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Render de la torre de 350 metros prevista para el año 2041 en Tokyo. Imagen © Sumitomo Forestry.
Empire State of Wood
Empire State of Wood, Metsä Wood. Imagen cortesía de Michael Green Architecture

For years, architects and the construction industry have been willing to design and construct the wooden buildings we still see today, but they could not escape from a very small market niche. \Some projects by a few daring architects, with strange shapes that in most cases bore little relation to what people expected of a building, were relegated to specialized bio-architecture publications or those of the wood sector itself.

Today, however something has changed

Wooden tower project in Bordeaux by Sou Fujimoto and Laisné Roussel. Image © Sou Fujimoto Architects, Laisné Roussel, Rendering Tàmas Fisher And Morph

It is true to say that some technical advances have been achieved. This rapidly expanding sector is devoting a numerous resources to research into developing systems with ever greater capabilities. These advances and the growing use of a construction system based on the use of CLT contra-laminated panels have made it possible to make a quantum leap in the size of wooden buildings, and the race is on to construct the “tallest wooden building in…” with an impact in the media, even mainstream media, a trend that is undoubtedly favourable for the spread of these structures.

It is also a fact that the new generations of designers are more familiar with this material and know more about it. Erasmus courses and internships in countries where the tradition of wooden constructions is much better established than in Spain, together with the proliferation of master’s degrees in sustainable architecture, have meant that, in the years of the last financial crisis, many young architects hoping to find for a job built up the sensitivity and technical knowledge base necessary to come up with and design these buildings.

All this untapped potential required a final and fundamental element, demand. And demand, as often happens, follows the dynamics of fashion, in other words, what is perceived as suitable, right and timely at any given moment. Wood’s time appears to have come, and hopefully it is here to stay, as the benefits of its proper use in the construction sector are undoubtedly positive for the planet and its inhabitants.

So now, wooden building projects are to be found in the most prominent architectural magazines, not only in specialized magazines .

Vancouver Art Gallery Project by Herzog & de Meuron. Image © Herzog & de Meuron

The demand no longer comes exclusively from the private sector engaged in the self-build housing development, which remains the main market segment, but also from the public sector and large companies. In Hondarribia (Basque Country), the state-owned company Visesa is building 65 publicly subsidised homes within the largest block of wooden houses in Spain,which will be surpassed by “La Comunidad Habitacional“, “, a project by the architects of the firm Cierto Studio, which won the international competition for the Glòries block, commissioned by Barcelona City Council to build almost 300 units of social housing. The group La Borda is constructing Spain’s tallest wooden building in Barcelona, a co-housing project on a use assignment basis which will rise 25.5 metres over a site owned by the local council. In addition, the Ábaton architectural firm is developing the tallest wooden building in Madrid in the El Viso neighbourhood.

Proyecto ‘La Comunitat Habitacional’ de Cierto Estudio. Imagen © Cierto Estudio

Outside Spain, the 18 floors of the Brock Commons Tallwood House building in Vancouver (Canada) make it the tallest wooden building in the world, while the Japanese Sumitomo Forestry company is planning to build a tower made of this material set to reach a height of 350 metres to celebrate its 350th anniversary in 2041. In Toronto, Google, through Sidewalk Labs, one of its group companies, is developing a project for an entire neighbourhood built of wood in the Quayside, initiative on the shores of Lake Ontario. Back in Japan, the next Olympic Games will be held in 2020 in Tokyo’s new stadium made using a wooden structure, designed by Japanese architect Kengo Kuma, famous for his wooden building projects. These are some examples of the current state of the art of these kinds of constructions, which are beginning to appear all over the world.

Brock Commons Tallwood House, Vancouver (Canada). Photo Michael Elkan, courtesy of Acton Ostry Architects and the University of British Columbia

Beyond their formal characteristics, which blend perfectly into the current aesthetic sensibility, wooden constructions have multiple benefits, which we can group together in four main categories:
– Environmental sustainability
– Energy savings
– Living comfort
– Rationalization of the construction process

Project for the New Olympic Stadium in Tokyo. Image © Taisei Corporation, Azusa Sekkei Co., Ltd. and Kengo Kuma and JV Associates, courtesy of the Japan Sport Council via Architecture of the Games

Environmental sustainability

Building is one of the human activities with the greatest impact on the environment.
During its life cycle, from its construction to its demolition, a building consumes natural resources, produces emissions into the environment and generates waste. Several LCA (Life Cycle Assessment) studies compare the life cycles of buildings made with different construction systems based on wood, reinforced concrete, steel and brick, and demonstrate that the impacts of buildings made of wood are more sustainable for the environment.

Comparison of the impacts of one building made of reinforced concrete and another made of wood. Source, publication ISSN 2075-5309, Adam B. Robertson 1, Frank C. F. Lam and Raymond J. Cole

These analyses are very complex and take into account a large number of aspects. Among them are some that lead to wooden buildings achieving a higher sustainability index.
Wood is a material whose CO2 balance (a greenhouse gas) is zero. As they grow, trees trap CO2 from the atmosphere, storing it until it is eventually burned and returns into the atmosphere. Wood is a renewable material. Environmental regulations require that the number of trees planted must always be higher than the number of felled trees, and the PEFC and FSC certifications for wood provide a guarantee of the origin of the wood from forests with controlled felling. Wood is not a natural resource at risk of depletion, unlike sand. Wood is a recyclable material which allows the implementation of circular economy strategies within the territory.
In Spain, the planned management of forests means it is under-exploited, so much so that the vast majority of structural timber has to be imported from other European countries. Even so, its use remains favourable with respect to non-recyclable materials.

Illustration of the analysis of the life cycle of a building. Courtesy of LeTourneau University Civil Engineering for Sustainability

Energy savings

It has been calculated that buildings consume around 40% of the energy required in the world. The energy efficiency of buildings is, therefore, extremely important for the fate of our planet and energy savings are undoubtedly making significant changes to the way we build. Technical regulations require increasingly efficient systems. In Europe, Directive 2010/31/EU (updated by Directive 2018/844/UE ) requires that buildings will have to have nZEB (nearly Zero Energy Building) energy consumption by 31 December 2020 or, if they are owned by public authorities, by 31 December 2018.
To achieve a nearly zero energy balance in a building, it is essential to reduce the thermal flows as much as possible through its envelope, improving the insulating power of the cladding and eliminating any thermal bridges. Wood’s low thermal conductivity (λ, W/m·K) enables us to achieve low values of thermal transmittance in the elements of the envelope (U, W/m2K) with lower thicknesses of thermal insulation and easily reduce the thermal bridges which occur at the intersections of the structural elements and in the geometrical changes of the envelope. At the same time, it is easier to avoid problems of interstitial condensation.
Its favourable characteristics for thermal insulation have meant that this material has traditionally been widely used in countries with cold climates.

Comparison of thermal conductivity in brick, concrete and wood

In areas with warm climates, such as the Mediterranean climate in much of Spain , the need for insulation in winter is combined with the need for protection against high temperatures in summer, the latter being sometimes more important. The high thermal inertia of the building (a long lag and a high degree of thermal damping) is essential to achieve this without wasting energy.
High-density materials allow us to achieve more favourable lag and thermal damping values and, in this regard, wood is not the most suitable because it is a light material. Construction systems using wood therefore have to be adapted to our latitudes. It is no coincidence that traditional Mediterranean architecture typically employs thick stone and brick walls. Structures which use contra-laminated panels, solid elements with a significant mass, are more appropriate than those made of wooden beams and columns. The use of massive elements in the interior of the building and the position and type of thermal insulation are fundamental for the optimum performance of the building in summer.
However, we can build a building with high energy efficiency made of wood in Spain too, thus capitalizing on all the benefits of using this material in its construction.

Forest House by Pep Ferrer, Marià Castelló architects, made with CLT panels on the island of Formentera. Photo © Marià Castelló Martínez.

Living comfort

Living comfort is defined as the psychophysical well-being of people living in an environment, and it is a feeling which chiefly depends on certain environmental conditions, most of which are measurable and controllable (temperature, humidity, interior air quality, air speed, surface temperature, lighting, acoustic conditions, etc.).
We can highlight just some of the characteristics of wood enabling us to control these variables and achieve the appropriate values to ensure a high degree of comfort.
Wood is a hygroscopic material which tends to absorb or lose water, depending on the environmental conditions. It is, therefore, a regulator of internal relative humidity and, at the same time, it acts as a filter of the internal air penetrating the micro-ducts that make up the fibres of the material. Thanks to its low thermal diffusivity, the wood’s temperature varies slowly when it comes into contact with a body at a different temperature. The thermal sensation is pleasant to touch, because it reflects our thermal state. Hence, we usually regard wood as a “warm” material.
Wood is a natural material and the sensation of being in contact with nature has important psychophysical benefits.

Rendering of the 350-metre-high tower planned for 2041 in Tokyo. Image © Sumitomo Forestry.

Optimization of the construction process

One of the main advantages of wooden construction systems is the possibility of pre-fabricating most of the building elements, including some of the fittings and finishes. The assembly of the elements is performed dry during the work, with the consequent water savings. The times for completion are noticeably reduced, allowing, significant economic savings and major mitigation of the impact of the work on the surrounding area.