High Rise Timber Can Withstand Fire Hazards

Thursday, April 23rd, 2015
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While the use of timber materials in multi-storey buildings has been a perennial source of safety concerns due to their combustible nature and associated fire risks, new construction solutions may have made such fears redundant, paving the way for the increased usage of wood in high-rise structures.

Robert Gerard, fire engineer with Arup, noted that engineers have already developed techniques for the usage of wood as a safe and reliable construction material in multi-storey buildings.

 Robert Gerard

Robert Gerard

“The solutions already exist to create safe, multi-storey timber structures,” he said.

Gerard, who will be sharing his expertise on timber building solutions at the Frame Australia Conference and Exhibition on engineered wood construction systems in June, is the co-author of Fire Safety Challenges of Tall Wood Buildings, a report released in December 2013 that was commissioned by the USA’s National Fire Protection Association (NFPA) to explore the potential of timber as a safe and sustainable building material in high-rises.

According to the report, it is possible to confer both light and heavy timber frames with enhanced fire resistance via the addition of at least one layer of rigid, non-combustible gypsum board, thus providing  protection to the underlying wood and delaying the onset of combustion.

This technique, referred to as “encapsulation,” is an easy and practical means of achieving fire safety, and entails little more than the attachment of non-combustible gypsum board to the timber frames by means of nails or screws.

Fire safety can be further improved by incorporating additives into the gypsum board that increase its resistance to heat and inhibit combustibility.

The report also points out that heavy timber frames, which are those most commonly employed for the columns, posts and beams of larger structures, already possess an inherent level of fire resistance, given the charring properties of timber.

This charring process occurs at a steady and predictable rate during the exposure of timber to high heat levels, and results in the creation of an insulating layer that delays heat increases at the core.

[Diagram of charring cross-section

Diagram of charring cross-section

“From an engineering perspective, taking advantage of the charring behavior of wood is another means of enhancing the fire safety of timber building materials,” said Gerard.

Engineered forms of wood that employ this charring propensity to enhance fire safety are already available under a variety of names, including cross laminated timber (CLT), laminated veneer lumber (LVL) and glued laminated timber (Glulam).

The ability to use timber more safely and extensively in high-rise structures promises to dramatically improve the sustainability of the construction sector, given that wood is the ultimate form of renewable green building material.

While the solutions for safe usage already exist, public awareness of their potential continues to lag, as is so frequently the case with the development of fresh approaches and technologies in professional spheres.

Gerard nonetheless noted that a shift is already taking place in the global building sector when it comes to high-rise timber.

The UK, Scandinavia and Germany are leading efforts to foster the usage of wood as a building material for multi-storey buildings, starting with gradual increases in the height restrictions for timber structures.

The US, Canada and Australia remain slightly behind, continuing to impose prescriptive height caps on wooden buildings.

Changes in these jurisdictions would appear to be well on their way, with the commissioning of the NFPA report over a year ago itself a sign of rising awareness of the potential impact of these advances in building techniques.

Toward the end of last year Forest and Wood Products Australia (FWPA) issued a call for amendments to the National Construction Code (NCC) that would permit the development of timber buildings as high as 25 metres.

Australia is already host to the world’s tallest timber apartment complex, Melbourne’s 10-storey Forté, which was built to a height of 32 metres using cross laminated timber.

According to Gerard, in order to further foster the usage of timber in the building sector, it is incumbent upon design and construction professionals to improve market awareness by educating clients.

“Perception of fire risk is the biggest inhibitor for timber construction,” said Gerard. “Design professionals need to change perceptions using science – our job is educate people using data and evidence, and alterations to the building code can help reflect this.”

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