In a country where concrete is king, construction of wood buildings is reaching new heights by hedging on verticality. There are currently around thirty high-rise wood building projects underway in France and hence the country has moved into position as a world leader in this field.
By 2020, France’s two tallest residential and office towers with engineered timber frames will rise above the Belcier district in Bordeaux, close to the city’s Saint-Jean station. At 57 and 50 metres in height respectively, the Hyperion tower (see focus), designed by architect Jean-Paul Viguier and to be built by Eiffage and Woodeum, and the Silva tower, designed by Art&Build and Studio Bellecour, with Kaufman & Broad as promoter and developer, will compete to snatch existing world records for engineered timber-framed high-rise buildings from Norway’s Treet Building in Bergen (51 metres) and Canada’s Brock Commons in Vancouver (53 metres), although the latter will soon be deposed by the HoHo Tower in Vienna, Austria, at 84 metres.
The two designs for Belcier were selected following a call for projects held in 2015 by Bordeaux Euratlantique, the public body charged with urban development in the Bordeaux area. In March 2016, it pledged to build 25,000 m² of wooden spaces every year for 15 years as part of this regeneration scheme with Operation of National Interest (OIN) status, which constitutes one of the largest urban planning developments in France (over 738 hectares). Beyond the momentum at local level, Hyperion and Silva are proponents of a wider movement that embodies a strengthening trend: currently, there are medium and tall height wood building projects flourishing right across France (including Ecopolis in Dijon, Etang d’art in Angers, Opalia and Wood Up in Paris, SequoiaH in Nancy, and Palazzo Meridia in Nice).
Several factors are driving this trend: in the context of urban densification where improved energy efficiency and reduced greenhouse gas emissions are ever more important, wood offers a solution to one of the major conundrums in sustainable city development. On top of being a natural raw material with properties of insulation and durability, wood is also an efficient, natural carbon trap. According to Philippe Zivkovic, co-president of Woodeum: “wood can store 460 kg of CO2 per m³ whereas concrete emits 471. By way of example, construction of a new gas-heated 60 m² wood apartment generates such a highly positive ‘carbon count’ that it would take forty years’ worth of heating before it returned to zero”.
Thirty high-rise wood buildings currently planned in France
“The drive to reduce the carbon footprint has been gathering strength since the ‘Grenelle de l’environnement’ law in 2009, which saw terms such as ‘energy efficiency’ and ‘environmental performance’ become part of the conversation. The pace quickened following the Paris Climate Agreement (COP 21) in December 2015,” explains Patrick Molinié, construction development lead at the French Institute of Technology for Forest-based and Furniture Sectors (FCBA), the research and innovation centre for the timber industry in France, and gained additional impetus with the first international Woodrise Congress on Hi-Rise Wood Buildings” (see separate article, page ??).
France’s public authorities have made a significant contribution to supporting this movement: amongst the 34 plans created as part of the New Industrial France strategy (later renamed Industry for the Future Plan, or “Plan Industrie du Futur”) is a plan for wood industries, led by Adivbois, the French Association for the Development of Liveable Wood Buildings, created in 2015 with the aim of promoting construction of high-rise wood buildings within a longer-term objective of sustainable sector-wide development: reducing energy needs, adapting to climate change, alleviating pressure on natural resources, avoiding environmental pollution, innovating and creating jobs for sustainable growth.
In 2016, Adivbois took stock of the current panorama, undertaking a comparative international benchmark study, which revealed France moving into position as a global leader in the field of high-rise wood building construction. More than thirty projects are currently planned in metropolitan areas across France, including those selected from a call for expressions of interest run by Adivbois in 2016 (see interview). “Such a significant number of projects coming to fruition across the world in so short a time (the next five years) really shows what a crucial issue this now is”, explains Marcel Chouraqui, director general of Adivbois.
Highly resistant to fire
Amongst its carpenters, joiners, builders, engineers and architects, France certainly possesses the savoir-faire to meet the challenges of high-rise wood construction. “Although France had lagged behind such places as Switzerland, Canada and the Nordic countries, it has now repositioned itself as a world leader in terms of timber usage strategy in an environment dominated by concrete,” asserts Patrick Molinié. The big players in the construction industry such as Eiffage and de Vinci (already well established in the timber sector with its Arbonis subsidiary) are restructuring in order to respond to this market. For example, Bouygues has launched Bouygues Construction Bois in Ile-de-France and mainstays of the timber industry, such as Mathis, are moving further into general contracting.” In addition, the last decade has seen the emergence of specialist operators such as Techniwood, founded in 2010, and Woodeum, created in 2013, which are developing wood-based technologies to take buildings even higher. These include cross-laminated timber or CLT (a material first developed in 1947 by French engineer Pierre Gauthier), timber frame, and post and beam structures. Woodeum has chosen to use CLT because “its robust structural properties mean that wood panels of up to 20 metres by 3 metres can now be used,” explains Philippe Zivkovic. CLT panels are used for load-bearing walls and floors, although basements must still be made from concrete. CLT also has very good resistance to fire because it does not burn below a temperature of 400°, as well as excellent thermal insulation properties. Hence it generates considerable cost savings compared with heating a concrete building”. Meanwhile, Techniwood offers various technical solutions (CLT, wood framework, and frame) and has invested heavily in research and development. It has developed a material called Panobloc®, a breakthrough innovation comprising cross-fold latticed panels composed of several layers of timber crossed at 90° and shifted. It is effectively a new type of cross-laminated timber: CLTi (the “i” standing for insulation). Panobloc® will be used to build the Silva tower in Bordeaux.
Hyperion – France’s tallest high-rise wood building
The 18-storey Hyperion tower in Bordeaux will rise to a height of 57 metres including 82 apartments assembled as if they were houses around a “vertical street”. It will be constructed using a wooden post and beam structure, with floors and walls made from CLT. This will ensure “mutability of housing and the building’s security,” explains the project’s designer Jean-Paul Viguier & Associates. The building’s central core and first three stories will be made from concrete. On February 7 during a round table event at the ‘Maison de l’architecture d’Ile-de-France’, Jean-Paul Viguier told delegates: “this is not just about one tower made of wood. This project will regenerate the whole neighbourhood of Saint-Jean Belcier, bringing together new retail, residential and office spaces with integrated parking.” He adds: “at the event, we focussed on wood because of its avant-garde aesthetic and artistic qualities, and also because wood undeniably creates a better environment for living.”
In terms of the environment, Hyperion has inaugurated a new generation of exceptionally low-carbon footprint buildings. The lightness and rigidity of solid wood CLT, combined with the robustness of glue-laminated wood and laminated veneer lumber, have provided a means of overcoming the technical challenges of height.