Is Eight Stories High Enough for Timber?

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Friday, September 23rd, 2016
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The 2016 edition of the National Construction Code allows for offices, hotels and apartment buildings constructed of wood up to an effective height of 25 metres or eight storeys under a deemed to satisfy (DTS) solution.

For many within the timber industry, this represented a watershed moment which would facilitate greater use of the product within the growing market for medium-rise apartment living.

With the increasing number of mega-tall buildings going up within CBD markets, however, questions surround how much impact this will really have and whether or not concrete and steel will continue to dominate in an environment where buildings are pushing 70 to 80 storeys.

With timber buildings rising to above 20 storeys overseas, meanwhile, further questions surround whether or not eight storeys will be sufficient over the longer term or will instead serve as more of a stepping stone on the way toward taller wooden buildings still.

It should be acknowledged that whilst eight stories is the maximum which can be achieved through a DTS solution, construction of code compliant buildings of greater height than this can be achieved via a performance solution – as was the case with Lend Lease’s Forte apartment building in Melbourne.

Courtesy of the convoluted nature of processes involved, however, the number of projects which go down this path is likely to be limited. Thus for now, mid-rise timber construction in Australia will for the most part be restricted to the eight storeys which can be attained through a DTS solution.

Nevertheless, commentators say the impact of the new provisions should not be understated.

For one thing, the new allowances will open up opportunities for timber within the growing market for medium density apartment dwellings within the middle suburbs of major metropolitan areas, XLam (cross-laminated timber supplier) technical manager Nick Hewson says. Given the expanding nature of the population in major cities and the need to house more people in inner and middle suburbs within closer proximity to transport links and employment opportunities, this is an important area of market growth.

Hewson says the new provision will help to change long-held perceptions under which timber has largely been seen as a low-rise material.

“The way the industry has developed in Australia is the attitude that timber is only for (single storey and low rise) residential construction,” he said. “I think what it (the new provision) does is normalises medium-rise timber in the eyes of the industry.”

In respect of the high-rise market, Hewson acknowledges that limitations due to factors such as strength mean that any idea about 80-storey buildings being made wholly out of wood are unlikely anytime within the foreseeable future.

Nevertheless, he argues that there is still strong potential for timber in tall buildings. Lighter and easier to install than concrete, timber flooring systems offer advantages on major high-rise buildings, he says. Courtesy of those same factors, wood also has potential for use as a material through which to place additional floors on existing buildings – a significant advantage in CBD markets where site constraints restrict the feasibility of demolition as an option and where vertical expansion may thus be the only feasible way through which property investors can derive greater gains from their asset.

Perhaps most exciting from a structural perspective, meanwhile, is the area of timber composite materials. In Vienna, for example, the 24-storey mixed-use HoHo building will have a wooden composite structure supported by a concrete service core to which the timber composite is attached. In a recent experiment in America, meanwhile, a timber concrete composite material was proven to withstand a load eight times that required by code.

Patric Przeradzki, a senior associate at architectural firm Woods Bagot is also optimistic about timber’s future. As awareness about timber’s potential increases, Przeradzki says the pull factor associated with customer demand will strengthen, especially in light of growing awareness about global warming amongst younger generations. If introduced slowly, Przeradzki says developers and the wider construction sector will become more comfortable with using timber within a multi-residential setting over time.

Hewson and Przeradzki’s comments come amid a number of important developments within the timber industry over recent years which have radically altered the potential of the material for use in multi-storey buildings. Engineered timbers such as glulam or cross laminated timber which involve multiple layers of timber being cut and glued together offsite have enabled significant improvements in terms of strength and fire resistance as well as faster and safer construction processes on-site.

The comments also come as the number of tall timber buildings overseas is on the rise. Aside from the Vienna based HoHo building referred, the Brock Commons student accommodation building at the University of British Columbia in the Canadian city of Vancouver which uses cross laminated timber topped out last month at 53 metres, or 18 storeys. In Stockholm, concept designs for the 40-storey Tratoppen (‘the tree top’) using CLT were unveiled in April.

Whilst eight stories does represent a breakthrough, Hewson says this may need to be revisited in a decade or so to see if a more expansive DTS provision might be appropriate in response to improving technology. He says there will be considerable volumes of innovation coming through, whilst a number of projects are already pushing the boundaries of eight storeys under a performance solution.

Przeradzki, meanwhile, says it will be important for the industry to develop a critical mass which is sufficient in order to underpin a viable and sustainable supply chain. Tighter government policy with regard to carbon emissions of construction materials would also help, he said.

Finally, Przeradzki would like to see greater use of timber within public and infrastructure buildings such as airports, train stations and schools – something that would help the public to become more accustomed to use of wood as a high tech structural system.

“That I think would help to shift perceptions,” Przeradzki said.

“Then people will question twice whether or not this (timber) could be used for (multi) residential purposes.”

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