Recently, Vancouver architect, Michael Green, issued a report entitled Tall Wood, arguing that skyscrapers and other tall buildings should use more wood as a primary construction material. His argument is that wood is up to the task, is less polluting, and is more environmentally sustainable than the materials currently used. Green’s (2012) buildings would employ “massive timber” elements such as cross laminated timber, laminated strand lumber, and laminated veneer lumber. Green is not suggesting that these tall building be of wood only. Rather, he is arguing that mass timber be integrated with other commonly-used structural materials such as concrete and steel.
While wood and wood-mix skyscrapers capture the imagination, extending the height of buildings with the more typical lighter-frame construction is perhaps a more practical concern. Currently, light frame construction tends to be limited to buildings of four storeys and less in North America. In some jurisdictions, this limit is mandated by building codes: in others, it is simply practice. Yet, the ability to construct acceptably safe timber structures with appropriate sprinkler and other technologies led Switzerland to change its fire codes in 2005 and allow the use of structural timber in medium-rise residential buildings of up to six storeys (Frangi and Fontana, 2010). Depending upon the application, mid-sized wood frame buildings can be a less expensive and more flexible alternative to other structures.
Despite the prevalence of wood frame structures throughout North America and parts of Europe, major concerns remain over the fire safety of such structures. This paper discusses some of the issues relating to wood structures and flammability.
It can be observed from this review that most fire safety provisions are similar in nature, whether the Chinese, Canadian or American provisions are applied. However, the Chinese code seems to be slightly more restrictive than the North American building codes with respect to wood-use allowances.
Over the past 10-15 years a renaissance in wood architecture has occurred with the development of new wood building systems and design strategies, elevating wood from a predominantly single-family residential idiom to a rival of concrete and steel construction for a variety of building types, including high rises. This new solid wood architecture offers unparalleled environmental as well as construction and aesthetic benefits, and is of growing importance for professionals and academics involved in green design.
Fire safety is widely perceived as a barrier to implementation of tall timber buildings, particularly for engineered mass timber buildings with significant areas of exposed timber and timber structural framing. This negative perception is exacerbated by a lack of scientific data or experimental evidence on a range of potentially important issues that must be properly understood to undertake rational, performance-based engineering design of such structures. With the goal of delivering fully engineered structural fire designs, this paper presents and discusses a framework for using scientific knowledge, along with fire engineering tools and methods, to enable the design of timber buildings such that, when subject to real fire loads, their performance is quantified. The steps in this framework are discussed with reference to the available literature, in an effort to highlight areas where additional knowledge and tools are needed.
As timber buildings are constructed taller, architects and building owners are asking for more timber to be exposed. Addressing how exposed timber and in particular cross laminated timber, influences a fully developed fire through to self-extinguishment is a current and complex fire safety issue. There is limited research available on how exposed timber alters heat release rate, temperatures and fire duration. This paper provides a summary of the relevant research to understand similarities in findings and how the results of fire tests can be applied. Research shows that large areas of exposed timber has a significant impact on heat release rate, but limited areas of exposed timber can be accommodated within a fire safe design. The location of exposed timber and avoiding two or more adjacent exposed surfaces, is an important finding. It is evident from the limited testing that a single exposed timber wall of approximately 20% of the total wall area has little impact on a compartment fire. The development of a calculation methodology to account for the change in compartment fire dynamics when two or more surfaces are exposed is the next step in the advancement of exposed timber fire safety engineering.
The development and renaissance of modern engineered products, advanced connections and modern construction technology have made it viable to design and construct multi-storey timber buildings. However, a number of issues need to be raised urgently, in particular fire safety and secondary structural effects. This research aims to...
Sustainable, safe, durable, cost-effective and efficient; wood is used across Canada in occupancy classes such as business, residential, commercial and assembly. In the United States, many mixed-use buildings have been designed as “podium” buildings; a wood structure bearing on a podium of noncombustible construction. The International Building Code includes provisions that allow wood buildings, often housing residential or business occupancies, to be constructed over a podium of noncombustible construction accommodating mercantile or assembly occupancies.
The concept of a horizontal fire separation, acting to a certain degree as a “horizontal firewall”, was introduced in the International Building Code in the mid-2000s, allowing the podium to be considered a separate and distinct building from the wood structure that sits overtop. Since podium structures are becoming increasingly “à la mode” in the construction industry, integrating the horizontal fire separation concept into the National Building Code of Canada would allow the industry to benefit from the advantages of wood construction in mixed-use buildings
At the request of FPInnovations, this technical report has been prepared as a guideline for the implementation of design provisions for wood podium buildings into the National Building Code of Canada. Various strategies, special considerations, and possible risks for fire safety in this type of building are explored.
Model building codes in the United States limit timber construction to six stories, due to concerns over fire safety and structural performance. With new timber technologies, tall timber buildings are now being planned for construction. The process for building approval for a building constructed above the code height limits with a timber load-bearing structure, is by an alternative engineering means. Engineering solutions are required to be developed to document and prove equivalent performance to a code compliant structure, where approval is based on substantive consultation and documentation. Architects in the US are also pushing the boundaries and requesting load-bearing timber be exposed and not fully encapsulated in fire rated gypsum drywall. This provides an opportunity for the application of recent fire research on exposed timber to be applied, and existing methods of analyzing the impact of fire on engineered timber structures to be developed further. This paper provides an overview of the performance based fire safety engineering required for building approval and also describes the engineering methodologies that can be utilized to address specific exposed load-bearing timber issues; concealed connections for glulam beams; and the methodology to address areas of exposed timber.
This article provides an overview of the code requirements pertinent to large cross-laminated timber (CLT) buildings and the methods for meeting the requirements in Canada. Canadian building codes are objective-based. Compliance with the code is achieved by directly applying the acceptable solutions up to certain prescriptive building sizes (height and area) or by developing alternative solutions beyond the height and area limits. The fire safety design for a CLT building larger than the prescriptive limit must demonstrate that the building will achieve at least the minimum level of performance afforded by noncombustible construction in limiting the structural involvement in fire and contribution to the growth and spread of fire during the time required for occupant evacuation and emergency responses.
Multistory buildings using mass timber and cross-laminated timber (CLT) as the primary structural elements are being planned and constructed globally, with interest starting to gather momentum in the United States. Model building codes in the United States limit timber construction to a building height of 85 ft (25.9 m) because of concerns over fire safety and structural performance. Up to 85 ft, the mass timber can be exposed. Architects and developers in the United States are pushing boundaries, requesting mass timber structures are constructed as high-rises and that load-bearing mass timber such as CLT be exposed and not fully protected. This provides an opportunity for the application of recent fire research and fire testing on exposed CLT to be applied, and existing methods of analyzing the impact of fire on engineered timber structures to be developed further. Fire testing has shown that exposing large areas of CLT significantly impacts the heat release rate and fire duration. This article provides an overview of the code requirements for timber construction in the United States, provides methods for building approval for a high-rise timber structure, and summarizes recent CLT compartment fire testing that is informing the fire engineering process. Methods for solutions are also discussed.
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