Cross Laminated Timber (CLT)
CLT, tilt up timber, pre-cast timber panels, 'jumbo' ply
Cross Laminated Timber (CLT) is the engineered wood of the future and is making the construction of entire buildings from timber a reality. First developed in Switzerland in the 1970s, CLT is an extension of the technology that began with plywood and may be best described as a 'jumbo plywood'.
Having gained popularity in Europe, CLT - also referred to as 'tilt up timber' or 'pre-cast timber panels' - is slowly being adopted more widely as a viable alternative to more traditional building practices.
Layers of timber, known as lamellas, are glued together with the grain alternating at 90 degree angles for each layer. The exterior layers' grains run lengthways, giving optimum strength. CLT is manufactured in a similar way to glulam, except that glulam is layered with the grain.
Cross-laminating layers of wood veneer improves the structural properties of wood by distributing the along-the-grain strength of wood in both directions, and this means that CLT panels can be used to form complete floors, walls and roofs.
While CLT is a timber product, it should not be thought of as a timber frame product - it is a timber panel product that actually has similar characteristics to that of a pre-cast concrete panel. The advantages this offers new buildings is quite exciting - timber panels are much lighter than concrete, more easily worked and easier to erect.
The potential of CLT as a sustainable building material is only just being realised around the globe.
CLT is available in Europe and has only recently entered the North American market. In 2017 work commenced on a manufacturing plant in Australia, there are also CLT importers serving the Australian market. You'll find some of these in the Supplier section of WoodSolutions.
Framed timber buildings, of post and beam or stud and joist construction, resist lateral loads (wind, earthquake or impact) by using rigid frames (portals), braced frames (trusses and cross-bracing) or structural sheathing elements (diaphragms).
Diaphragms are an efficient structural solution to resist lateral forces. The sheeting materials that are generally used as lining or cladding can usually be upgraded to resist shear loads, easily and economically. The framing then performs dual functions, resisting both horizontal and vertical loads.
In cases where diaphragms comprise structural sheathing, additional design efficiencies can be incorporated to resist loads normal to walls, floor and roofs using the composite stressed skin action developed between the sheathing and the timber frame.
The advantages of timber shear walls and diaphragms include:
- architectural design freedom (curves, cantilevers, clear spans)
- lightweight construction
- high impact load resistance
- resilience (no brittle cracks)
- fast conventional construction
In this section you'll find information about the design and construction details of timber framed diaphragms (both horizontal and vertical) used in domestic, low rise commercial and industrial buildings.
Framing design for dead loads, or dead and live loads acting normal to the framing are covered in AS 1720.1 Timber Structures and AS 1684 Residential timber-framed construction. To develop efficient diaphragm action, some adjustments, particularly connection details, are usually required.
Information about diaphragm materials and systems is included, however the majority of the design and construction details provided herein are for structural plywood diaphragms for which documented design information is available.