Reinforced concrete construction allowed the use less interior load-bearing walls, thus providing more freedom in creating a functional floor plan.  The second building type housed units that were designed in a similar way.  The distinction between the two types is that the second consists of 5 or more upper floors, with often more units per floor.