“Wood is the only building material that helps tackle climate change.”
So reads a statement on the web site of the Planet Ark Environmental Foundation, an Australian not-for-profit organisation which promotes living in harmony with nature.
Planet Ark is not alone in promoting wood. As timber becomes more common in multi-story buildings, belief is growing the material can benefit both the environment and occupant wellbeing.
Ralph Belperio, Major Projects & Timber Expertise Leader at engineering consultancy Aurecon – the design firm behind Australia’s tallest engineered timber office building at 25 King Street in Brisbane – describes responsibly sourced timber as ‘the only truly renewable building material available’. Whilst stressing that those at his firm are not ‘timber zealots’ and would consider hybrid solutions where properties of concrete or steel are more suited to overcome specific design challenges, Belperio says Aurecon seeks to maximise timber use where possible as part of its responsibility to the environment.
Not surprisingly, other industries dispute timber’s environmental benefits relative to those of their own product.
In the concrete industry, for example, Ken Slattery, Chief Executive Officer of concrete industry lobby group Cement Concrete & Aggregates Australia, says that ‘few products, if any, can claim to provide the environmental, social and economic benefits that concrete can offer’, and that ‘it’s hard to imagine a product with better sustainability credentials than concrete’. (Others dispute this, pointing to the volume of greenhouse gas emissions in cement manufacturing processes.)
Furthermore, even timber enthusiasts acknowledge that the material’s sustainability credentials depend on it responsibly sourced. Adam Jones, structural engineer at WoodSolutions and recognised by the Green Building Council of Australia as Future Green Leader of the Year in 2019, describes timber buildings ‘conditionally beneficial’ for the environment.
Nevertheless, wood’s growing popularity raises questions about its role in promoting sustainability.
For answers, Sourceable contacted Belperio as well as Duncan Mayes, EGM – Innovation & Emerging Business at Timberlink Australia. Both are set to deliver keynote presentations at Frame Australia’s Timber Offsite Construction conference in Melbourne on June 17th. Both provided written responses to questions.
According to Planet Ark, responsibly sourced wood has several environmental benefits.
First, there is timber’s ability to sequester and store carbon. As trees grow, they absorb carbon dioxide and store carbon. When responsibly harvested and made into wood products, the carbon remains stored in the wood over the life of the product and is locked away rather than being in the atmosphere. Thus where a tree is grown for 30 years before its wood is harvested for use in a building which lasts fifty years, the carbon absorbed by that tree is locked away for eighty years.
This is significant. According to Planet Ark, around half of the dry weight of wood is actually stored carbon.
Next, the production and processing of wood is less energy and carbon intensive compared with that for most other materials. As a rule of thumb, Planet Ark says, conversion of once cubic meter of solid materials such as concrete or brick for one cubic meter of timber will avoid the emission of approximately one tonne of carbon dioxide into the atmosphere.
Third, wood is a good thermal insulator due to the air pockets within its cellular structure. Wood, Planet Ark says, is 15 times better as an insulator compared with masonry or concrete, 400 times better than steel and 1,770 times better than aluminium. This helps reduce energy consumption and cost in heating and cooling.
Belperio says wood offers several benefits – environmental and otherwise.
First, timber naturally lends itself to a large amount of prefabrication. Whilst this necessities more design work up front, it delivers benefits on site in terms of a lesser requirement for workers; less scaffolding; elimination of the need back-propping; fewer crane and truck movements; overall reductions in cost, noise and time; and safer work sites.
On sustainability, Belperio says the timber design at 25 King Street achieved a 74 percent saving in embodied carbon against comparable concrete and steel buildings. As well, the ‘warmth’ from the exposed timber structure in the interior delivers social benefits as research has shown that use of natural materials better connects occupants with nature and create a happier and healthier environment.
To be sure, Belperio acknowledges that other materials such as concrete, bricks and steel have advantages over timber when it comes to fire rating requirements, durability, susceptibility to termites and moisture ingress. As well, timber’s lighter weight can create issues with acoustics and vibration.
Nevertheless, he says these issues can be mitigated through effective design.
Mayes broadly agrees.
He says the cellular nature of wood which has a lower density compared with materials such as concrete and steel means that it has a lower thermal conductivity compared with these materials. This means that both heat and cold transfer less easily with wood compared to with metal.
Take, for example, the comparison of timber with metal frames and doors. In summer, Mayes says metal door and wall frames can conduct temperatures which are well over 50 degrees Celsius in direct sunlight, causing excessive and unwanted heat transfer into buildings. In winter, metal frames create a cold bridge which sees cold air transfer through the frames even where argon-filled double glazing is used.
By contrast, use of wood frames delivers greater insulation and thus helps to reduce heating and cooling costs.
As for other materials such as concrete or natural stone, Mayes says these can be used in combination with timber to store and prevent heat transfer into buildings. Roof eaves can also reduce the volume of sunlight which enters into buildings during the hottest times of day.
As well, Mayes says wood is good for health and wellbeing. As a ‘breathable’ material, wood has a greater ability compared with gypsum or cement to store excess humidity during peak times and to release this as humidity outside decreases. Therefore, use of timber in building interiors can help to facilitate a balancing act and to maintain humidity levels within the 30 and 50 percent ranges which are considered optimal both for comfort and for avoiding infections, skin irritations, bacteria and other ailments.
Asked about the merits of timber across building types such as detached homes, multi-storey residential, offices, hospital or schools, Belperio stresses that timber’s benefits are no more pronounced in any particular building typology over and above any other. He says the are solutions to each building type which are specific to timber and that any challenges can be addressed through effective design. Where other materials such as concrete or steel are more suited to challenges at hand, a hybrid solution involving those materials in combination with timber will often be considered.
As for considerations of traditional timber framing against engineered timer, Belperio says traditional framing systems (studs, joists, beams, rafters) are ideal for lower rise buildings due to the ease and speed of their construction. Engineered timber, however, is better where large spans or improved fire performance are required, particularly when the timber is to be exposed. Unless the timber can be clad in fire-resistant material such as suitable plasterboard, Belperio says unprotected timber framing is not ideal where fire ratings are required.
When using timber to improve sustainability, Belperio and Mayes say several issues should be considered.
When designing with timber, Belperio architects and engineers should think about shrinkage, deflection driven design and connection options. Consideration must also be afforded as to how timber’s structural limitations will be managed. These include shorter structural spans which increase the number of columns and reduce the wide spans often expected in commercial floorplates. Finally, to enable prefabrication, thought must be given to project delivery. This includes resolving the design, coordinating procurement and services and finalising details ahead of construction. This is important as making on-site adjustments is difficult in a prefabrication environment.
Mayes says architects should take greater account of annual macro and meso climatic conditions to which buildings are exposed and should utilise the functionality of materials in a smarter way. Solar shading, use of high insulating materials such as wood, and applying thermal mass to surfaces to prevent heat transfer should all be considered. Greater use should also be made of natural ventilation and dynamic airflow. Smart use of wood and natural breathable materials will help to create a more stable and balanced interior environment and a calmer atmosphere, he says. Acoustic properties of wood on interior surfaces should be maximised to prevent unwanted echoes, reverberation and medium to high frequency sound transmission – an area in which hard and dense materials such as glass, ceramics and metals are not as effective.
Australia faces challenges in addressing climate change and reducing building energy costs.
If sourced responsibly, timber has a role to play.