Imagine a material that is efficient, sustainable and renewable. Imagine a material designed with such precision that it can withstand loads of up to 7,000 times its own weight. Just don't look for it among those invented by man. It is the work of nature. It's wood.
Wood is unique. No other natural building material can boast of having been designed from its origin to be so. It is nature that has designed it for us, that manufactures it. And already at its origin, it fulfills the same structural function with which we usually use it in our buildings.
Wood is the skeleton of trees. Therefore, it responds primarily to a constructive function as the structural one. The wood is the support manager of the tree to remain standing, in charge of resisting its own weight and the onslaught of the wind.
It plays another crucial role, as it transports the sap that feeds the tree. This is why wood hollows out. It results in an improvement of the material, as it gives it some of the properties that make it more suitable for construction: light and resistant. Not in vain, it has been meticulously designed by nature under a strict Economics of resources. It achieves maximum results with minimum expenses.
Wood is more flexible than other structural materials, and its strength is also lower. However, given its lightness, this is an advantage. It is when comparing the stiffness and strength of the various structural materials with their weight that wood demonstrates its optimum design. Its specific stiffness is already similar, not less. But the differential fact is its specific resistance, where it wins (and by far). It is four times higher than that of steel, and forty times higher than that of concrete. Only very light alloys, such as aluminum, or highly technological materials, such as carbon fiber, provide similar specific strengths. This is the reason why, at the origin of aviation, these (such as Howard Hughes' Spruce Goose, the longest aircraft in history - 97.5 m) were built with wood.
It is not surprising, therefore, that wood is one of the first building materials used by man. Our ancestors discovered its magnificent structural properties and began to use it as a lintel in their doors and as a covering for their houses. Its light weight made it easy to handle, and it was widely used. It was the necessary and indispensable support for the construction of arches and vaults, and later protected them from the rain.
In the 20th century, modernity brought other materials, and the knowledge treasured in tradition seemed to be relegated to oblivion. Today, it is once again an appreciated and valued building material.
One might think that this rediscovery of wood is due to ecological and environmental criteria. Wood is a natural material that absorbs CO2, and therefore contributes to decarbonization (as politicians like to say nowadays). Moreover, it is renewable and inexhaustible, as it is produced in forests. Although there are bad examples that remind us of the danger of decimating them, there are many forests that have been cared for for centuries, in which the balance between forest use and the environment has been maintained. Current forestry certifications (such as FSC or PEFC) guarantee not only the proper origin of the wood, but, more importantly, the sustainability of the forest where it grows and of the society that cares for it.
Let's not kid ourselves: the reason is not ecological. As is almost always the case in industrial sectors, the explanation is simpler. If buildings equivalent to those made with other materials could not be constructed, their leave ecological footprint would not matter. Forget romanticism. The reasons that have driven this change are purely economic and efficiency, based on the innate properties of this material already mentioned: lightness, efficiency, resistance.
Modern wood construction bears little resemblance to traditional carpentry, to the elaborate assemblies developed by generations of experienced carpentry craftsmen. In the last decades, an intense work of standardization and improvement of the scientific knowledge has been developed at area. And, above all, new products and techniques have been designed especially adapted to the needs of today's construction.
We can use a simile to explain this. Think of the Swedish furniture company IKEA, business . Surely you are familiar with it, and probably even own some of its products. If it has crossed borders, it is because it has surpassed the traditional furniture industry in many aspects. Its flat packs, the simplicity of assembly, its quality standards, the result of intense industrialization, are the seed of its success. It has applied modern techniques and concepts to a traditional industry.
Something similar has happened in the wood construction industry. It no longer has little in the way of traditional, artisan techniques. One example is the cross-laminated panel, CLT, manager , which is largely responsible for the current success of wood construction. This panel is made from layers of boards glued together, with each layer rotated 90 Degrees with respect to the previous one. This peculiar arrangement improves its dimensional stability and structural properties. The result is a multipurpose element, which can be used as a wall to support vertical loads in its plane, or as a slab for bending loads.
Although in reality, as in the case of IKEA, the great revolution is not in the product, but in the system. It brings to fruition what has been learned from past experiences in prefabrication and industrial manufacturing. It uses parallel developments from other industries, such as the most advanced fasteners, the digital design , or numerical control manufacturing. This results in a fast, precise and simple construction. The panels arrive on site already cut to their exact size and shape, and very few people are needed to put them in place and join them by simply screwing them together. This simple assembly allows the construction to progress very quickly and with great precision. As the products arrive on site prefabricated, performance is improved and the production process is simplified. The savings are even greater, because being a dry construction is also gaining a lot of time by not having to wait for the setting of the wet elements.
The eight floors of the world's first CLT building ushered in a new paradigm and set an example for future developments. Built in 2008 in London, Murray Grove's timber frame structure was constructed by just five Austrian carpenters in just eight weeks, at a rate of one storey per week. It was this greater speed that convinced the developer to test the system, for instead of the usual two years for a standard building, the timber process took just one year.
Obviously, wooden buildings are lighter. The most obvious impact is that the foundation is substantially reduced. But it is not the only one, because lighter buildings also behave better in the event of earthquakes. It is therefore not surprising that in countries with a high seismic threat, such as Japan, their building tradition makes extensive use of wood. Also, lighter buildings save a lot of transportation costs. Related emissions are reduced, as are traffic jams and neighborhood nuisances.
There's even more. You don't just save on construction. Not only do you get Structures safe and reliable in shorter times. Wood buildings are also more energy efficient. Building with wood saves energy. It does so during production, because much less is required to work it and bring it to the construction site. And during the life of the building, since it consumes less because it is better insulated. And the fact is that wood is a magnificent natural insulator. Together with modern techniques, it is relatively easy to construct a building with reduced consumption, in accordance with current demands.
Returning to IKEA, perhaps the reader is unaware that it also manufactures houses (furnished with its products) through its subsidiary BoKlok. These are modular homes, which are built in just under two months at a very competitive price. Needless to say, they are obviously made of wood.
Let's not forget: the merit belongs to nature, which gives us such a fascinating material as wood. We remain mere apprentices. Mjøstarnet, a hotel in the Norwegian town of Brumunddal, is currently the world's tallest building made of wood. But its 85.4 meters are dwarfed by the world's tallest tree, the 116-meter-tall American sequoia Hyperion, which is 30 meters taller. Let's keep learning.
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José Manuel Cabrero
Director of Chair Madera, University of Navarra.
partner of Eurocode 5, design of Structures Wood.
