17 March 2011 –Favourites: One of the biggest challenges facing designers and construction companies today is the selection of building materials for minimum environmental impact. In his keynote address at Green Cities, Michael Green, principal of Canadian architectural firm mgb Architecture+Design, argued strongly for timber as a superior alternative to concrete and steel, from the suburban home to the tallest high-rise tower.
World housing and climate change are the two great issues of our time and they are interconnected said Mr Green. Given the number of houses that will be needed over the next few decades, if we continue to build the way we are today, particularly in the developing world, an escalation of climate change would be inevitable.
“The reality is three billion people will need an affordable house in the next 20 years. That equates to 40 per cent of the world,” he said. “That means we have to build 100,000 new homes every single day for 20 years, which is obviously something people aren’t getting their heads around in terms of how we’re going to do it.”
The common conversation on the green agenda for housing centres around solutions such as rammed earth, straw, and modular construction, all great ideas but the reality is they are only suburban solutions and modest in scale, he said.
“Today 50 per cent of the world lives in urban environments and we expect that to go to 70 per cent by 2050. So obviously that scale requires another way of thinking about a solution.”
Urban building structures around the world are basically universal and consist of concrete, steel and masonry. Most architects don’t evaluate the choices they make to build with these materials but according to Mr Green it is time they did.
His research has shown that concrete is the largest material on earth by volume used by humans other than water. In terms of carbon emissions concrete is responsible for 5-8 per cent of emissions compared to 1 per cent for airlines and 3 per cent for shipping. Steel represents 4 per cent of world energy.
“To reduce global carbon we have to reduce carbon emissions and remove carbon from the system. The reality is the only thing we build with day in and day out that does that is wood.”
On average 1.6 tonnes of CO2 is stored in a cubic metre of wood and when a tree falls to the forest floor and rots or is burnt it gives off that carbon to the atmosphere, he said. If used for construction it will sequester that carbon for the life of the building and if re-used for further construction there is no more effective material for reducing carbon. “There is no better tool or solution for building carbon neutral buildings,” he said.
Mr Green estimated that the wood used in a typical timber-framed Canadian home stores the equivalent amount of carbon emitted by a family car over seven years.
But for wood to be a viable alternative the world has to become much better at growing timber sustainably. Europe was leading the way in this regard, with a high standard of sustainable forestry methods.
“We must evolve wood structures to compete with concrete and steel. The scale of the problem we face with housing requires innovation in new technology,” Mr Green continued.
Removing the limits on height for timber construction was necessary for it to compete. Building codes around the world currently limit height for timber – in British Columbia the height limit was increased from four to six storeys (15 metres) in 2009, in UK it is 27 metres, whereas in Japan it is 57 metres. A 30-storey hybrid building of timber and concrete is proposed for Austria.
In the past there were no such limits. In Japan, for example, a 19 storey timber temple was constructed in an earthquake zone 1400 years ago and it is still standing.
“We’re now on the cusp of something new with wood but we have to get over the emotional hurdle of building with it. I think in the future we’ll look out on a landscape of wood buildings just like we do with concrete and steel right now and we won’t think twice about it. But for that to happen we need to remove the arbitrary limit to height around the world,” Mr Green said.
The next generation of wood materials include cross laminated timber which involves glueing layers of wood together to form 12 x 2.4 metre panels. While the mass of the panel was similar to concrete, its ability to store carbon and its lower carbon footprint in production made it a vastly better product for addressing climate change.
Laminated strand lumber and laminated veneer lumber are constructed by glueing strands of timber together to form 19.5 x 2.4 metre panels, which are around 75 mm thick and typically used as beams in construction.
Such materials would ultimately gain ground in the construction industry through their cost effectiveness and strength and safety, he said. To help fast-track the process Mr Green’s architectural firm has set up an open source system called, ‘finding the forest through the trees’ to allow the sharing of information on timber technology worldwide.
“It’s about stepping outside the types of conversations we’re currently having and asking what is it going to take to start making the systemic changes that provide us with more choices when we make decisions about what material we build with.”
A mass wood building weighs about half that of a concrete building, a significant advantage in earthquakes as the forces the building is subjected to dramatically reduce with its weight.
But for widescale adoption of wood as a building material developers will need to be convinced that timber buildings will sell and consumers must believe they are not going to burn and that they will stand up to both wind and earthquakes.
To push the wood agenda further mgb Architecture + Design applied for a research and development grant and has discovered through modelling that the strength and resilience of wood has been grossly underestimated.
Using similar construction methods to a traditional concrete and steel building and incorporating a small amount of steel to allow for bend, the firm found that it was possible to build 30 storey timber buildings without any problem.
“We’ve addressed all the technical questions but we are still not able to build them,” Mr Green said.
“We are at a fundamental point in time where we have the choice to go one way or another – we can take traditional knowledge and go much further with it or we can ignore it.”
Green building councils could also push the timber agenda much further by reassessing how they award credits for wood construction.
“Here [in Australia] you only get two points for timber and in Canada it is a struggle to get credits for wood. These systems and building codes need to change – they are not currently keeping up with innovation.”
Note: top photo is from Michael Green’s GC2011 presentation