Cross-Laminated Timber – What is it and when does it make sense?
Early in the 1900s, there weren’t what we call “high rise buildings” today, with the 482’ Strasbourg Cathedral being the world’s tallest building. Other than walking, the use of horses and wind sails as forms of transportation were the norm. The world’s population was less than a billion, recording a GDP of what would amount to just over $1 trillion today. 80% of the world’s population lived in poverty, and the lifespan of the average person was about 35 years.
Fast forward two centuries later, the Petronas Towers at 1,483′ was built, development of space shuttles and other means of transportation, the world’s population was over six billion, recording a GDP of over $30 trillion dollars. And less than 20% of the population living in destitution. That said, it is fair to say that there was massive advancement in humanity in those two centuries.
It would interest you to know that amongst the many factors leading to such success, was the change in building materials. Resulting in economically safe buildings. Concrete and novel steel took over the stone and wood construction industry, boasting superiority in almost every aspect, from;
- Strength to weight ratio
- Structural predictability
- Production predictability
- Production replicability, to
- Availability in a variety of shapes and sizes
However, in more recent times, unavoidable natural disasters, recessions, harmful human activities, and the increasing need for a sustainable and greener environment, are presenting engineers with new problems needing new solutions. One of which is the need for greener alternatives to concrete and steel as construction materials.
Wood is the most used building material, especially in the earliest years of humanity. Even though it was replaced by concrete and steel, wood is still the lead building material in most parts of the world, like California, USA. Although wood is tagged as an ancient building material, engineers have found ways to improve wood for modern construction.
Over the last half-century, the building of large wooden structures (Mass Timber) by gluing or fastening wooden members together was slowly becoming the norm. The viability of mass timber was aided by the invention of the Cross-Laminated Timber (CLT) in the mid-90s.
Cross-laminated timber consists of the crossing and gluing the laminae of sawn lumber. It can serve as panelized building components like walls, roofs, and floors. Cross-laminated timber is a special building material because of many advantages, some of which are:
- High axial compression and in-plane shear loads
- Reduced risk of swelling and shrinking
- Quicker construction than concrete and steel, as a result of its size and connectivity
- Fire resistance
- Seismic flexibility
In addition to the slow response of most people to change, concrete and steel dominance has inhibited the acceptance of CLT.
Notably, this is believed to be as a result of the fear that Cross-Laminated Timber will completely replace concrete and steel. This fear is not at all aided by the continuous increase in the number of Mass Timber buildings.
Cross-Laminated Timber buildings are typical of pointing out their advantages over concrete and steel, rather than advantages in cooperation with concrete and steel. That begs the question, will cross-laminated timber perform better in cooperation than alone?
Concrete and Steel
It is common knowledge that concrete and steel perform better together, reaching heights it would not have attained individually. Concrete has a lot of properties that compliments that of steel, some of which include;
- High compression strength
- Moldability on site
- Variability in mix designs and applications
- Fire and moisture resistant (as long as there are no cracks).
Steel, on the other hand, possesses properties that can complement those of concrete as well. Some of which include;
- High structural predictability
- High tensile capacity
Cross-Laminated Timber VS Concrete and Steel
As formidable as the steel and concrete team is, adding a player like CLT, could form an even better team. Let’s look at a few comparisons:
- Completing a CLT is faster than corresponding reinforced concrete and steel buildings, usually between 25% to 75% faster.
- CLT uses a 90% less construction traffic
- The strength to weight ratio of CLT is higher than that of concrete or steel
- CLT suits the growing need for green buildings, more than concrete and steel because it is a renewable material.
CLT has a very high cost and unfamiliarity. However, the cooperation of CLT, with concrete and steel could make up for this problem.
The University of British Columbia’s Brock Commons Residential Hall is a perfect example of combining concrete and CLT. Here, the building’s core is concrete, while the flooring, walls, and columns are CLT. The structure’s properties include;
- Structural rigidity
- Logistic speed
- Construction familiarity
- Seismic flexibility
- Wind resistance
Cross-laminated timber is a very unique construction material with more pros than cons. Causing construction experts to predict the perfect building would be a combination of CLT, concrete, and steel. With the responsibility of floors, shear walls, and roofs falling on CLT.