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Cross-Laminated Timber vs. Glue-Laminated Timber

13 minutes
April 23rd, 2021

What is Cross-Laminated Timber?

CLT (Cross-Laminated Timber) is when layers of timber cut from a single log are glued together symmetrically, with the grain of each outer layer alternated at 90-degree angles. The most common method is to use an odd number of layers that are glued together in the same orientation.

This process was first developed in Austria and Germany in the 1990s. Gerhard Schickhofer, an Austrian researcher, greatly contributed to the research into cross-laminated timber. CLT experienced a boom in usage throughout the whole of Europe by the early 2000s and hasn’t slowed down since.

Can Cross-Laminated Timber be Used Outside?

Cross-laminated timber is not the best choice for exterior applications, especially when used as external cladding material. This is because CLT is not designed to be exposed or used in exterior environments due to being sensitive to moisture. This is why cross-laminated timber must be protected from sources of moisture such as rain.

What is Glue-Laminated Timber?

As a popular choice when it comes to engineered wood products, glulam (Glue-Laminated Timber) is when laminates are bonded and glued together. This process is done by layering each laminate with the grain, which results in producing larger and longer length members.

Glulam also has a long and rich history. It is widely accepted that glulam was first used all the way back in 1842 in the Holy Trinity church in England. In fact, the King Edward VI College had glulam roof structures constructed in 1866 which are still standing today.

However, internal stresses in the wood would lead to detachment issues over time that plagued many construction projects. To address this issue, resin glue was invented in 1928. It provided an affordable and waterproof alternative with a high adhesive strength that was also much easier to use.

Can Glue-Laminated Timber be Used Outside?

There are many grades and species of glue-laminated timber which are widely used for both interior and exterior applications. For outdoor applications, GLT timber systems such as MASSLAM are most commonly used for outdoor structural purposes including roofing, beams and external columns.

What are the Main Uses of Glulam?

Glulam is used in a wide variety of applications due to its versatile, superior strength and durability qualities such as:

  • Flooring – Glue-laminated timber is an ideal material for flooring as it showcases the natural beauty, strength and warm colours of the timber. It is used as flooring across many applications including industrial, domestic and commercial.
  • Portal Frames – Due to its impressive strength and flexibility, Glulam is used in projects that require interior spaces free of columns with large spans.
  • Roof Trusses – Historically used as ceilings in cathedrals, GLT can be painted, oiled, decorated and stained to create an aesthetically pleasing roof framework.
  • Exterior Balustrades & Rails – Glulam is a great choice for exterior applications such as rails and balustrades. This is because Glulam is usually built from durable and treated hardwood and softwoods, providing impressive strength and durability to external environments.

What's the Difference Between CLT & GLT?

The key difference between both is their strength properties.

Because cross-laminated timber is made by alternating each layer at 90-degrees, its strength goes in two directions. The direction that has the highest number of layers is the strongest point, whereas the weakest point relates to the direction with the least amount of layers.

The difference with glulam is that is it constructed with all of its layers oriented towards the same direction. This means all its strength goes in one direction, making it ideal for support structures such as trusses, columns and beams.

How Much Stronger is Glulam?

The laminating process for GLT makes it perfect for applications requiring heavier loads, complex shapes and longer spans than reinforced steel and concrete. In terms of strength, Glulam timber is one-sixth the weight of concrete and one-tenth the weight of steel, and is stronger than steel due to its greater stiffness and strength.

However, when it comes to a majority of mass timber projects, CLT and glulam are both used during construction in order to take full advantage of their benefits.

RMIT Garden Building – Glulam made from ASH’s structural grade Victorian ash

What are the Benefits of Using CLT?

There are many benefits of using CLT for construction. These can include:

  • Strength and uniformity of properties.
  • Reduced assembly time and labour.
  • Fire-resistant.
  • Sound absorption.
  • Insulating properties.
  • High aesthetic quality.
  • Is lighter than concrete.
  • Is easy to erect.
  • Highly sustainable building material.
  • Similar characteristics to pre-cast concrete.

What are the Benefits of Using Glulam?

There are even more benefits to using glulam, which include:

  • Stronger than solid timber.
  • Straight and curved members for design and architectural benefit.
  • Large section and long length sizes.
  • A high degree of dimensional stability.
  • Structural capabilities.
  • Fire-resistant.
  • Easy to erect and install.
  • Sustainable.
  • Great sound absorption qualities.
  • Increased construction speed.
  • Can save between 5-25% of building costs.
  • One of the best Life Cycle Assessments of all building materials.

Which is Better?

CLT and glulam can go hand in hand. Glulam beams with a post ‘grid’ offer many open plan design options for applications such as offices and commercial buildings. In these scenarios, laminated hardwood beams and posts are used as supporting grids that incorporate CLT or glulam floor members.

So, which is better? Well, the advantage of using glulam over CLT is that the open plan of a grid system allows partition walls to be constructed and/or removed when required. Best of all, glulam is cheaper to construct because it has less volume than timber. The ‘honeycomb’ CLT systems are commonly used as load-bearing walls and are fixed in position to create a closed-plan design.

Now don’t get us wrong, CLT and glulam are both sustainable, strong and viable options for mass timber construction. However, glulam allows the flexibility of different shapes and the ability to change a space, whereas CLT offers a static system.

But when it comes to knowing which one is best suited to your project, it will largely depend on the design and building structure.

Ballantyne Street – Glulam created from ASH’s Victorian ash structural grade

The Future of CLT & Glulam

The mass timber construction industry is on the rise in Australia and we are seeing more architects and engineers embrace mass timber options. Existing buildings include:

  • Barangaroo International Building Sydney – Glulam and CLT
  • RMIT Garden Building – Victorian Ash Glulam Beams
  • Latrobe Regional Gallery – Victorian Ash Glulam
  • Public Library Docklands – Glulam and CLT
  • Deakin Trade Training Centre – Victorian Ash Glulam
  • Marist College Bendigo – Victorian Ash Glulam
  • Melbourne Zoo (Predator Precinct) – Glulam
  • And the list goes on…

With many industry professionals opting for mass timber, it will be exciting to watch the development of this inspiring industry.

Find Out More About Glulam

ASH has an entire glulam product range called MASSLAM which caters to mass glue-laminated beams. We have also serviced many projects including the RMIT Garden Building and the Latrobe Regional Gallery. MASSLAM column and beams are sustainable, strong, affordable and fire-resistant – ideal for your next project.

Find out how we can help your next project get off the ground by contacting us below.

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