From seedling to sawmill – a life cycle analysis of framing timber
This is a part of the
Life cycle costs
feature
The Forest Research Institute was recently commissioned by BRANZ to carry out an extensive life cycle analysis study of timber to assess its environmental impact from the planting of the tree until it leaves the sawmill.
One of BRANZ’ main roles is providing scientifically sound information to the building industry. Until recently, the scope of this information typically dealt with a material’s durability, and the fire, structural and thermal aspects of buildings. Now, designers and specifiers are becoming interested in the environmental aspects of materials. The questions which are increasingly being asked are:
• How do the environmental impacts associated with using different materials vary?
• Can we improve the overall environmental performance of our buildings?
These are often not easy questions to answer.
There are various ways to assess the environmental burden of building materials. The more comprehensive assessments consider the environmental implications during the whole life cycle of the material, from resource recovery to disposal after use. The most rigorous of these approaches applies the procedure of life cycle analysis (LCA). LCA provides a comprehensive, objective framework to assess products throughout their entire lives. The LCA framework comprises of four stages, and is outlined in the article entitled “Life Cycle Analysis” on Page 38. Procedures for LCA are becoming recognised internationally, with numerous organisations having input into standardisation of protocols.
New Zealand LCA studies
Currently, there are few studies in New Zealand based on life cycle analysis — the most widely available are the New Zealand Institute of Architect’s publication Building Material Environmental Data Sheets. These data sheets are qualitatively based, and cover most of the major building materials. Although these data sheets are an important first step in providing qualitative information to the New Zealand building industry, the need for current quantitative information is also being recognised. To fill this gap, BRANZ has started making quantitative assessments of the major building materials.
Sawn framing timber study
Recently, an LCA study of sawn framing timber was undertaken by the Forest Research Institute on behalf of BRANZ. The inventory analysis assessed the material and energy flows associated with the production of this product up to the mill gate. Thus, the forest’s establishment, silviculture, harvesting, transporting and wood processing stages were all considered. What happened to the sawn timber after final processing was outside of the scope of this assessment. It is intended that future studies will consider this.
The timber study investigated the following material flows for preparing seedling trees; previous land use on which forests grow; varying site preparation methods; the effect of haul distance for logs; varying silviculture regimes, and different harvesting systems. The study also examined the production of three common type of framing-grade sawn timber which had the following treatments:
• boron treated, air dried
• untreated, kiln dried
• treated, kiln dried
For each of the three types, the inputs and outputs associated with their production were considered in detail. Thus the energy and water inputs, green house gas emissions, and particulate and volatile organic compounds emissions were assessed. All input and output figures were based on a set quantity of material ̶ 1 odt (oven-dried tonne) of framing timber.
In conducting LCAs, there are often many assumptions made, because of the complexity of the task. For this study, the following assumptions were made:
• the sawn timber was derived from a typical North Island Pinus radiata plantation
• the effect of recycling or reusing chips produced at the sawmill for other wood processing plants was ignored
• a standard sized mill was used to process the timber
Study findings
Based on what was defined as the base case condition (that is, the system used to produce kiln-dried framing most commonly used in New Zealand today), the study found that energy and water were the major resource inputs used to produce framing timber.
The energy inputs were sourced from the consumption of a number of different fuel types, including diesel, petrol, electricity, natural gas (where timber is dried in gas-fired kilns) and biomass. Water is used for forest establishment (in nursery operations) and for water cooling of saws during processing. Other inputs, such as forestry chemicals and fertilisers, are low. Chemicals account for less than 10 grams per odt of framing timber, and fertilisers account for 400 grams per odt of framing timber.
Wide range of applications
The information from this type of study can be used in a wide range of applications, and is not limited to environmental issues. For example, it can address and refine day-to-day operations, and can also tackle long-term management planning issues. Some specific applications of LCA studies include:
• process rationalisation
• energy audits
• material waste audits
• ISO 14 000 (environmental management standards) compliance
• future carbon taxes/tradeable emissions.
For more
BRANZ, with FRST and Building Research Levy support, is carrying out similar studies on other construction materials. For more information on this research project, please contact Roman Jaques at BRANZ on tel (04) 238 1342 or e-mail: [email protected]
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Articles are correct at the time of publication but may have since become outdated.
