Initially produced in Austria for the purpose of using less valuable timber, cross laminated timber (CLT) has progressively gained ground worldwide due to its possibilities in terms of quality, durability, reliability and safety of the constructions, not forgetting its minor impact on the environment.

Although the eco-efficiency of cement and concrete is talked about nowadays, the bottom line is that their energy efficiency, durability and recyclability, waste production, energy consumption, carbon dioxide (CO2) emissions and natural resource consumption are still a cause for concern, not only during the construction phase but also later when the buildings are being used.

Cross laminated timber is produced from certified sustainable forest wood, the production of which entails a lower energy consumption than that of concrete or steel, which makes it an excellent measure towards cutting carbon emissions and the use of fossil fuel.

Wood is a natural, renewable and recyclable resource. Wood absorbs CO2 during its growth by fixing carbon for the formation of organic matter, and thus contributing to prevent the greenhouse effect. It should be noted that the CO2 fixed by the tree, by the wood, is only released into the atmosphere when burned. Therefore, felling, processing and recycling operations never release that CO2 into the atmosphere. In other words, wood, and as consequence, timber constructions, operate as batteries storing carbon dioxide storage batteries. The CLT panels are prefabricated, produced in factories, and for this reason generate lower waste on-site compared to other construction materials used in civil construction. It is also possible to reuse parts or segments derived from cutting the panels, such as openings for doors and windows, in different applications or substructures like staircases or other architectural elements.

Initially produced in Austria for the purpose of using less valuable timber, cross laminated timber (CLT) has progressively gained ground worldwide due to its possibilities in terms of quality, durability, reliability and safety of the constructions, not forgetting its minor impact on the environment. Although the eco-efficiency of cement and concrete is talked about nowadays, the bottom line is that their energy efficiency, durability and recyclability, waste production, energy consumption, carbon dioxide (CO2) emissions and natural resource consumption are still a cause for concern, not only during the construction phase but also later when the buildings are being used. Cross laminated timber is produced from certified sustainable forest wood, the production of which entails a lower energy consumption than that of concrete or steel, which makes it an excellent measure towards cutting carbon emissions and the use of fossil fuel. Wood is a natural, renewable and recyclable resource.

As this is the project phase of longest duration, any delays that might occur will be related to lack of knowledge of the product’s potentialities and mechanical properties. There are so many possibilities of use that, as the knowledge level progressively increases during the project phase, there may be a higher number of reviews in design and coordination, which could delay the production phase.

With a resistance comparable to that of concrete, CLT is five times lighter, meaning that when applied to buildings, this helps to reduce the scale of the foundations and the effect of seismic action.

With high durability, excellent thermal, acoustic and electrical insulation, the texture and colour of CLT makes it an aesthetically attractive material.

Regarding regulations, the standard regulating CLT production (EN 16351) [2] was issued in 2014, with a revised version of Eurocode 5 soon to be released that will include this innovative wood derivative. In Portugal, the licensing for this type of house operates in the same way as for a conventional house made of concrete or masonry.

The construction project of a CLT house is associated with different options and phases, from its design, throughout all the work’s planning and execution, up to the phase of its use and operation. Although the project planning phase may require more effort because everything is decided and predetermined in the factory, with all the openings for doors, windows already cut with high precision, the actual construction work and assembly phase are remarkably fast. As this involves industrialised structures, with high structural rigidity, the margin of error (about 2 mm) is very small. It is possible to assemble a 200 m² house in 5 days, just with teams of three to five people. This large-size manufacturing precision gives the builders a high degree of confidence in the product during the construction phase and other suppliers of supplementary materials to confidently prefabricate components required for the construction. As this is the project phase of longest duration, any delays that might occur will be related to lack of knowledge of the product’s potentialities and mechanical properties. There are so many possibilities of use that, as the knowledge level progressively increases during the project phase, there may be a higher number of reviews in design and coordination, which could delay the production phase. With a resistance comparable to that of concrete, CLT is five times lighter, meaning that when applied to buildings, this helps to reduce the scale of the foundations and the effect of seismic action. With high durability, excellent thermal, acoustic and electrical insulation, the texture and colour of CLT makes it an aesthetically attractive material. Regarding regulations, the standard regulating CLT production (EN 16351) [2] was issued in 2014, with a revised version of Eurocode 5 soon to be released that will include this innovative wood derivative. In Portugal, the licensing for this type of house operates in the same way as for a conventional house made of concrete or masonry.

Although there may be a higher cost related to transport and assembly, the construction costs of CLT panels are competitive compared to steel and concrete construction costs. The labour required to erect the structures is lower and the worksite time is substantially lesser. Most of the volume of work is carried out in the factory, in other words, in a controlled environment, for delivery to the implementation site as structures ready for use that merely need to be assembled. This also enables the capacity to accurately estimate the costs of all the project phases before their implementation.