Environmental and energy balances of wood products and substitutes

Life Cycle Assessment

In recent years there have been increasing discussions and investigations on environmental impacts resulting from growing consumption of energy and raw materials on one side and emission of solid, liquid and atmospheric waste on the other side. Since the early 1980s, issues such as global warming, ozone degradation in the stratosphere, depletion of natural resources, acidification of water and soil, human and eco-toxicity, etc., have engaged scientists and environmentalists all over the world to develop new methods towards environmental impact assessment. One of the methods being developed for this purpose is the LCA of products.

During the last decade, environmental aspects have become more important and the impacts on nature, consumption of non-renewable materials and energy, and sustainability are important issues concerning design and manufacture of products and their end of life, i.e. recycling, burning or landfill.

The new approach to environmental conservation is a more comprehensive one. Sustainable management of natural resources includes both the minimal consumption of materials (renewable or non-renewable) and the protection/conservation of the environment. Technical measures serving to achieve the goal of sustainability are: energy saving, improved use of materials, reuse and recycling, emission control, etc. Some of these measures can also have a positive economic effect such as the case of waste paper recycling.

Wood, as a renewable raw material, has been used worldwide for a broad range of end products as well as for renewable energy generation. There are sectors where wood is facing substitution pressure from other materials such as synthetics, concrete, ceramics and glass. This pressure could be reduced if the sustainability of forests and roundwood production were guaranteed, and if consumer awareness of the ecological benefits of wood-based products were enhanced.

The selection of a material for specific end uses strongly depends on its physical and technological suitability, but the cost aspect is also of extreme importance. Due to increased awareness of environmental aspects, certain issues such as low energy demand for producing wood products, possibility of recycling and utilization of waste wood for energy generation at the end of life cycle should be taken into account so to demonstrate the advantage of wood when comparing it with other materials.

LCA is a useful tool for comparing the environmental aspects of specific products as it enables the ecological comparison of two or more products made of different raw materials but used for the same purposes. The results of a comparative LCA study provides useful data for decision-making when selecting environmentally sound fuels, raw materials, products and production processes.

LCA is an approach to study the environmental aspects and potential impacts throughout a product’s life from raw material acquisition or production (e.g. wood production in the forest) to manufacturing, use, recycling and disposal.

The ISO/EN 14040 defines LCA as a technique for assessing the environmental aspects and potential impacts associated with a product by:

  • compiling an inventory of relevant inputs and outputs of a system;
  • evaluating potential environmental impacts associated with those inputs and outputs; and
  • interpreting the results of the inventory analysis and impact assessment in relation to the objectives of the study.

As a useful tool of decision-making, results of LCA are applied by different groups such as producers’ associations, environmental organizations, policy-makers and consumers. The critical consumers are particularly interested in information on the ecological relevance of the commodities and products of short-term and long-term use. For the producer, marketing aspects and ecologically-based optimization of production and processing can be of the highest priority so the critical consumers are satisfied and energy and material costs are reduced.

LCA also gives the possibility to environmental organizations to increase public awareness on environmental aspects and consequently urge policy-makers to provide frameworks for adequate laws and regulations.

Figure 1 shows the four steps prescribed by ISO/EN/DIN 14040 (Scharai-Rad et al., 1997).

Figure 1: Four steps of a life cycle assessment


Goal and scope definition

The goal shall state the intended application, the reasons for carrying out the study and the intended audience. The scope describes among others the function, functional unit, product system to be studied, product system boundaries, allocation procedures, types of impacts and methodology of impact assessment, data and data quality requirements, assumptions and limitations.

The primary purpose of a functional unit is to provide a reference to which the inputs and outputs are related. This reference is necessary to ensure comparability of LCA results. Therefore, the functional unit shall be clearly defined and measurable. For wood products, 1 m³, 1 tonne or 1 m² are usually taken as functional units. Moreover, the moisture content of the product to be studied shall also be specified. For a precise functional unit, oven-dry condition is recommended.

The system boundaries determine unit-processes or life cycle phases to be considered within the framework of an LCA study. The criteria used in establishing the system shall be identified and justified in the scope phase of the study.

The data quality requirement should address time-related coverage, geographical and technology coverage, precision, completeness and representativeness of the data, consistency and reproducibility of the methods used, sources of the data and uncertainty of the information.

Life cycle inventory analysis

The life cycle inventory (LCI) indicates the relevant inputs and outputs of a product system. It includes on the input side energy (electric and thermal) and materials (raw materials, semi-fabricated products, supporting and operating materials) and on the output side products, by-products and releases to air, water and land. Generally, processing machines, buildings, manpower and the use of land necessary for transportation or biological production are not included in LCI otherwise the inventory analysis would become very complex.


A complete LCI comprises all phases of a product life cycle. In the case that the system boundaries defined include only one or few life cycle phases (e.g. production and use of certain products), the collected data must cover the phases concerned (Figure 2).

Figure 2: Life cycle phases to be considered within the framework of LCA studies

When dealing with systems involving multiple products, allocation procedures are needed (e.g. multiple products from petroleum refining). In the timber industry there are often products and by-products where products are, for example, sawnwood or furniture and typical by-products are different types of residues which serve as raw material for other products such as particle board, fibreboard or pulp and paper.

Electric and thermal energy, together with renewable and fossil energy, and the relevant energy mix and efficiency, should be taken into account when calculating energy consumption and the resulting emissions.

Figure 3 shows the life cycle of a timber-based roof. It comprises the phases “roundwood production in the forest”, “sawnwood production in the sawmill”, “production of roof elements in the carpentry and roof assembly at the construction site”, lifetime (using time) including demolition and waste wood utilization (recycling and burning). It is also necessary to consider the transportation between the life cycle phases. The transportation can be analysed either separately for each phase or for the entire life cycle.

Figure 3: Life cycle of a timber-based roof


A complete LCI includes the energy and material flow for all phases. In this case, the system boundaries are the beginning of roundwood production and the end of life cycle (recycling or burning of waste wood). LCA studies are often confined to a few life cycle phases, but it is possible to reconstruct the entire life cycle by using two or more studies as literature sources.

For the roof as a timber-based product, the flow of material and energy is illustrated in Figure 4. The output of one phase (e.g. wood production in forest) is the input for the next phase (e.g. sawnwood production). However, there are some output materials (e.g. thinnings, emissions resulting from fossil fuel) that leave the boundary system. Thinnings as forest output leave the forest along with roundwood. While roundwood remains within the boundary system, thinnings leave the system and are utilized as fuel or as raw material for paper and oriented strand board (OSB) production. Emissions such as CO2 or NOX are released to the atmosphere and, therefore, they also leave the boundary system.

Figure 4: Life cycle assessment of a roof construction  (see definition of life cycle inventory)


Beside roundwood and energy there are also other inputs and outputs such as operating materials, supporting materials, residues, different types of emissions, etc., that partly remain in the system and partly leave the boundaries. Showing all these materials in one figure leads to confusion, therefore, Figure 4 is not complete and shows only the main stream.

Life cycle impact assessment

The life cycle impact assessment is aimed at evaluating the significance of potential environmental impacts using the results of LCI. The level of detail, choice of impacts evaluated and methodologies used depend on the goal and scope of the study concerned. For a proper impact assessment the following three steps are generally necessary:

  • Classification: assigning of inventory data to impact categories;
  • Characterization: modelling of inventory data within impact categories; and
  • Valuation: possibly aggregating the results in very specific cases and only when meaningful.

The impact categories can be based on global, regional, local and other criteria and these are described below.

Global impact categories

Regional impact categories

Local impact categories

Other impact categories

  • use of resources (renewable and non-renewable), water and land
  • greenhouse effect/GWP
  • ozone degradation in the stratosphere
  • release of persistent toxic substances
  • acidification of water and soil
  • waste disposal/landfill
  • human toxicity
  • eco-toxicity
  • photochemical ozone creation
  • use of land (transportation roads, need of large areas for biological production)
  • noise
  • unpleasant smell, etc.

Life cycle interpretation

According to ISO/EN 14040, interpretation is the phase of LCA in which the findings from the inventory analysis and the impact assessment are combined together. The findings can result in conclusions and recommendations to decision-makers, consistent with the goal and scope of the study. Moreover, the findings should reflect the results of any sensitivity analysis that is performed.

Concerning other aspects, such as comparisons between systems, critical review and reporting, the authors refer to:

_ ISO/EN 14040: Environmental Management – Life cycle assessment – Principles and framework

_ ISO/EN 14041: Environmental Management – Life cycle assessment – Life cycle inventory analysis

_ ISO/EN 14042: Environmental Management – Life cycle assessment – Life cycle impact assessment

_ ISO/EN 14043: Environmental Management – Life cycle assessment – Life cycle interpretation

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