The building industry is constantly changing, regularly benefiting from consistent developments in technology and innovation. One of the most recent developments in the industry is the rise of cross-laminated timber (CLT) as a building material. CLT is created from layers of parallel timber boards laid atop one another in a perpendicular fashion before being glued together. This results in a product that is far more stable than regular timber.
CLT can be used successfully in both residential and commercial projects and while it has been around for the last 20 years, it has not been widely used in the Australian building industry. At AJP Constructions, we are one of the few builders in the country that specialise in CLT, having successfully completed additions to homes in Sydney using the material.
To learn more about the CLT construction process from an engineering perspective, we recently sat down with Damian Hadley, Director at Cantilever Engineers, to chat about the material and how it differs from other types of construction. Keep reading to find out more.
AJP: What are some differences between CLT and brick construction?
DH: Brick construction was perfect back in the day when houses consisted of multiple closed rooms on a regular grid. With today’s architectural expectations of open plan living and high ceilings, brick construction is simply not appropriate. Brick walls also need vertical support at regular intervals to remain sturdy, but CLT has no such requirements; long lengths of wall and double height spaces are exactly the type of construction that suits CLT.
CLT can tolerate a substantial amount of movement, sway and deflection, while brick is a brittle material; even the smallest movement in a building frame can result in brick cracking. This also means CLT is a great choice for building in earthquake prone regions including Sydney.
CLT is also faster to install and can be constructed by a builder with general carpentry skills, while brick construction requires the specialist skills of a bricklayer and is time consuming. More time on site, means more money spent on a build.
AJP: What are some benefits of CLT?
DH: There are many benefits to using CLT, including:
- Reduced construction timelines
- It’s fast and easier to certify
- Structurally, CLT has no height restrictions
- It is an inherently strong structure
- It sequesters a substantial amount of carbon and is therefore a sustainable material
- Building with CLT avoids fossil fuel intensive materials
- It allows for a controlled, precise and consistent build
- Wastage is reduced both during manufacture and on site
- Less disruption to neighbours
AJP: How do you see homeowners benefiting from the use of CLT?
DH: As a homeowner there are two things that can be done to improve efficiency and control costs – reduce the amount of waste going to landfill and reduce time on site. CLT allows for both of these as it involves very little wastage and is quick to install.
Builders can control the amount of time spent on site by having more predictable and accurate builds, which CLT also allows for. As it is prefabricated and delivered to site where it is then pieced together, it only takes minutes to determine if there are any issues, as opposed to days or months. As a machine-made material, CLT is generally quite accurate and if installed with a moderate amount of rigour, its accuracy can be measured within a few millimetres.
AJP: What are the challenges of using CLT and what needs to be considered when using it on your project?
DH: The biggest hurdle is convincing people to use a product they have not used before. Many builders believe there could be hidden risks involved in CLT that may not be worth the effort and that the preplanning may be challenging.
In terms of actually using CLT, installation requires the use of a crane. If there’s no space for a crane or if there are overhead power lines near the site, CLT may not be possible.
Architects and builders will also be required to modify their thinking slightly when using CLT. Processes like insulating and running services in CLT need to be carefully considered as there may be different steps involved, compared to when using traditional materials.
AJP: Would you ever mix systems, for example concrete and CLT in a multi-storey residential build?
DH: Absolutely. A mix of materials can be an ideal structural solution. For example, you could construct a high-rise building with a concrete core, while the remaining portions of the structure could be CLT. A hybrid of steel columns and beams is also a common solution.
In fact, almost every building is a hybrid, a combination of different materials and CLT is no different. It could be as simple as concrete for the foundations and CLT for the rest of the build or a full hybrid of concrete, CLT, steel and masonry. Structurally, it is important not to be locked into using a specific material for the entire build. DIfferent materials offer different advantages and disadvantages, it is more a matter of using the materials wisely and appropriately. The benefit of CLT is that it can be used as a more efficient and cost competitive solution where concrete, steel and masonry would typically have been used.
AJP: CLT is intended to be clad. How can it be left exposed and how is the product affected by being exposed both internally and externally?
DH: The most common question we are asked by architects is “can we expose CLT?” The simple answer is yes, it is possible, but there are restrictions. We generally recommend that CLT is clad.
CLT is usually constructed from lower-quality softwood , which are cross laminated together, which is its main sustainability benefit. It is this lamination process that makes for such a high quality, strong product however, it can have visual defects that you may not want on show. It also means the timber can be easily damaged by everyday wear and tear.
In order for CLT to be left exposed, the cladding must be both durable and visually appealing. This can be achieved by using particular timbers for the external laminate or by treating the external timber, however both of these options may take away from the efficiency of using CLT in the first place.