Discussion and conclusion

In this section an attempt is made to conduct ecological comparisons between products from wood as the major raw material and those from other materials. The selection of products to be compared is related to housing and other buildings. The study covers four product groups: single-family houses, large buildings, window frames and flooring materials. The results obtained show only a very general view of the ecological behaviour of the products concerned.

The environmental impact categories taken into account are "Global Warming Potential", "Acidification Potential", "Eutrophication Potential" and "Photochemical Ozone Creation Potential". There are also other important impact categories such as human toxicity, eco-toxicity and resource depletion that have not been included in this study. Regarding the resource availability/depletion, a brief description is given in section "Resources availability".

Data for the conduction of this study were collected from different literature sources covering energy and LCI studies as well as LCA reports. In order to determine the impact assessment for all product groups in the same way, only data for LCI and energy were taken from the literature. However, the calculation of the impact potentials mentioned above were carried out within the framework of this study by using GaBi 3.0 software program.

It is important to mention that some reports cited only give the energy consumption and material input, e.g. Damberger study (1995), whereas some others show only the energy input, e.g. Forintek Canada Corporation 1991, Baier (1982) quoted from Burschel et al. (1993) and BM-BAU (1993). For this reason, data on LCI, particularly material input, are not found for sheds and three-storey buildings, but are found for other groups in this report.

Goal and scope of LCA studies

The ISO 14040 prescribes the clear definition of the goal and scope at the beginning of all LCA studies. The goal of an LCA study shall unambiguously state the intended application, the reason for carrying out the study and the intended audience, i.e. to whom the results of the study are intended to be communicated.

The scope includes among others the description of the functions of the product system, or in the case of comparative studies the systems, functional unit, product system and product system boundaries, type of impact, allocation procedures, data requirements and data quality, assumptions and limitations.

Both goal and scope influence the conduction and the later application of an LCA study. All LCA studies conducted and/or cited in this report must also fulfil the requirements of ISO 14040 by comparing buildings made of different construction materials with the same functional units and system boundaries. An LCA including only two or three life cycle phases shall not be compared with another LCA which considers the entire life cycle.

The product groups used in this study are single-family houses, large buildings, window frames and flooring materials and, within a product group, LCA have the same goal and scope. However, different product groups might have different definitions of goals and scopes and, therefore, results of LCA can only be compared for products within one of the above-defined product groups. In any case, goals and scopes as defined in the original reports will have to be considered.

Finally, one has to distinguish between products made of solid wood and those made of a combination of wood and other materials. Wood flooring, parquet, window frames, blockhouse and three-storey building made of solid wood are wood products. Other materials used for their manufacture or construction can be specified as more or less supporting materials. On the other hand, the timber-frame house and the wooden window are not pure wood products because besides wood other component materials are also quantitatively important. The products investigated in this study are specified as follows:

• Non-wood products: Products that do not contain wood as raw material but perhaps as a supporting material which is quantitatively unimportant.

• Mixed products: Products that contain various raw materials of which wood is quantitatively an important part.

• Wood products: Products that contain wood as raw material.

Supporting wood materials in non-wood products are not considered to be recycled or thermally utilized. They are also not included in the CO₂-related aspects.

Resources availability

Generally, there are renewable and non-renewable resources and wood belongs to renewable materials, whereas fossil fuels are amongst the non-renewable materials. Based on the principles of sustainability, it is possible to produce wood as biomass and secure the permanent availability of this important material. Except for fossil fuels, the non-renewable resources can also become permanently available through recycling but it depends very much on an economically acceptable and ecologically sound recycling technology.

The quantification of the potential resources availability is not part of this study. Additional efforts are necessary to achieve a reliable judgement on the future availability of finite raw materials dealt in this study. The only way for comparing wood with non-renewable material is suggested by Frühwald et al. (1997) in the following qualitative description.

The existing resources are classified in categories:

In many countries efforts have been made to improve sustainable forest management systems, and wood from these areas can be regarded as very favourable material. Furthermore, in comparison with products made of non-renewable material, similar products from wood should be preferred.

For some inorganic and synthetic materials (metals, PVC, etc.) recycling technologies have already been developed and products from these materials might be specified as favourable provided that recycling takes place and the technology applied is at least environmentally sound.

Thermal utilization of waste wood

The life cycle analysis of single-family houses and other buildings have shown that the thermal utilization of waste wood contributes considerably to the reduction of environmental impacts. Similar effects can also be achieved if wooden parts of other products are utilized for energy generation. The carbon cycle in wood and other renewable material (biomass) can be described as follows.

Generally, in a sustainable management system the vegetation withdraws carbon dioxide from the atmosphere through the process of photosynthesis. Burning of wood or decomposition by micro-organisms results in a reverse process where carbon dioxide and water is released, therefore, photosynthesis, use and burning/decomposition of wood form a closed carbon cycle. The solar energy collected by the photosynthesis is released by burning (18.9 MJ/kg oven-dry material). Therefore, the energy from wood and other biomass can be regarded as solar energy.

For the environmental impact assessment of single-family houses, three-storey buildings and sheds, two cases are analysed: no thermal utilization of waste wood (Case A) and thermal utilization of waste wood (Case B). Both cases have been described in detail in sections "LCA of single-family houses" and "LCA of simple large buildings" and the results demonstrate two facts which are particularly beneficial to the environment (compare also with Table 20):

• Less fossil energy is needed for wood-based houses and buildings (Case A and Case B).

• The more the volume of waste wood, the more renewable energy can substitute fossil energy so that the net fossil energy consumption is considerably reduced (Case B).

These facts are not only valid for the objects mentioned above, but also for many other products of which a considerable part is made of wood (e.g. windows, flooring materials, furniture, etc.).

Table 20: Environmental benefits of wood as construction timber and as fuel

Windows

Wood frames show, in comparison with other window types, the lowest weight and consequently the minimum environmental impact resulting from transportation. The k-value is for the aluminium window higher than for wood and PVC windows and therefore the latter ones have better insulation properties than the aluminium window (see also Table 11).

The analysis of single life cycle phases results as follows:

• Concerning the greenhouse effect, the lifetime is the most crucial phase for the wooden window. As shown in Figure 26, the GWP of the lifetime is for the wooden window higher than for aluminium and PVC windows. The reason for this phenomenon is the fact that wood frame is treated at least three times (every 10 years) with paints, lacquers or other chemicals and consequently the more the treatment the higher is the greenhouse effect and GWP.

• Only for wood as frame material the energy and the corresponding GWP are negative (Figure 26). This is a very positive aspect for wood because the energy that can be generated from the frame material at the end of life cycle is higher than the energy consumed at the preliminary stages.

• Transport and lifetime have major influence on AP, EP and POCP in all window types, but due to the shorter transport distances and lower weight, the negative effects of the wooden window is the lowest (Figures 27, 28 and 29).

• For the categories concerned (GWP, AP, EP and POCP), the production phase and its environmental impacts is also important and the effect of aluminium and PVC window is considerably higher than that for the wooden window (Figures 27, 28 and 29).

Flooring materials

For comparing different flooring materials, the results of two studies were analysed, the study of Åsa Jönsson (1995) on different flooring materials and that of Werner and Richter (1997) on different parquet types, but the comparison of the products of the two studies is not feasible due to the following:

• Åsa Jönsson used the EPS Method (Environment Priority Strategy in Product Design) and the Environmental Theme Method.

• The study of Werner and Richter was conducted on the basis of ISO 14040-43.

• Åsa Jönsson compared wood, PVC and linoleum with each other.

• Werner and Richter investigated mosaic solid parquet, two-layer prefabricated parquet and three-layer prefabricated parquet (all out of wood).

Each study is therefore dealt with separately and in detail in sections "Wood, PVC and linoleum as flooring materials" and "Parquet" and the results conclude:

• Ecologically, wood flooring is to be preferred to PVC and linoleum, particularly if resource availability/depletion is included in the analysis of impact categories.

• Regarding the environmental behaviour of different parquet types, the mosaic solid parquet should have the priority.

Reasons for substitution

The results of the comparative LCA studies clearly indicate that wood products and products systems show advantages in most environmental impact categories. This positive result is not surprising for wood technologists and LCA experts with timber-related background. The subjective impression that wood products are with respect to the environmental aspects better than the competitive products can be scientifically proved.

As mentioned in section "Life cycle assessment", the environmental aspects have become more important during the last decade and the question which can be raised in this contexts is: Why do wood products still have to face strong substitution pressure?

There are many reasons. First of all, the environmental behaviour is not the only aspect that influences the decision for or against a product. Other features, such as technical behaviour, regulations (standards, building codes, fire protection directives, etc.), durability, image, habits and, last but not least, product cost, heavily affect the decision.

Due to the favourable environmental aspects, wood products have been enjoying a high customer reputation causing some friction with the other competitors. The positive image of wood was somehow subjective because it could not be quantified and proved by facts. The development of the LCA methodology in the early 1990s has enabled the quantification of various environmental categories and the provision of facts necessary to show the environmental advantages of wood and wood-based products.

The LCA methodology was particularly used by those industrial sectors which did not have such a positive image as the timber sector. They tried to use LCA to prove their environmental superiority. The activities of ISO/Technical Committee 207/Subcommittee 5 concerning the standardization of the LCA methodology was heavily influenced and driven by the chemical industry. Forestry and forest products industry realized rather late the chances and the risks linked to the LCA application. The forestry and the timber sector had the opportunity to use the LCA results as evidence of the superiority of wood over competing products (chances). On the other hand, it could already be too late for LCA-related activities (risks). While the industrial sectors, which are dominated by financially powerful multinational companies, recognized the chances in LCA at the early stages, the widely scattered forestry and forest products industry did not even see the necessity to invest time and financial resources in the provision of LCA relevant data. It took the forest products industry quite a long time and many efforts to overcome the situation.

As mentioned above, the decision to chose a certain product is not only based on environmental aspects. Wood-based products also have some disadvantages. They shrink and swell, are prone to biological attack which may end in total deterioration, need continuous attention and maintenance and can burn. Customers may rate such behaviour very differently and also the cost effects should be considered.

In order to understand better why wood products still have to face substitution pressure, the following list of preferences in a decision-making process of many customers should be considered:

•Regulations often direct the decision in a certain way and this can hardly be influenced by the customer. An example of such an obstacle is the fire hazard regulations in many countries, which prohibit or restrict the use of wood in many building types.

Necessary measures: Work towards wood-friendly building codes, wherever this is necessary and reasonable.

• Technical superiority is very important when it comes to decision-making. Customers tend to chose the technically best and most durable solution when ever the costs for this solution are still reasonable.

Necessary measures: Design wood products and product systems technically sound so that they will be in service for a long time. Low durability and high maintenance efforts will negatively affect the image of wood and the customers' perception in the long term.

• Wood products and product systems must be cost-effective and competitive. Higher prices for wood products compared to competing products can only be justified if there are other features, such as a very positive image, aesthetics, technical superiority (e.g. better insulation properties), which are rated high by the customers.

Necessary measures: Produce cost-effective wood products in order to be competitive.

• The knowledge about the advantages of using wood in constructions is rather limited. This is not only the case for architects, also the end users often do not know enough about wood. This limited knowledge often leads to the wrong utilization of wood and consequently to problems which negatively affect the image of wood.

Necessary measures: Provide easy to use and understandable technical information to architects and end users. Advertise the advantages of wood in an appropriate way.

• Many environmentalists still believe that trees should stay in the forest in order to preserve nature. Certainly, environmental preservation is an important task, but there are environmentally sound forest management systems which secure sustainable utilization of forests without endangering nature.

Necessary measures: Inform environmentalists and politicians about environmentally sound forest management systems and possibilities for sustainable utilization of renewable resources.