In the 19th Century it was steel. Then later, in the 20th Century concrete rose to prominence. Now in the 21st Century, wood is the rising star of the building industry, for its low carbon footprint and renewable resource attributes. To truly build Eco Cities of the future, many of the materials used today will eventually be swapped for more renewable resources. Wood, specifically engineered wood, is already making strides in large buildings today.
The use of wood for tall building construction is not a novel idea. In fact, the five story Horyu-ji pagoda in Japan is over 1500 years-old. Today, the increasing number of code-approved, engineered wood construction projects are reaching five, six and even ten, stories in Europe and Australia. CREE by Rhomberg has two buildings in Austria, its global headquarters called the LifeCycle Tower ONE and the IZM Montafon, set to be one of the largest tall timber buildings in Europe by area.
Two main types of engineered wood products dominating the tall wood building race today are Cross Laminated and Glued Laminated Timber (glulam). These “engineered” wood products combine smaller sections of wood into larger posts, beams and mass timber panels. These wood products are strong and rigid enough to replace steel and concrete as structural elements in large buildings, even up to 30 stories.
As timber is a carbon storage mechanism, buildings built primarily from wood inherently have a low carbon footprint. With proper forest management, trees and their timber can be a sustainable, renewable resource. One aspect of managing sustainable forests is to replace old and damaged trees with young ones, which grow faster and absorb more carbon from the atmosphere. Older trees, absorb less carbon and if allowed to die all the carbon they stored is released back into the air or ground. It therefore makes sense to sustainability harvest forests and produce engineered lumber and other wood products to store carbon.
While most tall buildings are still built using on-site processes, one firm has developed a prefabricated, systemized timber based approach. [pagebreak]Cree by Rhomberg and it’s U.S. division, CREE Buildings, combines glulam posts and beams with a limited amount of concrete and steel to manufacture structural wall and floor components. This system approach enables architects to design stunning wood buildings up to 30 stories and for each one to be uniquely different.
Research shows the CREE LifeCycleTower (LCT) system requires 50 percent shorter construction times and 39 percent fewer resources over the life of a building. The LCT system can also substantially reduce the amount of concrete used in construction, resulting in a lighter structure, with a smaller foundation and up to 90 percent lower CO2 emissions. While the LCT ONE in Austria is eight stories, research shows the CREE building system has the ability to support as many as 30 stories.
The CREE LCT system works by building wall and floor components from glulam posts and beams.The floors slabs are a hybrid of timber and concrete, optimizing the benefits of both to meet all the structural, fire and acoustic requirements. CREE manufactures the wall and floor components off-site, under a controlled environment, where wasteful and costly mistakes can be contained and do not slow down on-site construction.
Meanwhile, on site, the foundation of a building is laid and the stiffening core is erected. The core contains the elevators and stairs and provides interior support for the hybrid wood/concrete floors. While wood is the optimal choice as a material for the core, concrete and steel can also be used. Since the components are prefabricated off site, the shell construction can go up as quickly as a story a day once the foundation and core are complete (time lapse video).
During fire, steel buildings can collapse without warning once high temperatures are reached. Conversely, wood burns predictably at a constant rate of approximately 1.5 inches per hour. [pagebreak]Therefore the size of a wood structural member can be increased accordingly for fire protection. This additional thickness is referred to as the charring layer of timber.Specifically, the CREE wood/concrete hybridslabs, with the additional charing layer, have been tested and passed a two hour fire test in a full sized fire chamber.
As global sentiment pushes to reduce excessive use of materials and decrease global CO2 levels, wood is slated to gain mainstream exposure as the ideal building material for tall buildings. These tall wood buildings are revolutionizing skylines, revitalizing local timber industries and ushering in a sustainability renaissance in all aspects of building, from architecture to carpentry. It’s certainly an exciting time to be an architect.
Nabih Tahan is VP of Business Development for CREE Buildings Inc.
Rhomberg, H. Bonomo, J. The Natural Change in Urban Architecture. Cree GmbH. 2010