The 5 myths about cross laminated timber (CLT)

Developed in Europe, glue laminated timber (glulam) and cross laminated timber (CLT) emerged as an evolution of solid wood, being considered the construction material of the 21st century.

Building structures in lighter materials such as wood can raise some doubts not only in relation to resistance, but also concerning their durability and necessary maintenance. Being a material that enables constructions systems of large structural capacity by using large-scale panels that promote prefabricated construction, there are various myths and misunderstandings about CLT which we would like to address.

The 5 Myths

If built correctly and in conformity with the construction regulations, wood has a better performance than any other system, and be constructed completely hermetically. In contrast to standard solid wood, that when exposed to high temperatures shows a large protective char layer, cross laminated timber panels, when exposed to fire, inhibit its propagation, and show a low speed or charring rate. Due to its low surface area, even without any coating, CLT panels inhibit the fire from spreading, encapsulating the flame in a restricted area and limiting its development.

Another major attribute of CLT is its solid thermal mass and conductivity, meaning that, if one side of the panel is exposed to 1000 degrees Celsius, the other side will remain at ambient temperature due to its low thermal diffusivity.

The entire production process of CLT is highly industrialised, taking place in a factory, under detailed planning, where the members (panels) produced are virtually perfect, with residual error margins. The installation plan supplied by the manufacturer offers easy and fast handling, in due to the high level of prefabrication. Although they can be very large, a conventional installation team with experience in panels can easily lift, place and screw CLT panels. In fact, compared to traditional construction processes, the number of workers required to erect a CLT construction is much lower than those required to implement civil construction work with heavy construction materials, and of lower dimensions.

CLT panels are produced from wood that grows in sustainably managed forests. By enhancing the value of forestry products, we are caring for and protecting our forest. Perhaps this explains why the developed countries of Central and Northern Europe have a larger swathe of forests as a consequence of the higher value given to wood in their construction systems used in housing.

Wood is the only construction material that grows naturally and is renewable. In fact, over the last 50 years, less than 2% of the inventory of standing trees in the USA has been harvested each year, while the net growth of trees has been 3%.

CLT is an alternative to traditional construction, treasuring sustainable and efficient construction, able to store carbon dioxide, boosting forest renewal, which is why it is a key factor in environmental conservation.

If we consider the total value of a system not using CLT, it is extremely competitive in relation to the costs of other slab construction materials. But it is also necessary to consider all the added-value benefits:

The installation cost is substantially cheaper, which enables considerable savings, namely a 50% cost reduction compared to the installation of other materials.

• As it is a material of low weight but high structural rigidity, wood structures, despite their large size, will weigh less than half the weight of other types of structures, leading to cost-cutting related to the foundations required to support the structures.

• Safety at the workplace is drastically increased due to the CLT panels being prefabricated, and normally the only electric tools are pneumatic screwdrivers.

CLT constructions give rise to a combination of resistance, ductility and low weight, comprising the ideal system to resist earthquakes. Seismic testing assure superior structural resistance and safety, especially due to its excellent mechanical properties. In Japan, a large 7-storey building was submitted to rigorous seismic tests, simulating 10 earthquakes of different intensities, having remained intact.

More than replacing construction in traditional systems, or civil construction in its “modus operandi”, CLT panels seek to offer versatile and sustainable alternatives to supplement timber solutions, simultaneously offering a suitable alternative to various applications that currently use concrete and steel.

This is a recent construction system with demonstrated benefits concerning thermal, acoustic, anti-fire and anti-seismic protection, proved in specific assurance and quality tests. An efficient solution, of high structural rigidity, with clear benefits to the environment.