Wooden Buildings: Your Questions Answered 3

Thursday, July 23rd, 2015
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“Wooden buildings are the future – without doubt,” Andrew Waugh, founder of Waugh Thistleton Architects.

This may seem like a bold statement, but he certainly doesn’t stand alone in that belief.

It’s been a big year for wooden buildings and there is growing global support for their prioritisation as a building material, particularly for multi-storey projects.

The Council on Tall Buildings and Urban Habitat has dubbed 2015 the year of the “Woodscraper” while the United States Department of Architecture (USDA) is currently reviewing entries for the recently launched US Tall Wood Building Competition, for which Waugh is a judge. A US$2 million prize is at stake while globally, the wooden project pipeline is full of activity.

Waugh’s firm is behind Dalston Lane, the record breaking cross laminated timber (CLT) residential block that will become the tallest in the UK at 10 storeys.

The 121-unit development is expected to use more timber than any other project in the world, making it, by volume, the largest CLT project globally.

Austrian real estate firm Kerbler Holding GmBH recently unveiled plans to build HoHo, an 84-metre wooden-hybrid mixed-use residential and commercial skyscraper in Vienna while the 14-storey wooden Treet building in Norway is also under construction.

Over in British Columbia, Canadian architect and wooden building advocate Michael Green has proposed an urban project for the Réinventer Paris competition called Baobab. It is set to feature the world’s tallest wood building at 35 storeys and would see Paris define the next era of city building according to Green’s firm.

In Melbourne, Forté, a 10-storey wooden residential building in the Docklands is still earning praise for its groundbreaking construction efforts years after it was completed in 2012.

Despite these success stories, the majority of buildings being constructed today are still using concrete and composite materials reflecting the resistance from the industry to use wood.

Now a lot has been said on wood, but there are also plenty of questions surrounding its use in tall buildings. Some common questions are:

  1. How tall can we see wooden buildings rise?
  2. Will they burn to the ground if a fire ignites?
  3. Will termites eat them up?
  4. What are the consequences if we don’t build with wood?

High Hopes

The big question every one wants to know is: how high can we go?

Green has suggested that wooden buildings could rise up to 30 storeys, but his recent proposal for the Paris building tops those ambitions at 35 stories.

Waugh, however, thinks we’re asking the wrong question and should just focus on building with wood – at all heights.

“It is a glamorous question and good for press and lovely pictures – but I doubt this is the way to build sustainable buildings that will solve the global housing crisis,” he said.

He also believes height will not necessarily give greater density.

“The competition over height – actual buildings and hypothetical ones – is interesting and pushes the boundaries of our understanding, but this conversation is in danger of being sensationalist,” he noted. “We need to make timber buildings the norm not the exception.”

All Fired Up

Wooden building critics are concerned that wooden buildings will be susceptible to fire.

Green has identified tall wooden buildings as “incredibly safe,” while Waugh points out that fire is a serious issue for all means of construction.

“Engineered timber is predictable under fire, it burns at 0.7 millimetres a minute and it self protects through forming a charring layer on the surface as it burns,” he said. “Fire engineers and fire officers alike are in favour of solid timber – not timber frame – construction.”

Nick Hewson, senior structural engineer at Aecom also touted the safety of timber construction.

“Timber does have some inherent fire resistance as it chars and insulates the wood below,” he said. “The timber we’re likely to use for these buildings is going to be very large by comparison with normal domestic timbers and takes a very long time to char and offers excellent inherent fire resistance.”

“The effect can be observed in areas after bush fires – trees with large diameter trunks are still standing with their heartwood intact while the smaller trees have all burnt down.”

Termite Trouble

If fire isn’t as much of a concern as many believe, what about the wood eaters – the termites?

According to Jack Haber, managing director of Tecbuild Systems, it’s all about the pre-treatment of wood.

“Where subfloors are specified with structural joist of floor cassette systems fabricated using Tecbeam joists, H2S termite treated LVL is used to protect against termite attack,” he said.

The Australian Timber Database (ATD) lists several types of treatments available across different hazard levels.

“Some treatments protect the timber against borers and/or termites; others protect the timber against insects, borers and decay,” the ATD website states.

One treatment, for example, is Creosote and Pigment Emulsified Creosote (PEC) which houses heavy-duty preservatives used to protect such commodities as poles, sleepers, marine piles and engineering timbers against decay and insects, including termites and marine borer attack. According to the database, these oil-borne preservatives also provide excellent weather protection, are long lasting and do not require maintenance treatments.

Hewson also believes there can be work done in the foundation to prevent termites.

“Typically the timber is well protected and separated from direct contact with the ground, often by a concrete slab or podium structure with physical protection measures mandated by Australian Standards,” he said.

Concrete Consequences

Strine Environments in Australia note that concrete is the most widely used building material in the world, with approximately two tonnes of concrete use for each person on the planet earth.

Waugh stands behind that research and says there would be “terrible implications” for the environment if we continue building with concrete and other environmentally damaging materials.

“The production of cement is the crime against the environment that no one is talking about,” he said. “We have to adjust the whole construction industry to using as little cement as possible – we need alternatives, of which timber is only one…the best one so far.”

While concrete is usually seen as the primary carbon-causing culprit, other materials are also high in terms of emissions according to Narangba Timbers in Queensland:

  • A cubic metre of steel releases 5,320 kilograms of carbon into the environment
  • A cubic metre of concrete releases 120 kilograms of carbon into the environment
  • A cubic metre of aluminium releases a shocking 22,000 kilograms of carbon into the environment

The Journal of Sustainable Forestry reports that by using wood substitutes, we could save 14 to 31 per cent of global CO2 emissions and 12 to 19 per cent of global fossil fuel consumption by using 34 to 100 per cent of the world’s sustainable wood growth.

The Dalston Lane project’s CLT construction will offer immense benefits over an equivalent concrete frame. Taking into account that timber stores carbon by absorbing CO2 from the atmosphere, known as sequestered carbon, the structure will be considered carbon negative.

“(The project) will use over 3,800 cubic metres of timber and around 1 million fixings, but this represents just a fraction of the materials that would have been used if Dalston Lane was built with traditional materials,” said Gavin White of Ramboll, the project’s CLT engineer.

Similarly, the Treet building in Norway is expected is expected to sequester approximately 1,000 metric tons of CO2.

So, where to now for wood?

“We are at the beginning of a wooden revolution – these buildings store carbon, they’re fast accurate and safe to build – and they are great places to live in,” Waugh said.

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  1. Nick Hewson

    It's all go in London with big CLT projects at the moment. With Dalston Lane, the 10-storey CLT-steel hybrid building at Wenlock Road and a few more Lend Lease apartment buildings there it's showing the rest of the world how it's done.

    We're looking forward to getting some more CLT buildings up in Australia in the near future!

  2. Catherine

    This is all folly and generated by contractors wanting to build fast and cheap.
    There will be major fire disasters when the sprinklers don't work or some such obvious eventuality.

    • Steve

      Steel and concrete buildings also fail when sprinkler systems fail. They are not impervious to fire.

      This is not greed-driven folly, but simply a thoughtful and creative use of resources.