Wood is a bet by engineers around the world to reduce the carbon footprint of buildings

In an age of steel and concrete, the Pagoda, a structure built at Japanese Buddhist temples, is a reminder of the long history of wood as a building material. New techniques are showing that wood can now be used to build even taller buildings, some of which have already been built in cities around the world.

The 14-story Treet apartment complex in Bergen, Norway, is currently the tallest. But the 18-story Brock Commons wooden dormitory at the University of British Columbia in Canada will be completed in 2017. That is also the expected date for construction on the Alto in Amsterdam. Arup, the consultancy working on the project, says it will be built from sustainable European pine. Some architects have already begun drawing up designs for the timber. Tratoppen, a 40-story residential tower still in the design phase in Stockholm, is one of them.

Wood has many attractive features as a building material, in addition to its aesthetic qualities. A wooden building weighs almost a quarter of the weight of an equivalent structure made of reinforced concrete. This means that the foundations can be smaller.

Wood is a sustainable material and a natural “storehouse” of CO2. Trees absorb carbon from the atmosphere, which is then stored within the structure of the building. Large concrete and steel constructions, on the other hand, tend to leave a huge carbon footprint. The main reason is the manufacture of the material needed to support them. Using wood can reduce your carbon footprint by 60 to 75 percent, according to some studies. There are two main challenges in using wood for large-scale construction. The first is whether it is strong enough. In recent years, major engineering advances have been made in engineered wood, and we now have a few options. One of these is cross-laminated timber (CLT), which is made from layers of wood glued together with their fibers interlocked at right angles. While processes such as carbon fiber composite alignment make vehicles more resistant, CLT makes structures much more rigid, as indicatedinternational studies.

According to Edward Borgstein, from Mitsidi, there is another important point: the need to acquire good raw material. This means that it is essential to use beams made using wood with a quality and origin certificate, such as the FSC – Forest Stewardship Council – internationally recognized for verifying compliance with environmental and socioeconomic issues of forests. Furthermore, as with any change in construction practices, it is essential that employees undergo training to become accustomed to handling the material and producing quality work.

In addition to improving the sustainability of the project, the use of wood opens up a range of new architectural possibilities, with the use of different construction forms, prefabrication and structures with exposed finishes.

For example, a recent experiment carried out by the architecture firm Skidmore, Owings & Merrill and Oregon State University shows how resistant manufactured wood can be. The researchers obtained a hybrid form of laminated wood with concrete connections. It consists of an 11-meter CLT beam with a thin layer of reinforced concrete spread over the surface. Thicker layers of concrete were placed in places where the floor is supported by pillars.

The structure was placed in a large test rig and pressed by a powerful hydraulic press. The researchers knew how the structure would behave under pressure, but they designed the experiment to find its limits. The floor finally began to crack when the load reached 37,200 kg. This is almost eight times the load value for the quality of the structure that was designed.

The concrete was initially placed over the floor only for sound insulation. But it ultimately helps to deal with the second biggest concern of using wood: fire. The concrete adds a layer of fire protection between the floors.

Usually a large mass of wood, such as CLT flooring, is difficult to burn without a constant source of heat. This is the same reason why it is difficult to light a fire when all you have is tree trunks. The outside of the material chars, which prevents the inside of the wood from starting to burn.

Large urban fires in the past, such as the Great Fire of London, were almost entirely caused by smaller wood fires that reduced the intensity of the fire and spread to larger buildings. Today, thanks to fire-resistant coatings and modern sprinkler systems, large timber buildings can withstand most fires, says Benton Johnson, who led the project with Skidmore, Owings & Merrill.

Johnson says the tests show that not only can timber be made strong enough for construction, but that “it makes a lot of sense to use it for that purpose”. Although a cubic metre of concrete is cheaper than an equivalent volume of timber, there are specific gains in construction time. He believes that timber’s appeal, both visually and in terms of sustainability, will make it a commercially attractive material for property developers.

But what about termites and rot? “If left unchecked, both steel and concrete can lose their load-bearing capacity as quickly as timber,” says Michael Ramage, director of the Centre for Natural Material Innovation at the University of Cambridge. Dr Ramage and his colleagues are currently testing the use of timber in large-scale construction, including an 80-storey skyscraper that has been presented as a concept study in London. If built, it would be the second-tallest building in London, behind the 95-storey Shard. For a busy city like London, there are even more advantages to building taller buildings with timber, Dr Ramage adds. For starters, the construction site would be much quieter without the heavy construction machinery and plant, instructions for laying deep foundations, pouring concrete and installing steelwork. There would also be less construction-related vehicle traffic. For every truckload of timber, it would take five more to transport the same amount of concrete and steel. All of these factors are reflected in the total cost of construction: a wooden building can be much cheaper. Anders Berensson, the architect who designed Tratoppen, believes that using manufactured wood for construction will be the cheapest way to develop large buildings in the future. Another benefit of the material, says Berensson, is the ability to easily carve details into the wood. In his current project, the number of each floor will be carved into the exterior of the building. A major obstacle to this renaissance of wood is the law, after all, building legislation varies around the world. In the United States, for example, cities can have wooden buildings of only five or six floors. Of course, approaches can be taken, and supporters of wood believe that as more constructions made with the material increase, the laws will be adjusted to the new reality. In Brazil, the reality of building regulations based on non-standard codes and predominantly prescriptive regulations make it difficult to use wood as a building material. However, the most recent changes in standardization via performance criteria open new paths for the use of wood construction systems. The new Building and Construction Code of the Municipality of São Paulo, recently approved, removes the maximum height limit of 8 meters for two-story wooden buildings, which was included in its 1992 version.

It is important to note, however, that simply using sustainable materials in construction does not guarantee that a building will also be sustainable during its operational phase. Tests must be carried out during the design phase to improve energy performance and comfort for the end user, and to identify opportunities for optimization through an Integrated Design process.

Source: The Economist