Is CLT the Architectural Solution to the Building Demands of the 21st Century?
I recently had the opportunity to visit the Nordic Factory in Quebec, Canada. Nordic is one of the leading producers of CLT, or cross-laminated wood, an engineered wood product which is commonly referred to as mass timber.
Watching as this material has gained popularity over the past number of years, particularly in Europe, we’ve become very excited by its potential. Right now there’s a substantial amount of buzz around CLT and it has been described as ‘the material of the 21st century.’Being a shameless building science nerd, I was particularly excited about this visit. During my tour of the Nordic Factory I learned first-hand about what goes on behind the scenes to produce CLT. To greatly simplify the process – there are five basic steps:
When the trees first come into the factory, they are scanned by a 3D scanner, which in a matter of seconds determines the most efficient cutting pattern to get the maximum yield from each individual piece.
Next, the log is cut into several strips of timber, these are then finger-jointed at the end and glued together to create incredibly long stretches of wood.
These lengthy batons are laid beside each other, a thin layer of glue is applied and a second layer of perpendicular members is placed on top.
This process is repeated, layer by layer to create huge panels which can measure up to 64′ long by 8′ wide and 15″ thick. The build-up is then compressed in a massive press.
Architects and construction teams can submit their CAD or BIM files and automated machinery will cut the individual pieces to order.
What inspired me the most about my visit to the Nordic Factory was their focus on creating a sustainable product and their forest management practices. The Nordic Factory currently grows over two million acres of black spruce trees. However, only 1% of the acreage is harvested. As a result, this factory has created a net positive cycle of tree growth. Harvested areas grow back into a forest that is naturally regenerated and restored to its original ecological makeup. Even when trees are harvested, nothing goes to waste, with every part of the tree being utilized.
Using cross-laminated timber as the main ingredient in a building design has many benefits. Compared to steel or concrete CLT is reasonably easy to work with on site. Prefabricated sections arrive on a truck, are quickly craned into place, and are simply joined together with a skeleton crew. It has been said that if you see someone with a saw or a hammer on a CLT building site – it means something has gone wrong.
Of course when it comes to timber building – there is always the question of fire-safety, but CLT is vastly different from stick-frame wood construction. Mass timber is significantly more difficult to ignite and once it catches fire it begins to char, causing it to burn at a slow predictable rate. Believe it or not, engineered timber like this can outperform structural steel in a fire. In one test, a glulam beam was pitted against a steel beam in a fire. The steel failed after 30 minutes, while the timber remained straight and true, retaining 70% of its structural integrity. On top of all this – CLT is made of a renewable crop, making it one of the most sustainable and low carbon building materials on the market.
In this ASTM regulated fire test the steel beam collapsed after 30mins, while the Glulam retained over 70% of its strength.
Of course it isn’t all plain sailing designing with CLT. As with all new materials it will require a huge amount of rigorous testing before it will be widely accepted by building departments around the world. In addition to this CLT is unfamiliar terrain for many designers, so working with it requires the development of new details and ways of building.
Despite these challenges, mass timber represents a fantastic opportunity for the construction industry. The world’s population is both growing and urbanizing rapidly. This means more, buildings, denser buildings, more steel, more concrete and more carbon emissions. According to Canadian architect Michael Green, who is well-known for his use of CLT, steel and concrete combined represent 8% of the total greenhouse emissions. The building industry contributes 47% of the United States’ CO2 emissions. In his TED Talk, Michael makes a strong case as to why we should be building skyscrapers from wood.
We believe that it’s time that we look to alternative materials to meet the building demands of the 21st century. But we also have an urgent duty to decrease carbon emissions and unsustainable building practices. CLT provides a perfect solution for this complex issue. It’s sustainable, low-energy, and carbon negative, and it allows architects to dream, design, and build bigger!