Bruxelles Environnement building: sustainable, transparent, & flexible with slim floor beams

Detailed information

The new building of the governmental organisation, Bruxelles Environnement, was designed to stand out in many ways. Its compact shape is the result of the strict ecological design concept and the stringent standards of liability, while its interior organisation reflects openness and transparency towards the citizens.

The author of its design and ecological quality concept is the Dutch architectural office cepezed who were asked to create a building worthy of housing the city's environmental agency to set an example in the field of energy-efficient and sustainable construction. Bruxelles Environnement is now the largest passive construction in Belgium and was certified with BREEAM Excellence.

Intelligent air conditioning, accessibility, compactness and functionality, and iconic value are just some of the many features in this transparent building where all components are in visual contact with each other and filled with natural light. This is made possible thanks to a mixed steel and concrete structure that translates the concept of openness into spatial design.

Transparent, open, & lightweight structure with ArcelorMittal SFB beams

The building's structure combines steel and concrete: a metal frame (steel columns and beams), prefabricated concrete floor slabs, and on-site poured concrete walls. Whereas the steel provides the load bearing capacity, the concrete stabilises the structure. The steel skeleton is mainly left visible and with its white colour it contributes to the transparent and lightweight structure.

The choice of steel for the main structural elements was a logical result of the sustainability requirements. Steel lends itself to prefabricated construction which offers a number of advantages: numerous components were manufactured in the workshop and could then be assembled quickly and accurately on site. In case of the dismantling of the building, the steel can be reused completely.

In total, around 900 tons of S355 grade steel were used for the building's structure in the form of structural tubes as columns and rolled sections as floor beams - both in various types, lengths, and thicknesses.

ArcelorMittal supplied their innovative SFB beams (slim floor beams) - an HE section with a plate welded to its bottom flange to support the floor slab. This way, the slab thickness can be reduced and floor height can be gained.

For the Bruxelles Environnement building, the SFB beams are made of HEB 260, 240, and HEM 280 sections with a 15 or 25 mm plate welded to their bottom flanges. The tubular columns were equipped with a welded plate to extend its round shape and ensure perfect support for the floor beams for correct transmission of the loads. After fabrication, the plate and the column were milled to ensure they are perfectly parallel and in direct contact with the beams.

The steel structure is protected with intumescent paint free of volatile organic compounds to meet the BREEAM requirements.

Out of the ordinary: roof & facades

The integration of the roof with the facades provides the Bruxelles Environnement building its unique appearance. The relatively small front facade prevents heat loss, and the domed roof merges practically invisibly with the facades. Although they contain a lot of glass, the facades contribute significantly to the insulation and airtightness of the whole building, and alternate strips of triple glazing with strips of black highly insulating mineral wool sandwich panels are mounted on extruded aluminium profiles. On the front and rear facades, steel sheets alternate with photovoltaic panels and a large glazed strip above the atrium.

The roof is made of a standing seam system of black, galvanised, and enamelled steel sheets with photovoltaic panels on top. The ventilated space between them protects the building and the photovoltaic panels against summer overheating. On the edges of the standing seam roof, a support structure was placed that acts as load bearing structure for the upper roof construction. From an aesthetic point of view, this fits very well as the black steel sheets are in the same line as the curtain walls. In addition, several hidden gutters were incorporated into standing seam roof.