As an ecological and multi-purpose material, wood has to better valorize its various assets to maintain and enhance its market share in the current context of hard competition between materials.
To do so the South West European forest-wood chain seized the opportunity of the transnational project DEFOR « Développement Forestier » to build a tool to support communication on wood. In this framework the European Institute of Cultivated Forest inventoried the major technical and scientific documents describing woods advantages and limits in comparison with main competitive materials. These references which concern various uses (building, framing, furnishing, energy, etc.) should provide the forest wood chain with documented arguments on wood assets to improve and facilitate its promotion. These documents have been available on line since October 2008.
The main conclusions converge toward the same idea: if wood is not the only solution, its multiple advantages, including the fact it is infinitely renewable, make it a major material for the future for many everyday and industrial uses.
METHOD
This comparative study done in 2008 aims to provide objective and argumented elements on wood compared to other materials. The search was limited to references coming from reliable sources and with no financial links to the material chains. It mainly acts of studies done :
— for or by international organisations (European commission, Food and Agricultural Organization, World Health Organisation, international agencies, European Forest Institute, etc.),
— national public organisms (ministries and other institutions, environment or health national agencies, etc.),
— Research or technical institutes (INRA, Forest Research, universities, several research consortium, etc.),
The documents, often in English or in French, come mainly from prospecting on websites of the organisations above and from requests on scientific search engines (documentary resources INRA, ISI Web of Knowledge…). When available studies comparing wood and other materials were favoured. In the other case, studies on wood properties were retained according to their level of precision and coherence with the focused themes. In case of contradictory results the proportion of different opinions was preserved. It is however important to notice that this bibliographic study is not exhaustive. The references were compiled in an on-line database and identified by a number of key words corresponding to:
— a material (or several in case of comparative studies or general documents),
— a product use (building, packaging, etc.),
— one or several themes (mechanical properties, ecological impact, etc.)
A search by key words or thanks to pre-set questions gives a list of bibliographic references, related general information and abstract. A link toward full text is generally available but depends on the user access authorization to linked websites. Thus more than 280 references are at the disposal of general public on www.iefc.net website. It is also possible to help improve this database by directly proposing documents to IEFC.
MAIN RESULTS
The synthesis of the referenced documents presents for wood undeniable environmental qualities, various technical assets and limits in comparison to main competitive materials and refutes some preconceived ideas
1. Major asset : an ecological and renewable material
With growing preoccupations on climate change and new energy sources in the last years, forest and wood have been in the focus of numerous studies on carbon stock potential, ecological print or conditions of wood resource sustainability. It often acts of studying substitution opportunities of products or materials by wood or wood products. Thanks to its renewable nature, its low cost and abundant presence in many places in the world, wood indeed appears to be a candidate more than interesting for the conception of a sustainable future.
Moreover, forest is expending in Europe. It covers 193 million hectares and unlike world’s tendency to deforestation, increases of around 756 000 hectares each year according to FAO. It is thus underexploited and landscape are closing more and more with forest spread. This under-exploitation becomes a threat for the forest itself which needs to be valorized (that is to say more mobilized) to assure its own maintenance and renewal. Its resource durability depends on the forest management practices implemented. In Europe, policies and tendency head toward sustainable forest management, as illustrated by the continual increase of certified forest areas.
The carbon stock nature of wood is another important ecological asset in favour of this material. An exploited forest contributes to decrease the greenhouse gases amount in the atmosphere by storing the air carbon dioxide. This environmental advantage could constitute in the future a political argument toward a larger use of wood compared to fossil materials, leading to forest renewal. The referenced documents present conversion factors between matter and carbon and scientific values about wood carbon storage capacities.
A large number of studies also evaluates with precision the ecological and energetic impacts of materials using Life Cycle Assessment (LCA) method. This analysis allows to perform accurate comparative studies between materials for one given use. Numerous existing studies focus on ecological impact assessment of buildings or houses made of brick, concrete or wood. In a majority of them taking into account raw material extraction, wood use shows a far lowest ecological print. The same conclusion comes up with LCA implemented for many other uses of wood (packaging, window/door framing, etc.).
Besides, wood has another important additional asset: it can be recovered and reused for a second, third or fourth utilisation, as industrial plywood panels for i.e. These large possibilities of reusing, recovering or recycling wood work in favour of its ecological balance. Unlike the competitive materials, wood is utile and usable till the far end of the chain by energy production.
Various documents also look into the impact of a direct use of wood as energy source. Wood clearly shows environmental advantages compared to fossil resources and appears to provide cleaner energy, which rejects less noxious gases and with controllable particles emissions. Unlike gas or oil, wood resource is renewable (in the case of appropriate forest management) and the carbon dioxide from combustion is entirely balanced by carbon storage in replanted forests. Energy efficiency seems to depend on combustion systems and wood types, but it is increasing with technical progress. Even though woody biomass resources management and its current competitiveness are still under discussion, it seems wood will constitute a significant part of energy production in Europe in a close future.
2. Advantages and limitations of wood physical properties
Wood has a major advantage in building which is an excellent strength/weight ratio. It has a great capacity to support heavy loads with a small material weight. Some wood composite materials (LVL, glulam) would be at the same time stronger, lighter and more ecological than steel and concrete. Its main disadvantages are dimensional instability and sensitivity to humidity but both could be greatly reduced by appropriate processes.
Wood is also by nature an isolating material with a low conductivity compared to metal or concrete. It does not create thermal bridges in building. In addition it has great hygrometric properties and maintains good indoor air quality. Wood thermal properties are different if one talks about winter or summer comfort. However, with wood and an appropriate design it is easy to reach the isolation objectives of the RT 2005 rules related to energetic performance.
Some documents also contribute to deny preconceive ideas regarding wood behaviour in fire. It is necessary to distinguish fire reaction and resistance. Wood is flammable and combustible. The flames it generates can inflame other indoor materials. Wood itself emits little toxic gases. This reaction depends on the wood species and glues used. Hard and dense woods (oak, beech) catch fire with more difficulty than soft woods (firs, poplars). Wood or wood products’ behaviour in fire can be improved by fire-retardant coating or in mass treatment.
However wood can last a long time under fire. Thanks to its structure it notably has the capacity to keep its strength properties under fire which assures a great stability of buildings. Wood is a solid material and is predictable under fire : its resistance is greater than concrete or bricks which crumble with heat or steel which bends. Thanks to these characteristics, firemen have the authorization to intervene longer under a wood framed building than a concrete or steel structure.
As regards wood durability, old preservation treatments based on chrome and arsenic have been prohibited. Some documents emphasize the existence of various other processes providing with an excellent wood preservation and improvement of mechanical properties (especially hygroscopy and dimensional instability) with no danger for users or environment (oil- or heat-treated wood, etc.). Some species can thus have an extended life-time and are well adapted to outdoor use.
3. Health, well being and consumer appreciation
Several studies tend to refute preconceived ideas on wood hygienic properties which are often considered insufficient, especially for food contact (utensils, packaging). The majority of them demonstrates there is no danger or even an advantage of using wood in comparison with other materials such as PVC or plastics, particularly regarding chemical molecules leakage or the persistence of an active microbial flora.
Finally wood gets a very positive feedback from the consumers whatever the country which constitutes an important commercial asset. It is the case of the survey TNS-SOFRES about French people’s perception of forest and wood, but also results from several scientific studies on positive impression and even physiological effects produced by an indoor environment made of wood.
CONCLUSION
This database open to all on DEFOR website aims to gather technical references and identify various arguments in favour of wood that could be use by the professionals to improve communication and dissemination on their product. Other topics such as maintenance and reparation ease (wood framing) or building yard management rapidity for which scientific information is poor, are not presented here but are significant additional assets in favour of wood use that should be taken into consideration.
The current database will be regularly updated. Thus it should contribute to support the forest wood chain, and the development of more ecological choices in everyday uses.
Sources : On line database
Contact : Christophe ORAZIO, e-mail
Institut Européen de la Forêt Cultivée : www.iefc.net