Situated within the boundaries of the former headquarters of the Royale Belge insurance company, the project plans to keep the existing buildings in order to conserve the environmental and architectural quality. This exceptional site has one of the finest examples of 1970s office architecture, designed by architects Pierre Dufau and René Stapels. The historic building, a cross of steel, concrete and glass, is located at number 25 boulevard du Souverain, alongside the Ten Reuken ponds and on the fringes of Soignes Forest. The location of the future Souverain 23 project is inspired by the existing building at Souverain 25. The idea is simple, consisting of duplicating the building and then adapting it to a housing type development and the layout of the site. The volumetry is also inspired by the Souverain 25 building, in that it consists of a group of 4 buildings in the form of an open book. The starting point of the open book shape is the cruciform shape of the existing Souverain 25 building. The materials have also been chosen to ensure continuity with the existing building. The living room and terrace (open book) will be built of bronze anodised aluminium materials, vertical bronze-coloured railings and a screen of bronze-coloured smoked glass. The window frames will be made of anodised aluminium, also coloured bronze. The other façades will be made of a rougher, opaque material, such as polished prefabricated concrete, or a layer of bluestone or dark brick. The idea is to create a very pronounced contrast between the two types of façade, to echo the contrast between the surrounding nature and the rigorous geometry of the existing and planned buildings. The composition of the façades is simple. Very open to the south and to the west, emphasising the views and orientations. All the apertures are of the same dimensions, and reflect a rigour which also provides continuity with the Souverain 25 building. This rigorous architecture is sober, basic and elegant. The roofs will be green roofs, and useable by the occupants of the buildings; this will enable recreational activities while enjoying exceptional views and enhanced privacy. The car parks will be accessible via a ramp located at the site entrance. The parking spaces will occupy the first two basement levels. The existing levels -3 and -4 could be allocated to a large storm basin and rainwater storage tanks.