What Is Cross Laminated Timber?
Cross Laminated Timber is a generic name given to large structural building panels made from solid wood boards glued together in layers. Like plywood, CLT panels are very strong because the layers of boards run in opposing directions.
The manufacturing process entails taking raw rough-sawn Radiata pine boards from the sawmill and cutting out large knots and other defects which usually makes for reduced lengths. The shorter boards are then finger jointed together into the selected length for their intended CLT panel, then planed on all sides. The planed boards are placed into a press in layers of alternating direction, with glue applied between the layers. Pressure is applied, and after curing, panels are removed from the press and trimmed to exact sizes and edge profiles at a CNC machining centre. They are then ready for delivery to the building site. You can view this process here.
Each panel is custom built to the designer’s specification. Panel size is governed by the press, which measures 15m x 3.5m. Panel thickness depends on the intended load and span. The most common configurations have 3, 5 or 7 layers, with cumulative panel thicknesses between 60mm and 250mm. For full information refer to the Technical section and the XLam Design Guide.
CLT has been widely used in Europe for over 20 years, and in recent years has been gaining ground in North America. The environmental and construction benefits of CLT make it a growth industry, with more manufacturing plants opening each year. XLam was the first CLT manufacturer in the southern hemisphere, and is the only one in Australasia. Later in 2017, XLam will become one of the few manufacturers with more than one CLT plant.
Why Use XLam?
XLam Cross Laminated Timber redefines construction as the new alternative to steel and concrete for Australia and New Zealand.
Why use XLam CLT? Here are six good reasons:
XLam panels are big (up to 15m x 3.5m), and fit together quickly on site. So they make building much faster.
For buildings large and small, XLam panels connect together as a complete engineered wood building solution. Each XLam panel is custom-made to suit the structural needs of the project and required appearance.
XLam panels are manufactured using the latest European CNC machining technology to ensure high precision and eliminate site waste.
XLam CLT is safe. Safe to erect, weighing only 20% as much as concrete. Safe to inhabit, being strong and flexible under load.
XLam CLT is sustainable. Wood stores carbon to help save our planet. And XLam out-performs conventional framed construction in air-tightness, thermal insulation, internal moisture management, acoustic insulation and fire resistance.
For many building types, the XLam construction system out-performs steel and concrete on cost.
XLam’s up-to-the-minute CAD/CAM technology ensures precision and quality control from receipt of the consultant design drawings throughout design and manufacture of the finished product.
Cadworks, the world’s leading specialist 3D-CAD/CAM software, is used to create a 3-D model from supplied plans, and produce workshop drawings. Once approved, these files are imported to Lignocam software which drives the manufacturing process.
XLam’s state-of-the-art German computer-controlled factory machining centres include:
A Grecon finger jointer to glue short boards into long structural lengths.
A Weinig Hydromat planer to dress the lumber for lamination.
Vacuum Pressing from the Swiss company Woodtec.
At the heart of the factory, a Weinmann CNC 5-axis processing centre to shape the glued and pressed CLT panels into to finished sizes and profiles, ready for delivery. The precision of this huge custom-built German processor allows a 15m long CLT panel to be cut to size with millemetric precision.
As a complete building system, CLT is most suited to “honeycomb” construction, ie. buildings whose permanent walls can act as the primary support structure. In this building category apartments, flats, multi-unit housing, hotels, retirement and aged care facilities, schools, and health buildings are all ideal for XLam panels. The CLT walls, floor and roof act together to make a light weight, highly stable and rapidly erected construction system.
Residential floors and roofs
CLT is very economical for residential floors, particularly those on sloping ground where a flat floor platform can be quickly achieved. The span and cantilevering capabilities of CLT permit economies in foundation support. The very rapid installation of a CLT floor creates a solid and safe working base for the builder. XLam floor panels are craned into position at the rate of approximately 100 sq m floor area per hour, meaning an entire house floor can be placed before smoko. This represents a large saving on site labour. Similarly, an XLam structural roof can be placed in the same time and provides immediate weatherproofing and a safe and solid surface for the roofer. Floor and roof panels can be supplied with factory-fixed rigid thermal insulation.
XLam shear walls are much lighter than precast concrete. Provision for post-tensioning can be incorporated in the panel layup. XLam is at the forefront of development in New Zealand seismic resisting construction. See https://vimeo.com/76925854.
Being so light, XLam opens opportunities for the addition of extra storeys to existing buildings without the need for expensive strengthening of structure and foundations.
Building on constrained sites
Just-in-time delivery and the quiet nature of XLam construction (the noisiest tool on site is a power drill) prove very beneficial for building sites with limited space or in sensitive neighbourhoods. Urban intervention projects and remediation of damaged buildings demand public safety and minimised disruption, measures more easily achieved with XLam construction
The fire-resistant XLam AirStair is cheaper and much quicker to install than conventional precast concrete stairs in commercial buildings.
The big cost benefits of XLam:
Lighter building foundations – wood is 20% of the weight of concrete
High accuracy through factory prefabrication, no rework
A smaller site construction team
Fast assembly compresses the building program
Earlier occupancy by user
Shorter term financing requirements
Lower Preliminary and General costs
Faster and progressive access for other trades
Easier fixing of building services to timber
No site waste disposal
Life cycle savings. Building owners and tenants are increasingly concerned with operational costs and sustainability which have become market drivers.
XLam panels fit exactly together on site. Precision speeds up building erection and eliminates time on rectifying discrepancies. Dimensional predictability allows associated building components such as windows and joinery items to be manufactured ahead of time without the need for a site pre-measure.
As well as faster, building in CLT is cleaner, quieter and less disruptive to the neighbourhood. Just-in-time delivery suits projects on tight or awkward construction sites. For residential construction on sloping terrain, a solid working floor plate is efficiently achieved with minimal ground work. Site safety is enhanced. Arrest barriers for joisted solutions are not needed for CLT, so work is more efficient.
Compared with other structural systems, XLam CLT brings a huge advantage to the environment through efficient application of the world’s most sustainable building resource:
Wood stores carbon as the trees grow, and therefore has a negative total carbon footprint.
Unlike concrete and steel, wood has zero “embodied carbon” (ie the amount of carbon used in the process of manufacturing a building product).
CLT is the only ‘carbon positive’ method for long span structures, wherein more carbon dioxide is absorbed through the lifetime of the trees used than is expended through manufacture, delivery and installation.
RMIT University research on Lend Lease’s CLT Forte Apartment building in Melbourne showed the global warming potential of the building materials (cradle to gate) to be 30% less than for an equivalent conventional building.
Site waste is eliminated through digital design and factory prefabrication.
Wood structures can be altered during their life span because they are light and easy to work on to meet changing needs.
The near air-tight nature of CLT construction makes buildings more efficient to heat and reduces energy demand.
In most situations XLam CLT can utilise eco-friendly untreated timber.
XLam CLT is manufactured using a locally grown and sustainably managed wood resource, much of which is harvested within 50km of the factory.
At the end of a building’s life, CLT panels may be disassembled and recycled into new buildings.
Living With Wood
World-wide there is a growing rediscovery of the benefits of using wood and wood products in our living and working environments. These benefits are wide-ranging, real and measurable. Read this informative Australian research report by Planet Ark
Today, wood offers an infinite variety of opportunities for beauty, innovation, ecology, efficiency and adaptability.
Wood has a universal and timeless appeal, outlasting transitory fashions.
Wood gives our surroundings a feeling of welcome, comfort and harmony. It adds warmth and character to spaces.
Wood is hard wearing yet warm to the touch.
Wood is healthy. CLT can improve human comfort by naturally controlling internal humidity and ambient temperature. It buffers variations of indoor humidity by absorbing indoor moisture and releasing it when the humidity drops.
Wood is a good insulator which enhances thermal insulation.
Wood is robust, easy to work with and maintain. Wood structures can be easily adapted and modified to suit changing life needs.
Wood structures are safe. New Zealand’s Canterbury earthquakes proved how well timber buildings perform in extreme seismic events. Today, wood offers an infinite variety of opportunities for beauty, innovation, ecology, efficiency, safety and adaptability.
Wood lives within us, a timeless companion. Take a moment with poet James Richardson.