Will Wooden Skyscrapers Stand the Life Cycle Test? 1

Wednesday, April 22nd, 2015
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Architect Michael Green predicts that the future will see wooden skylines, with structures reaching as high as 30 storeys.

Green also believes the greatest barrier to wooden building is education as opposed to engineering – he himself works from a 105-year-old, seven-storey wooden building office in British Columbia, Canada.

Melbourne based Jack Haber, managing director of Tecbuild Systems, feels the new wave of skyscrapers will see architects exploring different materials – wood being one of them.

He believes there is room for tall wooden buildings in cities and shorter buildings in suburban areas, though he feels there is room for a variety of materials.

“For me, given the sophistication but also complexity of the contemporary construction industry, hybrid structures that seek to exploit the best properties of different materials in appropriate applications are the way forward,” Haber said.

Haber added that while steel and concrete have long been staples in creating today’s skylines, the materials are doing more harm than good.

“There is no doubting the proven capabilities of steel and concrete in structural systems, particularly since the Modernist era,” he noted. “They are just not the total answer.”

“Concrete production represents roughly five per cent of world carbon dioxide emissions. The production and transportation of concrete represents more than five times the carbon footprint of the world airline industry as a whole.”

In a Ted Talk last year, Green said a typical 20-storey concrete building emits 1,215 tonnes of carbon dioxide, while wood sequesters 3,150 tonnes of the gas for a net difference of 4,356 tonnes – the equivalent of removing approximately 900 cars of the road each year.

While wooden skyscrapers seem to tick all the boxes when it comes to environmental performance, skepticism surrounding their longevity abounds. Some architects will point to the world’s oldest steel frame skyscraper – New York’s 57-storey Woolworth Building built in 1913 still-standing stone and brick buildings in Rome.

Haber, however, is quick to note the oldest multi-storey wooden structure that remains standing – the  nine-storey, 67-metre Yingxian Pagoda in northern China.

Constructed in 1056, the building sits on a stone foundation but the structure is made entirely of wood.

“The pagoda has survived over 900 years of seismic activity, including more than seven strong earthquakes, with minimal damage,” Haber said.

He also cited the recently announced HoHo project by Austrian real estate firm Kerbler Holding GmBH, an 84-metre wooden-hybrid mixed-use residential and commercial skyscraper in Vienna.

“The HoHo project proposes wood composite floors, secured to the central concrete supporting cores, and that extend out to the building edge,” Haber said.

“These floor panels are supported by a wooden column system around the outline of the building. This structure then supports pre-fabricated external wall modules that combine solid wood panels with a concrete shell elements to form the building’s facade.”

Haber offered insight into exactly what is structurally sound when it comes to a wooden building, starting with the two types of contemporary engineered timber: massive and framed timber.

“Massive timber, as the name suggests is a wonderful way to increase sequestered carbon,” he said.

However, in Australia, this material is not a priority with the country questioning its viability versus its cost, particularly with some utilitarian structures.

“Timber is a commodity that is sold by the cubic meter – the more you use, the higher the materials cost,” Haber said. “This is particularly so with factory-produced precision timber panels. In many applications, only a frame is necessary.”

Framed timber structures are more common in Australia, and they offer a little more design flexibility.

“A key concept in structural engineering is elegant design – a slender, elegant structure uses only material structurally required to carry the load or force in question,” Haber said.

“We have developed framed load bearing structures to be highly efficient and cost effective. Framed timber buildings use relatively inexpensive insulation and board products to infill the gaps and clad or floor a framed timber skeleton.

“Wall frames and floor cassettes can be built offsite for speed of erection and engineered joists can span further, carry greater dead loads than massive cross laminated timber (CLT) as well as taking point loads.”

He noted that where shear walls are called for, panels are relatively light but offer excellent buildability and load-bearing capacity

As façade elements, Haber said the precision fabrication of CLT can lead to considerable time savings during erection and subsequent fitting of window elements.

Finally, a paper that studied the life cycle assessment of four detached single-family dwellings in context for their wood usage found that wood appears in almost all stages of buildings’ life cycles.

The study took into account the full life cycle of the buildings, including the production of building materials, prefabrication, transport to the building site, building, use, demolition, transport of waste and final disposal of waste.

It found that “wood and wood-based materials, are the only ones from among the analysed building materials, that have shown an environmental benefit both from the ‘cradle-to-gate’ (stage 1) and ‘gate-to-grave/reincarnation’ (stage 7) perspective.”

“Nevertheless, any timber building, whether framed or massive, will be far superior as a sustainable low carbon structure than a comparable structure built in concrete or steel,” Haber said. “If we are serious about lowering our carbon footprint then hybrid timber systems are a logical and necessary innovation.”

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  1. Daryl

    a good article but I would have to challenge some of the "facts" such as flexibility of massive timber versus frame and dead load capacity of massive versus frame. Frame has been seen to be very effective in small buildings for several centuries but when we start talking about projects of scale (more than 6 levels) then massive timber has significant advantages over frame as evidenced by a range of projects appearing around the world and reported on this site in recent months.