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The Rise of CLT

Jul 13, 2020

The Rise of CLT

In recent years, there has been a growing trend by architects and builders alike to the greater use of exposed timbers and timber for structural strength for construction. 

This rise has come about in tandem with the drive to improved environmental sustainability, and is also due to a rise in technological improvement - namely the development of Cross Laminated Timbers (CLT). These reconstituted timber elements are both attractive and strong, making for a durable, adaptable building material. 
So what does CLT mean for construction and (as far as we are concerned) as importantly, fire rating? In this article we will take a look at: 

  • How CLT is made

  • The strength of CLT

  • The sustainability of CLT

  • Uses of CLT around the world

  • Fire rating CLT

What is CLT?

CLT, which stands for cross laminated timber, is a solid, prefabricated wood panel that comes with exceptional properties. It is strong yet light and has great thermal, fire, seismic, and acoustic performance. As a sustainable building material, it is quick and easy to install, and generates almost zero waste. Because of its low environmental impact and design flexibility, it has become a popular alternative to conventional building materials like steel and concrete.

 

How is CLT made?

Cross laminated timber is made from adhering layers of wood that have been cut from a single log. Each individual layer is orientated in a perpendicular fashion to its adjacent layers. It is then adhered in a symmetrical way so that the layers on the outer side will have the same orientation. Interestingly, CLT products are compiled into odd-numbered layers for superior quality and strength.

The process of gluing together the different layers of wood perpendicular to the layer above and below creates large and thick beams that come close or equal different properties and performance of steel and concrete. But better of all, when coated with fire-resistant paint for wood, CLT helps contribute to a building’s passive fire protection features.

 

How strong is  CLT?

One of CLT’s most innovative properties is its thickness, which lends to its level of strength. This characteristic and many others, has seen a rise in the use of this material as a stand-alone element in new construction across the world (But more on that below). Its sizable dimensions, as well as its versatility and ease in handling, allow for new possibilities in architecture and engineering in the creation of large structures and buildings made out of timber. This makes CLT a high-value alternative to mineral-based construction materials like concrete. When CLT is treated with an intumescent paint for wood, it becomes a good material for both mid and high-rise buildings because of its improved thermal and fire resistance.
In contrast to its strength as a building material, CLT is surprisingly lightweight. This allows for the construction of buildings in locations that would generally not be able to support heavier structures. It can also assist in easing infilling work where a construction site would be difficult to access due to the presence of other buildings.

 

Is using CLT sustainable?

Since it is made from wood, cross laminated timber is a sustainable and renewable building material. With less production requirement than steel the carbon footprint it puts out is significantly less than steel which requires coal and extreme heat for production. But perhaps the most eco-friendly aspect of using CLT as opposed to concrete and steel is the fact that it can help reduce carbon emissions.
Construction and building materials contribute approximately 11 percent of greenhouse gas emissions around the world. The manufacture of concrete and cement is responsible for about 8 percent of emissions. Roughly a ton of CO2 is produced when manufacturing concrete, while steel production emits up to two tons of the gas. Add all of these up and you get a bleak picture of their effects on the environment. However, all these emissions can be greatly minimized through the widespread use of CLT.

 

Uses of CLT around the world

CLT was first developed in Austria during the early 1990s. Its use in residential construction spread throughout Europe in the 2000s in a bid to make the practice more sustainable. However, it had a harder time finding its footing in North America, especially in the United States where stick-frame construction was preferred due to its lower cost. Eventually, architects were inspired to use CLT in bigger buildings as steel or concrete substitutes, and the material began to gain more popularity around 2010.
Today, it is increasingly being used all over the world and the worldwide market for cross laminated timber is projected to grow over the next five years. The major centers of CLT production can be found in Austria and Germany. Europe continues to be the largest consumer of CLT products, but other regions like North America and Asia Pacific are beginning to catch up.
CLT has been used in the construction of several high-rise buildings. Some notable examples include Dalston Lane in the United Kingdom, the Wood Innovation and Design Centre at the University of Northern British Columbia in Canada, the T3 building in the United States, the Tall Timber building in Sweden, and the Mjøstårnet in Norway. And excitingly, in Australia, the tallest hybrid timber tower has just been given the green-light. This will be home to Atlassian’s offices and will be a modern architectural marvel.

 

Fire rating of CLT

Cross laminated timber may be good for the environment and all that, but how does it fare against fire?
Since a CLT panel is a large, compressed, and solid mass of wood, it doesn’t ignite easily. When it’s exposed to fire, its outer layer can still char, but it can be further protected by the application of fire-rated paint for wood. The coating will allow CLT to retain its integrity and withstand even an intense fire for up to 120 minutes.

Is CLT worth it?

Absolutely! As more eco-friendly buildings get constructed, cross laminated timber leads the pack as the material of choice. Its great strength and durability, coupled with its lightness and fire-resistant properties, enable builders to create durable structures without harming the environment.
If you are considering to use CLT in construction but need a good level of fire resistance to it, consult our intumescent experts at Permax.

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