Cross-Laminated Timber CLT
Cross-laminated timber, or CLT, is one of today’s most exciting structural materials for medium-rise buildings. Light and strong, it is ideal for off-site engineering, resulting in spectacularly short build times using less on-site labour. When you add in the sustainability benefits of this super low carbon construction method and the health and comfort that come from living or working in a building whose structure is natural and hygroscopic, it’s little surprise to see so many exemplar CLT buildings going up in the US, Canada, Australia and Europe.
Some, like the Stadthaus in Murray Grove, Hackney are entirely constructed from pre-fabricated solid timber CLT panels, from the load-bearing walls and floor slabs, to the stairs and lift cores.
Others, such as Patch 22’s new housing development in North Amsterdam use a hybrid approach of CLT panels, glulam beams and concrete.
And some are dreams of the skyscrapers of the future, such as this vision of a 62-storey structure.
The range of CLT panels commonly available
CLT is normally manufactured in panels from 80 to 300mm thick, although it can be available in panels as thin as 60mm and as thick as 500mm. Panels are manufactured in widths from 1,200 to 3,000mm (or even 4,800mm to special order). Panels are normally manufactured to a maximum length of 16m, although lengths of up to 30m can be produced. Typical walls for 5-6 storey developments are usually 100-140mm thick, but long span floors without intermediate beams are easily achieved by using 240-280mm panels (dependent on loading conditions).
Construction with CLT
Cross laminated timber (CLT) panels are typically prefabricated and delivered to site as large structural elements, reducing crane loads and speeding up the erection programme. The panels are installed without the need for wet trades, using a crane and lightweight power tools. Site storage is reduced by just-in-time delivery scheduling, and health and safety issues are minimised due to the product’s light weight and the speed of erection.
CLT results in a significant reduction in the overall self-weight of a structure, which often leads to lower groundwork costs. Wall construction thickness can be reduced to gain space within the structure. Slim floor construction can also be achieved.
CLT wall panels can be used as shear walls, while floor panels can be used as diaphragms. The large bearing area of CLT means panels deliver an extremely high axial load capacity, with a high shear strength to resist horizontal loads. The early provision of a watertight structure allows other trades to start earlier. First fix items are installed directly to the surface – or, if details are known at the manufacturing stage, channels can be formed in the factory.
CLT and BIM
Manufacturers can work with all BIM files for manufacture, and usually use IFC format for the co-ordination of this. The CNC machines produce to 1-2mm tolerance, and so whatever is in the BIM model is exactly what’s produced to mm accuracy. The manufacture model can also be fed back into the BIM process to check for clash detection, movement of windows / doors etc. throughout the design process.
CLT – Want to learn more?
Why not further your CLT knowledge here on Wood Campus by visiting HERE.