Building with wood?

Civil construction has a long way to go in terms of sustainability. Every day new alternatives are sought, both in terms of materials and construction techniques. One of the trends that is gaining strength is wood construction – more specifically CLT (Cross Laminated Timber) construction. A more sustainable alternative, considered to have less environmental impact because it is renewable and is in the production chain of carbon dioxide absorption by trees. In addition, its production consumes less energy compared to conventional building materials such as concrete.

The use of wood as a material is not new, but the great innovation is in its ability to be constructed in height, and there are already several buildings around the world with wooden structures (as an alternative to concrete and steel). CLT buildings can reach several tens of floors. For example, the Mjøstårnet building in Norway was completed in 2018 and is currently the tallest wooden building in the world with 18 floors and a height of 85.4 meters. Other examples include the 24-story HoHo Vienna building in Austria and the 14-story Treet building in Norway. In Portugal, there are only a few projects that have used CLT in multi-story buildings. One notable example is the ‘Redbridge School’ building in Campo de Ourique, Lisbon, the tallest Portuguese building constructed mostly of CLT.

Cross Laminated Timber (CLT) is a composite wood solution, usually made from solid wood panels arranged in cross-layers and glued together. Usually, three, five or seven layers are used, depending on the structural needs of the project. This material, by advances in manufacturing technology and in the understanding of its structural properties, already makes it possible to replace traditional materials (concrete and steel) in the construction of multi-story buildings.

There are several advantages to using it:

– Speed of construction: CLT is prefabricated off-site, which allows for faster and more efficient on-site construction. CLT parts are precision manufactured with custom cutting and drilling, which reduces the need for on-site cutting work and speeds up the assembly process.

– Strength and structural performance: CLT is designed for high strength and structural performance. Its cross-layer construction gives the material excellent dimensional stability, stiffness and load capacity. CLT can be used for wall, floor and ceiling structures, and is able to withstand heavy loads and resist seismic forces.

– Thermal and sound insulation: CLT has natural thermal and sound insulation properties due to its layered solid wood structure. This helps reduce heat loss and provides a comfortable and energy-efficient indoor environment. CLT can also be combined with additional insulation to further improve the thermal and acoustic performance of the building.

– Design flexibility: CLT offers design flexibility, allowing the creation of open spaces and customized layouts. The material can be cut into different sizes and shapes, making it easy to adapt to a variety of architectural designs. CLT can also be used in combination with other materials for hybrid design solutions.

– Fire resistance: CLT has good fire resistance due to its predictable response when exposed to high temperatures. As the outer layer is carbonized, it acts as a thermal shield, slowing the spread of fire and maintaining the structural stability of the material.

However, it is important to consider that each project has its own particularities and specific requirements, and it is necessary to carefully evaluate whether CLT is appropriate for the needs and constraints of the project in question.

On the sustainability side, there are also several reasons that make CLT a solution to choose:

– It is a renewable source: CLT is made primarily from wood, which is a renewable and naturally regenerable source. The wood used in CLT comes from sustainably managed forests where new trees are planted to replace the harvested ones, ensuring its continuity.

– Absorbs carbon: During growth, trees absorb carbon dioxide (CO2) from the atmosphere and store it in their fibers. When wood is used in CLT, this carbon remains stored for the lifetime of the material, reducing CO2 emissions into the atmosphere, and helping to decrease a building’s carbon footprint.

– Low energy consumption: CLT production requires less energy compared to the production of other building materials. In addition, the CLT manufacturing process usually takes place in factories, which allows for higher quality control and better energy efficiency compared to on-site construction.

– Less environmental impact: CLT can be manufactured with less waste of materials compared to other building systems. In addition, its manufacturing process generates less greenhouse gas emissions and air pollutants compared to concrete production.

– Allows for dry construction: In addition to the advantages in manufacturing (times, waste and efficiency), the CLT construction method is “dry”, which means that it does not require the use of wet mortar or cement, reducing the use of water, and thus contributing to the conservation of water resources.

– Sustainable life cycle: CLT is durable and can have a long service life. When a CLT building reaches the end of its useful life, the material can be reused, recycled or used for energy production, contributing to the circular economy and minimizing waste.

It is important to note that, although CLT is a sustainable building material, it is necessary to consider the origin of the wood used, preferring certified sources of sustainable forest management, such as the FSC (Forest Stewardship Council) or PEFC (Programme for the Endorsement of Forest Certification) seal. In addition, it is essential to follow best construction practices and consider the overall design and energy efficiency of the building to maximize its sustainable benefits.

Despite all the economic and environmental advantages mentioned, CLT is still used on a small scale. On the one hand, this is a relatively new technology compared to traditional building materials, and lack of knowledge can lead to resistance or lack of confidence in the adoption of this material by construction professionals and project owners. The construction industry tends to be conservative and resistant to adopting new technologies and materials, and tradition and familiarity with conventional building materials may hinder the widespread acceptance and adoption of CLT. This is coupled with a possible perception of higher initial cost compared to traditional materials, even though CLT may offer savings in terms of time and labor during construction. On the other hand, it is important to take into account the limitations not only in terms of regulations and building codes, where the lack of clear guidelines or the need for adaptations in building codes can be obstacles to the more widespread use of this material, but also in terms of limited production and supply capacity, where there is still little capacity to meet demand in many countries or areas.

There has been increased demand for building construction using CLT, but there is still a long way to go. Beelt is committed to reducing the environmental impact of the industry at all stages of the building lifecycle, and takes responsibility for spreading more efficient solutions.