Should I use CLT or Glulam for my building project?


While we are well known for our glulam (Glue-Laminated Timber) manufacture, we also increasingly use Cross Laminated Timber otherwise known as CLT.

We don’t talk a great deal about our CLT so we thought it would be helpful to share answers to common questions about CLT and how it compares to glulam as a building material.

What is Cross-Laminated Timber?

Cross-Laminated Timber, or CLT, is where you use layers of timber planks arranged at right angles, to create large wooden panels. Typically these measure from around 2.4 metres by 6 metres, but they can sometimes measure up to 12 meters in length, with thickness ranging from 60 to 300 millimetres.

You can read more about CLT here.

How is CLT made?

CLT undergoes a meticulous process. Timber planks are finger-jointed, planed, glued, and stacked into panel shapes. Pressure is then applied usually using a vacuum membrane machine. We don’t currently make CLT in house but import from Austria and Germany.

What is CLT commonly used for?

CLT is a versatile, contemporary, sustainable construction material. It can be used to make any structure where a system of wall, floor or ceiling panels is needed. The panels are almost always delivered to the site with all machining complete, including service holes, door and window openings for example.

CLT finds its place in building roofs, floors, and walls, offering an alternative to traditional structures and stud work but it can also be used as an alternative to timber frame walls, blockwork, and precast concrete planks.

What is the difference between CLT and Glulam?

Like glulam, CLT is made by layering and glueing timber together to create a new product. However, unlike glulam, where boards have their grain running parallel, CLT layers are laid at 90° to each other – hence the term ‘cross’ laminated.

CLT is, in essence, a unique form of glulam, constructed in a slightly different way!

Is CLT sustainable?

Absolutely! CLT, like glulam, is an eco-warrior, using less energy to produce panels compared to concrete, masonry, or steel structures.

Additionally, CLT is like glulam as it acts as a carbon store within your building for the duration of its lifespan.

What are the Benefits of Using CLT?

One of the big advantages of using CLT is the speed of installation – it can be a game-changer. CLT structures can be swiftly erected, thanks to pre-machined panels with doorways, openings, and precise angles. The robust panels can be erected in double quick time – a large-scale flat pack if you will!

Another benefit of using CLT is its strength. Due to CLT panels having a very high strength in two directions, you can use them in a way that can make quite unconventional shell structures and impressive geometries.

CLT can also bring another aesthetic element to a design if you wish – the surface of the CLT is commonly used as a seemless visual timber finish over the inside of the building (you can read more about CLT visual grades and finishes here).

Is CLT expensive?

While the outlay for CLT might be higher initially compared with more traditional methods of construction, the speed of construction and the use of CLT as a visual finish inside the building can often offset the upfront expenses in the long run.

As with all things, it very much depends on what your priority is for your project, but if you’d like a ball park figure we can always help with this.

How long does CLT last?

CLT is built to endure and should last for many decades in the same way that doors or other joinery within a house can last for decades or centuries if they are kept dry.

Vigilance is crucial to prevent water-related issues, as leaks or excessive moisture during installation can pose challenges. With some CLT panels being very large, if a leak appears some distance away water can be soaking into the middle of the CLT and get trapped which can lead to problems later. Equally, it’s important to keep panels as dry as possible by using a membrane and tape joints during installation to stop it from getting too wet. Its also very important to keep the CLT dry during installation, preapplied membranes, end grain sealer and taping of joints on site can help with this.

With proper installation, waterproofing and maintenance, however, CLT can last indefinitely.

When would you recommend CLT over Glulam or vice versa?

CLT and glulam are used for different things normally – most commonly, CLT is used as a panel to make a wall or a floor surface whereas glulam is only usually used as beams to make a frame. Frames which then need to be clad are often clad with CLT, so it is commonly not an either/or choice, rather than which bit where decision as part of your design.

Floor or wall panels can be made from glulam beams laid on their side usually with a tongue and grooved edge. However, we use maximum 600mm wide glulam T&G panels. If you’re making bigger panels the glulam is more likely to warp slightly or get cracks than CLT because CLT is reinforced against cracking by the cross-lamination.

The one thing we would point out is CLT usually needs to be installed with a crane, so if your project is in a space where it is impossible to get mechanical lifting equipment in, it’s best not to specify CLT for internal fit-out. In this case T&G glulam or smaller CLT pieces should be considered.

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Remember, the choice between CLT and Glulam depends on the unique needs of your project, and each brings its own set of advantages. If you’d like to discuss your next project or have questions about CLT, do get in touch and one of the team will be happy to help.