Over the past decade, the design industry has been increasingly looking toward timber as a building material for the construction of tall buildings. This interest is partly due to the development of new engineered timber products and the potential economic benefits of prefabricated timber elements and composite building systems. However, a recent emphasis on the importance of green and sustainable architecture and an understanding of the potential sustainability benefits of tall timber buildings can be seen as the primary motivator for many architects, owners, governments, and other building stakeholders wanting to design with timber.
SUSTAINABILITY BENEFITS – THE ADVANTAGES OF A TIMBER FRAME BUILDING
Owners, managers, designers, and some government agencies have been placing a greater importance on sustainability in building construction and operation, as buildings are a major contributor to greenhouse gas emissions in their construction and operation.1 This has led to increased interest in the use of timber in buildings, as timber can be considered an attractive material for green building construction.
The use of timber in building construction can positively contribute to sustainable building practices in many ways:
- Timber is considered a renewable resource and the forests supplying timber can offer a natural carbon sink;
- The resource extraction and manufacturing phases of timber products demand a very low amount of energy relative to more conventional structural materials used in construction; and
- Innovative timber systems designed for prefabrication and disassembly allow for reuse of the material and a more resource-efficient product life cycle than typical demolition and down-cycling.
In addition to the sustainability benefits, timber has other positive attributes relative to other building material types:
- Possibility of offsite prefabrication and minimized onsite work allowing for high-quality certified production, independent from weather and a rapid erecting progress;
- Reduction of building weight, resulting in savings in foundation works when compared to other construction materials;
- Ease of alteration onsite; and
- Increased flexibility in architectural design options.
TYPES OF TIMBER BUILDINGS – THE NEXT GENERATION IN TIMBER DESIGN
Timber products, assemblies, and methods of construction have evolved over time. Conventional experience with timber buildings is typically limited to low- and mid-rise residential and commercial buildings. These buildings generally utilize light timber frame construction and are limited in size and open area. This is different from heavy timber frame construction that is increasingly being used for mid- to high-rise residential and commercial applications.
While light and heavy timber framing are used for different applications, the primary differentiator between the construction types is the section size of the timber members used in construction. Although there is currently no universally accepted definition of “light” and “heavy” timber, timber can be considered as heavy where its minimum dimension of solid wood exceeds approximately 80 mm (3”).
In general, light timber frame construction is composed of a greater number of small-section stud members to form wall and floor assemblies, typically enclosed within cladding to form wall or floor framing elements. Light timber frame construction is typically used in low- and mid-rise residential buildings and is often used in buildings up to five- and six-stories, typically above a reinforced concrete ground floor. Framing methods include “platform” and “balloon,” or stick-framed construction.4
Heavy timber frame construction is composed of a lesser number of large-section engineered products to form the building superstructure. While this includes solid sawn lumber sections, modern timber buildings generally use engineered timber products. Relative to solid sawn lumber, engineered timber products offer greater strength and design flexibility and have enabled greater ambitions in architectural and structural design.
The use of heavy timber frame construction allows for greater design flexibility (relative to light timber frame construction) including longer unsupported spans, open-plan areas, and taller construction. The two predominant forms of heavy timber construction include post and beam construction and panelized construction.
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