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Tall Timber

A Study of Tall Wooden Buildings Prompts a Rethink of Fire Protection

Recently, the Fire Protection Research Foundation completed a first-phase hazard assessment related to high-rise timber buildings. We do not yet have a way to evaluate the performance of this new technology, and our work in this area is a fascinating example of how the drive toward environmentally sustainable building design around the world is causing us to rethink some of our fundamental assumptions about fire protection.

Wood-framed construction has been traditionally limited in height and area due to limitations in structural capacity and because of concerns related to the fire safety of this combustible material.

However, a number of innovations in timber products and composite systems have enabled efficient design of taller buildings. These innovations, combined with the view that timber is a sustainable building material, has prompted a renewed look at the prescriptive limits on the use of timber in modern building codes, as well as at the underlying fire safety issues.

The Foundation’s hazard assessment was conducted at the request of the insurance industry. It addresses a review of existing fire safety design guidance, a large body of recent research, fire incidents in timber buildings, and a series of global case studies of both historic and recently built high-rise timber buildings of various construction types. The study, authored by Arup, offers research recommendations to address gaps in knowledge about timber system fire safety performance, and we hope to work with stakeholders to fill those gaps. The report is available online at nfpa.org/foundation.

There is a general comfort level about how we address wood construction in codes and standards. But many of us in North America have never seen a timber building over four stories high, and we are unaware of the portfolio of high-rise timber buildings under construction or in the design phase around the world.

On the surface, this is a fairly typical Foundation project: A new technology emerges, questions arise over the ability of codes and standards to address that technology, and the Foundation assists by providing the technical information needed to inform the provisions of the codes and standards. As we have worked with our technical panel and others on this project, however, I have realised that something is different here.

For starters, wood construction has been with us for a long time, and there is a general comfort level about how we address it in our codes and standards, which generally prescribe a four-story height restriction. But many of us in North America have never seen a timber building over that height, and we are unaware of the portfolio of high-rise timber buildings under construction or in the design phase around the world. Those buildings raise questions about the fundamentals of our comfort level; wooden buildings as tall as ten stories, such as the Forté Building, a residential apartment building constructed of prefabricated cross laminated timber (CLT) panels and concrete floor slabs in Melbourne, are built or under construction, while others with more than 30 stories are being designed. Many of them are in jurisdictions with more restrictive building code environments than our own.

Additionally, the materials used in many of these structures are new to us, and we do not have the information to make accurate evaluations of their performance. Finally, the inclusion of historic high-rise timber structures, like the nine-story Yingxian Pagoda in Shanxi, China, in the portfolio made us realise that some of the other fundamental assumptions that our building codes have historically been based on – compartmentation, sprinklers, and other forms of fire protection – are already changing as construction materials evolve.

With timber buildings, we have an “old” material transformed for use in new structural forms. As we attempt to define the performance we expect from timber in high-rise buildings, we will also gain a more explicit understanding of some of the fundamental assumptions underlying our standards – an extremely valuable process, whether that knowledge is applied to old technologies or new.

If you are interested in phase-two of this project, please contact Amanda Kimball, Research Project Manager at akimball@nfpa.org

Kathleen H. Almand  NFPA Fire Protection Vice President, Research

Kathleen H. Almand
NFPA Fire Protection Vice President, Research

For further information, go to www.nfpa.com

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