|
|
|
|
Main Menu |
 |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
|
|
|
|
|
|
News |
 |
|
|
|
Timber vs steel. The CO2 debate continued.
Although timber has regularly been touted as more environmentally friendly than steel, it appears from this study that steel can have lower greenhouse gas emissions than timber. This is because earlier analysis has either reduced the system boundary under analysis or reduced the breadth of the environmental parameters. In other words ignored elements that may contribute negatively to the hoped-for outcome?
Energy used for the production of building materials or used to run the buildings themselves, directly or indirectly contributes to air pollution and greenhouse gas emissions. In Australia 30-40% of the nation’s energy use is attributable to building construction and operation.
Carbon dioxide (C02) has been recognised as the most important greenhouse gas attributable to the construction industry.
Using the embodied energy and CO2 analysis of timber and steel, Dr Graham Treloar of Deakin University was able to draw some interesting conclusions. The main difference with these new methods is that a more comprehensive account was taken of factors normally ignored in the timber industry. Factors such as the energy of human labour in harvesting and delivery, how close the mill was to the forest or whether the timber was cured naturally or not, how the waste is treated etc …all of these things impact on the embodied energy figure for timber.
The important thing to consider is that when trees grow they the absorb carbon from the atmosphere at the rate of approximately 250kg carbon per m3 of timber. This carbon remains locked up in the structure of the timber until most of it is released back into the atmosphere when the tree decomposes or is burned, again forming CO2.
When forests are harvested, the underbrush is disturbed, bark and leaves are stripped, and off-cuts and sawdust result. It is common practise to either chip the waste or use it in other products, burn it at site, leave it where it lies, or burn it in the kilns used for drying timber. In this way carbon enters the atmosphere as a greenhouse gas at the rate of about 600kg of Carbon per cubic metre of net timber product achieved.
The mass of CO2 is 3.66 times the mass of carbon.
The bottom line is:
If carbon lock-up is considered in the broader context of forestry practises, then steel is lower in greenhouse gas emissions, especially if re-cycled content is present. (refer graph)
In addition because of the relatively short overall life of buildings, greenhouse gas emissions are increased due to frequent replacement of timber, re-work and refurbishment of building elements.
None of this addresses the issues of other environmental factors, such as local habitat, biological diversity, soil quality and water catchment all of which are to a lessor or greater degree impacted by the felling of forests.
Extracts from paper by Dr Graham Treloar. School of Architecture and Building. Deakin Uni. Geelong.
Summary from our viewpoint:
If timber is such an effective sink for CO2, and CO2 is a major contributor to global warming, then isnt it terribly obvious that we should NOT be knocking down our forests and concealing them within the walls of our buildings when there is a viable alternative construction material available...steel?
Planting extensive new forests is a practical way forward and leaving existing forests in the ground to perform the job they already do well seems to us to be a totally environmentally sensible way forward.
| | 
|
|
|
|
 |
|
|
