A rooftop for a 290 m² parliamentary hall in the Vaud cantonal parliament, built atop 13th Century ruins, nested snuggly into the picturesque skyline of the old city of Lausanne. Located between the Château Sainte-Maire and the Lausanne Cathedral, the parliament hall, once inaugurated in 2017, will be endowed with a roof supported only by its base, a glazed atrium letting in natural light, and a gallery overlooking the conference arena for citizens and journalists. The novelty of the almost 15-meter tall roof lies in its beam-free design.
The roof’s innovative design makes the structure remarkably robust, with little wasted space. Normally, wooden roofs are carried by a framework of beams. The most fragile points of these structures are located where the beams are connected. If one beam fails, the stability of the entire roof can be compromised. By working with large, preassembled wooden panels that make up both the structure’s surface and its load bearing elements, the proposal made by Weinand and his team distributes all forces along the entire surface of the roof, rather than concentrating it in specific locations.
The roof’s beamless design was made possible thanks to the development of cross-laminated timber panels, a major innovation in wood technology. By gluing wooden boards so that the directions of their fibers alternate from layer each layer, these panels provide high strength, even for very thin panels. “Proposals based on technological innovations rarely receive public mandates, because of the risks associated with them. The fact that we had extensive research to back our claims definitely played in our favor,” Yves Weinand says, director of EPFL’s Timber Construction Laboratory.
Description of project by Bonell i Gil Arquitectes
The new building, which opens its door on 14 April, was constructed with a budget of 25.410.000 million euros. In its role as representative of this democratic institution and for its strategic location between the cathedral (built in the 12th century and reconstructed in the 19th by Viollet-Le-Duc) and a 14th-century castle, it now stands as the last piece in the puzzle, visually balancing the symbolism of the religious and military institutions.
Three aspects of the intervention are particularly worthy of note: the plenary hall and its roof, the entrance and the salle des pas-perdus.
To address one of the architectural challenge of increasing the volume of the plenary hall of the Grand Conseil to adapt it to new parliamentary requirements, innovative concepts of construction and technology were used. Specifically, the floor plan of the hall gains surface area by means of a projection over the historic foundation walls, and two of its façades open up to offer views of the city, Lake Geneva, and the Alps. The project also set out to give the roof, in addition to its functional role, a sufficiently representative presence to insert the building into the urban space of the old town, between the castle and the cathedral. To this end, it is designed with an pyramidal form that ensures environmental comfort through its skylight, and its air-conditioning system is based on the principle of ventilation of termite mounds.
Meanwhile, the discovery of historic ruins in one of the walls of the entrance foyer prompted the relocation and redesign of the stairway communicating the various floors. Created in steel and wood, it rises through the triple-height space and folds to form a vantage point. Its visual impact is offset by suspending its structure using a single tight.
And, finally, the salle des pas-perdus, the name given to large spaces in public buildings for walking around and meeting, has had its old stone floor recreated and its roof reinterpreted with concrete moulding.
