applications in Brussels
The most popular heavy prefab system in Brussels was the Barets system. Thanks to the flexibility of the system, it was used not only in high-rise buildings but also in the more common low-rise housing projects. The National Institute for Housing (NIH) used it to construct a social housing project of 140 low-rise houses in Woluwe-Saint-Lambert. These houses were part of the district Les Pléiades (begun ca. 1961), designed by the architects of Groupe Alpha. The loadbearing façade panels, constructed on site, consisted of layers of plaster, insulation (reed panels), and reinforced concrete, with a washed finish and a plinth in black gravel. The Pleiades district also included high-rise buildings and traditional houses. Comparing the construction systems showed some of the benefits of the Barets prefabrication system, such as thinner walls, a lower material usage, no cracks due to the shrinkage of concrete, rapid construction, no external skeleton frame, and reduced heat loss.
La Magnanerie and La Cité Modèle are probably the most famous examples of the Barets system in high-rise apartment buildings. Shaped like a boomerang and 16 storeys high, La Magnanerie in Forest (1955-1958) was designed by architect Claude Laurens, who was succeeded by architect Jacques Cuisinier. The technique used to construct the building changed halfway through the project: above the portal frames at ground level, half of the block was constructed with cross-walls (not of a particular system), while the other half was constructed with the Barets system. No details about this change in the construction are known.
The Cité Modèle is the most extensive example of the Barets system in Brussels, although only the high-rise buildings of the first phase were built this way, while the others built with the Cauvet system. In its entirety, the Cité Modèle is a very extensive social housing complex, combining several housing typologies, from terraced single-family housing to high-rise towers. It was designed by an ad hoc collective of architects: Renaat Braem, Victor Coolens, Groupe l’Equerre, René Panis, Groupe Structures, and Jean Van Doosselaere. The architects did not contemplate using the Barets system. Rather, in the first tender round, some bidders proposed heavy prefabrication, as it had a (minor) positive impact on the budget; the architects accepted the idea and adjusted their drawings. Originally planned to be part of the 1958 World’s Fair in Brussels, the project was only finished in 1972.
The first five high-rise blocks (I, II, III, V and VIII) were constructed by the construction company Entreprises Générales des Travaux d’Anderlecht (EGTA) using the Barets system. The floor and wall panels were all cast horizontally in concrete moulds. For the floors, which spanned approximately 5.60 m and were 15 cm thick, retractable metal tubes were inserted to create hollow floor slabs (seven cavities of 8 cm in diameter per meter). The wall panels were 14, 17, or 20 cm thick, depending on their location in the building, and one story high. All the pipes, fixtures, and door and window frames were put in the moulds before the concrete was poured. The stairs, too, were prefabricated: the flights of stairs were made as single elements, perfectly smooth and completely finished. Three days after the elements were cast, they were de-moulded and lifted into position by a crane. Once put in place and connected with in situ concrete, the panels formed a stable, reinforced concrete structure that supported both vertical loads and wind loads.
Halfway through the project, a second round of tenders was organized and a new contractor (Strabed) was chosen, who used the Cauvet system to construct the apartment buildings IV, VI, and VII. In these buildings, the floor slabs spanned 5.50 m. They consisted of 5 cm of reinforced concrete at the bottom, an 11 cm layer with the rectangular cavities, and a 3 cm top layer of reinforced concrete. The wall panels had five layers: 4 to 6 cm of reinforced concrete (whether or not with a façade finish), 3 cm of glass wool insulation (compressed to 2 cm due to the weight of the concrete), an intermediate layer of reinforced concrete of 3 to 4 cm, a cavity layer, and a final layer of 3 to 4 cm of reinforced concrete, forming the inside surface. Except for the layer of insulation and details of the cavities, the Cauvet and Barets systems worked on the same principles.