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Laminated timber: is CLT the solution to the change?

el 26 February, 2019

Get to know laminated timber or CLT is an almost impossible task when you try to investigate their properties, definition or characteristics just because you will find information that is extremely technical and which language is intended for experts.

In order to solve this difficulty and make the information accessible to the public, we spoke with Amaya Álvarez del Río, an architect who in 2016 conducted a research on laminated wood called  “El panel de madera contralaminada. Cerramiento ecoeficiente en España” (“The laminated timber panel. Eco-efficient enclosure in Spain”). In the research, she analysed how laminated timber emerged, what it is and its level of sustainability and efficiency through an analysis of the environmental impact during the life cycle enclosures.

 

  • After you’ve done your research, what would you say laminated timber is?

CLT panels placed in structure

My research work deals with laminated timber (CLT) as an eco-efficient enclosure in an architectural project.

Based on this, I would define it as a constructive and structural material that plays the main role in an envelope.

It is important to clarify that by envelope, we are not only referring to facades, but also about roofs and floors.

 

 

 

 

 

  • Why is it important to incorporate wood into construction?

In addition to have indications of good structural qualities, thermal behavior, seismic, etc., the results achieved after the research work show that it is also important due to the high sustainability and energy efficiency during its entire life cycle compared to conventional systems (brick, and concrete).

The conclusions of the study were, for example, that the wood system in the production phase is much more sustainable due to the predominant use of a natural material whose industrial process is not very intense. In addition, it acts as a CO2 sink during the growth phase and makes the amount of CO2 emissions be negative. If we compare the construction phase, the brick and the concrete pollute abundantly because they are “in situ” construction. Meanwhile, the contralaminate system is based on prefabrication, so that all the elements arrive at the construction site finished, and only need to be placed in position by cranes, saving time and costs.

Finally, in relation to the end of their useful life, the enclosures that compose the building are mostly recyclable, being able to form constructive systems of “closed cycle or cyclic” due to their prefabricated and versatile condition, while the others have a very poor recyclability.

 

  • Why is it not so common built with wood today?

This is a matter of different materials evolution. During the last century, traditional construction was dominated by materials such as brick, concrete and steel, which suffered a remarkable development in their manufacturing techniques and construction, adapting to new times. These offered more advantages and possibilities than timber construction. Gradually, at the end of the twentieth century, wood was developed increasingly, until the CLT was born among other systems.

Infographics with historical dates of the CLT

Thus, we first obtained a product on a structural scale and, finally, a prefabricated element with sustainability criteria, able to compete with the rest of the materials and offer unique characteristics and aspects..

 

  • In your opinion, does CLT have more advantages than disadvantages or vice-versa?

Although in my opinion the multiple qualities offered by the CLT prevail, from the point of view of sustainability and efficiency the most negative aspect (especially in our country) is the little (commercial) development in wood construction systems compared to conventional systems. As a result, the current investment in the forest industry is insufficient to support a high demand for wood products.


In addition, forests would also be unable to be sustainable and develop forestry, as deforestation would be much higher than the renewal of the forest cover to close the sustainably cycle.

 

  • One of the deficiencies of wood according to some experts is fire resistance, was this factor taken into account in your study?

As I have already commented, my study is based on the eco-efficient qualities of the CLT system, so this factor was not taken into account in the analysis. But in the research process, I came to the conclusion that wood, despite what is thought, has good fire resistance. This is due to the creation of a carbon layer on their perimeter that acts as an insulator and prevents that the carbonization of the wood reaches the nucleus, which would maintain its mechanical properties intact. To do this, slightly increasing the cross-section of the pillar, beam or wall would significantly increase its resistance to fire.

The surface exposed to fire burns and creates a carbonized layer that protects the interior of the beam or pillar.

This behaviour in structures is measured in function of the evacuation time that offers before it collapses, therefore, if we compared it with steel and concrete, wood is a suitable alternative.

In order to appreciate it in a more visual way, we include a video where the test was carried out.

 

 

 

 

 

The Rescue College of the Estonian Academy of Security Sciences conducted a fire resistance test in November 2017. The experiment attempted to find a solution to the existing conflict over the burning of wood. It was a building constructed with CLT panels produced by the Arcwood timber company and there were large wood surfaces inside exposed to fire. The conclusion of the experiment was that, despite the fact that wood catches fire easily, CLT panels have a high fire resistance due to their size and the way they are built.

 

 

  • Which is the future trend of wood? Will it eventually be incorporated into construction?

Step by step the development is greater, especially in northern European countries. This is due to the rise of the “green movement” in construction, the improvement in the efficiency of the CLT technique, its homologation as a product and an optimization of marketing and distribution chains.

If the timber construction sector continues to develop and grow, it would involvea greater economic interest in the sector, with the consequent investment. This would also mean the development of sustainable forestry and a greater attention to the maintenance of forests, thus avoiding deforestation. In my opinion, the use of wood in Spain will be increasingly standardised as a construction option, as it is beginning to be seen in the residential sector or in small modular projects.

 

“Laminated wood has an advantage over the rest: store CO2”.


Laminated wood or CLT is a fully viable alternative as has been demonstrated in countries such as Finland, Austria and Denmark. However, in Spain the CLT is not being promoted, among other things due to the lack of means for a sustainable development of our forests, that is, to create areas that allow us to plant trees without producing deforestation and to solve the massive felling.  The most favourable solution for all parties is to promote a new sector that would benefit not only the creation of jobs, but also the care of forests and natural parks.

 

On the other hand, despite existing discrepancies with fire resistance as its main disadvantage (due to misinformation), laminated wood has an advantage over the rest: store CO2 by acting as a natural sink. In other words, it absorbs and stores it, reducing carbon dioxide emissions. This reduced impact of CO2 is an essential aspect nowadays, because every day more and more people are trying to act against climate change and the transfer to this type of construction can be one of the solutions to this problem.

Laminated timber: is CLT the solution to the change?

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