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Cross-Laminated Timber (CLT) was first developed in the early 1990s in Austria and Germany and has been gaining popularity in residential and non-residential applications, mainly in Europe. Currently, panels are being manufactured in a limited number of places in North America, which allows CLT to be used in a few projects while trade organizations and governmental agencies adopt specifications and codes for its use. CLT is being used in Europe as the structural system for eight and nine story buildings with proposals up to seventeen stories. CLT is an engineered wood product consisting of glue laminated wood boards, approximately 20-60mm (.79” - 2.36”) in thickness, with each layer set at right angles to the next layer. This cross lamination creates panels, ranging from a 3-layer 57mm (2.24”) panel to as thick as an 11-layer 300mm (11.8”) panel, which can span in two directions and be used for load-bearing walls and spans. Cross-Laminated Timber (CLT) has both positive and negative attributes. The most positive attributes include seismic response and sustainability. CLT performs extremely well seismic events. There have been shake table test done on 5-7 story buildings using the same settings as record seismic events. In all cases, the building survived completely, and would need minor repairs to be re-occupied. Wood structures have a significantly lower embodied energy and associated carbon emissions than equivalent steel and concrete structural systems. Wood is also a carbon sink, removing carbon dioxide from the atmosphere and storing it in building components. There is also the increased construction speed and reduced amount of labor on site. An eight story CLT building in London, had the structure completely assembled in 29 days by four carpenters. One of the potential barriers to using CLT as a structural system is its nature of being a solid wall system. This means the systems that typically hid inside a wall cavity will now need extra attention in their integration with the structure. Since the product is made up of wood, this requires special consideration in construction as well as fire protection. The system is unable to get wet during construction so measures to protect it from the elements are necessary. Timber is self-protecting in the sense that it will char on the outside, preventing heat build-up at the center and allowing it to retain its strength during exposure to fire. CLT panels are designed to resist fire by calculating charring rates.
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