Why Wood is so GoodPosted: August 20, 2015
Whether it is its natural aesthetic, its remarkable durability, or its carbon sequestering credentials, wood is gaining traction as a building material in lieu of conventional steel or concrete.
Its potential in construction has also prompted the unveiling of regular “woodscraper” proposals across the globe.
Michael Green, a Canadian architect who is globally renowned for championing the tall timber building industry suggests wooden skylines will reach 30 storeys and that we have the technology in place to build themnow.
Nick Hewson, structural engineer at AECOM, agrees but offers a caveat.
“I think timber could definitely have a role to play in 30-storey-plus buildings but they won’t necessarily be entirely timber structures,” he said. “Certain issues can arise when you start to build over 10 storeys that include the lateral stiffness of the building and the shortening of the building over time.
“I think there’s probably a timber building sweet spot between four and 15 storeys for a wholly timber building – the range where it will be most effective.”
So does combining materials defeat the purpose of using timber?
“If you can maximise the amount of timber you are displacing with the amount of concrete you are using, the timber will offset the carbon in the entire building,” Hewson said.
According to Hewson, timber buildings can weigh 50 per cent less than a traditional concrete building. This can extensively reduce the cost, particularly in cases where developers are working with poor ground conditions or where a build site needs extensive outlay onfoundations.
According to Planet Ark’s Make it Wood website, “A comparison with steel and concrete shows that radiata pine structural timber, for example, has a strength for weight ratio 20 percent higher than structural steel and four to five times better than non reinforced concrete in compression.”
The other benefit in the lightness that is wood is around site quality. Particularly in dense cities, where conditions are restrained and space is limited, timber becomes attractive. It is lightweight and easier to handle, according to Hewson.
Topping out with wood is another possibility, as is extra timber levels to existing buildings.
While the world anticipates high wooden buildings, Hewson forecasts that the next five years will be filled with opportunities to apply wood as decking over railway lines. He identifies Melbourne in particular as a city that has many double crossings and an array of potential development sites around its train stations.
“There are such high costs in deck structure so if you can double the yield by placing a building on top, the economics start to make more sense,” Hewson said.
AECOM is also looking into creating “hubs” which could include commercial buildings, green space and social housing in a bid to help deliver affordable homes and amenities in the one area.
In Sydney, Urban Growth NSW has reported an urban renewal for the Central to Eveleigh Corridor which would see over one million square metres of floor space made available along the three-kilometre railway corridor, and Brookfield Multiplex is in the process of planning Federation Square East in Melbourne. All of these provide opportunities for timberconstruction.
Another market opportunity is wooden educational buildings.
While many Australian schools are single storey buildings, as dense conditions continue, they are more likely to become multi-level, vertical schools. Wood can be particularly beneficial for redevelopment projects at schools in which construction is undertaken while the school is operating.
“Timber can help manage a site better,” said Hewson. “Sites are quieter, less dirty, less dusty and significantly safer.
“They’re also quick to construct with a timber building able to be up in a matter of weeks.”
Some studies have found evidence of improved student performance and health in natural environments, yet another argument that wood is good for everyone.
“Massive wood constructions provide a good quality of indoor air and, as a building material, are an ecologically sustainable and energy-efficient choice,” Mikko Jaskari, acting president and CEO of Honka said in 2012.
”We believe that the use of massive logs in day care centres, for example, will increase at the same rate as increasing attention is paid to the well-being of children in present day care facilities.”
While cost is often a determining factor when it comes to building materials, wood is not as expensive as some might think.
“Timber buildings can compete on cost with traditional buildings,” Hewson said. “I think there is an amount of education that needs to happen but we’re in a position where we have a few timber buildings in Australia but until we get more, a lot of clients will still have to face a conservative and perhaps costly market.”
A 2014 study (Cross laminated timber building costs are competitive) by Russell Hixson published in the online Journal of Commerce found that cross laminated timber (CLT) construction is cheaper than conventional methods, though not by much.
When compared to a standard 10-storey concrete building, CLT offered an estimated four per cent cost saving.
Lynn Embury-Williams, executive director of Wood WORKS! BC said that while four per cent is not significantly cheaper, CLT remains competitive.
“The key is having the building expertise. Once contractors really become familiar with this system I think the cost savings will continue,” she said.
Many clients have three fears when it comes to timber buildings:
- Won’t It Burn Down?
- It Won’t Last As Long
- It’s Not As Strong
“It’s more akin in Australia to construct in precast concrete. However, wood can be a robust system – we’re not dealing with small timber,” he said.
Hewson generally refers to the basics of starting a fire – you start with the small sticks to kindle a fire.
“These buildings don’t burn down,” he said.
Last year in a video series with the Washington Forest Protection Agency, Green described timber buildings as “incredibly safe” when it came to fire.
“Fire incidents in heavy timber buildings tend to result in smaller fires, as large timber sections have an inherent fire resistance,” he said. “Additionally, charring in the heavy timber member will delay the onset of combust providing greater time for fire fighter intervention.”
When it comes to concerns of durability, Hewson cites the leaky buildings arising across the Tasman partly due to poor workmanship and design.
“If you look to Europe who have big timber buildings that have stood for hundreds of years – they don’t have this this problem,” he said. “There is no reason timber buildings shouldn’t last as long as masonry and concrete. It’s very much about the individual site.”
Contrary to what some may think, there is very little maintenance on a timber building assuming it has a weatherproof skin. Hewson has a couple of suggestions when it comes to maintenance.
First, he suggests selecting a timber species that’s durable. Hardwoods last a long time – you just have to accept that it will weather and change appearance over the years.
Less durable species can be treated with paints, oils of other finishes, though this will require more prepping and coating over the long term.
So will the skylines of the future indeed be made of wood?
“There will always be naysayers, just like the Eiffel Tower that people said couldn’t’ be done,” Hewson said. “I certainly think in our lifetime there will be timber buildings over 30 storeys. The engineered timber industry is still in its infancy. There are products and ideas we haven’t even thought of yet.
“As of buildings 10 to 15 stories, this can happen now. But let’s not overlook other opportunities including lower multi-residential, rail decking, schools and topping off of towers.”
Looks like there is plenty to keep the Australian timber market hustling.