Workshop 13 - Housing and Urban Processes: Towards Sustainable Communities?
Environmental assessment of buildings: bottlenecks in
current practice
Inge Blom
I.S.Blom@tudelft.nl
Paper presented at the ENHR conference
"Housing in an expanding Europe:
theory, policy, participation and implementation"
Ljubljana, Slovenia
ENHR International Conference, Ljubljana 2006
Workshop 13: Housing and Urban Processes: Towards Sustainable Communities?
Environmental assessment of buildings: bottlenecks in current practice
Inge BlomOTB Research Institute for Housing, Urban and Mobility Studies Delft University of Technology
I.S.Blom@tudelft.nl
Abstract
Ever since the late sixties of the previous century, tools have been developed to be able to quantitatively assess the environmental impacts of products and processes. These tools are based on the Life Cycle Assessment (LCA) method. The original tools were developed to assess production strategies and consumer goods, but now they are being used to assess buildings. However, several problems arise because of the different characteristics of consumer goods and buildings.
In the first part of this paper, the problems that arise are being presented. First, deficiencies in current knowledge on the environment and their implications for an LCA of buildings are described. Second, deficiencies in the building model are discussed. The building model describes the processes and products in the building life cycle that should be taken into account in the environmental assessment. Third, the practical bottlenecks in performing an environmental assessment of buildings are dealt with.
In the second part of the paper, the direction for further research is outlined. Based on calculations which were performed to be able to quickly assess assumptions about the characteristics of the environmental impact of dwellings several possible topics for further research are presented.
1. Introduction
In recent years, many researchers have developed methods to assess the environmental performance of a building with a view to eventually creating a sustainable built environment. Two main environmental assessment method categories can be distinguished: qualitative and quantitative methods (Reijnders and van Roekel, 1999; Udo de Haes, 2000; Forsberg and Malmborg, 2004).
Qualitative assessment methods are based on the relative environmental performance of a building when compared with other buildings or design alternatives (Cole, 1998). The building will be scored on several environmental aspects, such as energy efficiency and land use. The scores are then
weighted and expressed in a single final score. For example, the BREEAM tool rates buildings on a scale of pass, good, very good or excellent (www.BREEAM.org - May 2006). The American LEED system results in a bronze, silver or gold rating (www.usgbc.org - May 2006). Scores may be based on quantitative data, such as energy use, or on experience and common sense. The advantages of a qualitative method are the little amount of time and expertise needed to perform an assessment and the possibility to take into account factors that are hard to quantify, such as land use. On the other hand, there are also some disadvantages. First, it is virtually impossible to rank all technological possibilities for scoring purposes, which means that scoring is based on similar technologies or best available data. Second, it is difficult to define a reference building or a benchmark, since there are so many building categories and design variables. Third, the environmental issues considered are limited. A qualitative tool does not take into account all known environmental problems, which may lead to an oversimplified conclusion. Thus, the level of detail in the assessment results is relatively low. Finally, the results of qualitative tools are not always scientifically valid, because some assessed aspects are based on non validated assumptions and the weighting of scores to obtain a single number result is subjective. Even though qualitative environmental assessment tools will increasingly be based on quantitative data, international consensus exists on the use and development of quantitative environmental assessment tools (Kohler, 1999; Udo de Haes, 2000; Cole et al., 2005).
Quantitative assessment methods are based on an inventory of material and energy flows during the life cycle of a product. The basis of these methods is the closed mass and energy balance: all materials and energy that enter the product system will also leave it, either as a product, waste or as some form of energy. There are two levels at which quantitative methods operate: at the level of general material and energy flows and at the far more detailed level of individual substance flows. Methods operating at the first level are based on the idea that smaller flows are better. Tools that operate on the second level often also contain an impact assessment of the flows of substances from and to the environment. In the impact assessment, the possible contribution of the flows to specific environmental problems is determined. This quantitative assessment method is known as life cycle assessment (LCA). The first advantage of quantitative assessment methods is the possibility to assess the contribution of a product to the full spectrum of environmental problems. Second, it is possible to point out exactly which process is responsible for a high environmental burden so that specific measures can be taken to reduce the environmental burden. A big disadvantage of these methods is the amount of time, expertise and money needed to perform an assessment. Furthermore, the gaps in current knowledge on environmental mechanisms and the limited data availability cause uncertainty in the assessment and its results. Finally, when compared with a qualitative assessment, the results of a quantitative assessment are less comprehensible. Quantitative LCA-based tools for buildings are for example Envest from the UK, EcoQuantum from the Netherlands and the Canadian ATHENA.
In the following sections, a short history of the development of life cycle assessment and its application to buildings is described. Subsequently, section 4 deals with the literature study that was performed with a view to identifying the bottlenecks in the use of LCA for buildings. Section 5 deals
with the case study that was undertaken in order to test some assumptions regarding the life cycle and environmental profile of buildings. Finally, section 6 contains recommendations for further research.
2. A short history of LCA
The development of the life cycle assessment method started in the late sixties of the previous century in the food industry (Hunt and Franklin, 1996; Klöppfer, 1997). The first study was performed by the Coca Cola Company in 1969. Its goal was to analyse the material use, energy demands and environmental consequences of several beverage container alternatives. The study contained all stages from the first extraction of resources from the environment up to and including the processing of waste. In the early seventies, the focus of these assessments was on the reduction of final waste. Because of the energy crisis of 1973, the focus shifted to the reduction of energy use. The results of these early LCA studies were thus expressed as quantities of materials, energy and waste.
As time progressed, LCA was also used to environmentally assess production processes and consumer goods, such as coffee machines. Furthermore, the method was extended in order to be able to assess other environmental effects. An environmental effect is an environmental problem to which the contribution can be determined, expressed in such a way that a larger contribution means a worse effect. Examples of environmental effects are the depletion of the ozone layer or health effects for human beings. However, these additional environmental effects could not be expressed in quantities as easily as the use of materials or the amount of waste produced. Each additional effect requires its own calculation method and has a specific unit in which the results are expressed.
Because of the many ways LCA can be used and the growing number of environmental effects that are taken into account, an international standard for LCA has been developed: the ISO 14040 series. The standard describes the four steps that have to be taken in a life cycle assessment (Fig. 1).
First, the goal and the scope of the study have to be defined. The goal describes the intended use of the results of the assessment, the reason for performing the assessment and with whom the results will be communicated. The goal description also contains a specification of the objects that will be analysed. When the goal is to compare alternatives, the basis of the comparison should also be
Figure 1: LCA framework, ISO 14040 Goal & scope
definition Inventory analysis Impact assessment Interpretation
described. The scope states the geographical and temporal boundaries of the assessment, as well as the quality of the data that should be used. The environmental effects that will be considered are included in the scope of the LCA. A clearly stated goal and scope of the study will help to select the processes and the materials that will or will not be included in the LCA.
The second step in an LCA is to make an inventory of the extraction of substances from and the emission of substances to the environment during the life cycle of the product. These extractions and emissions are called environmental impacts, which are physical changes to the environment. Some studies of fabrication processes only take into account the environmental impacts that happen during the time the product is in the factory, which is called a gate-to-gate assessment. Other studies consider the entire life cycle of the product, which is a to-grave assessment. Recently, cradle-to-cradle studies have been added to these two kinds of studies, because there is no ‘grave’ when a product is recycled.
The third step is the impact analysis. In this step, the contribution of the environmental impacts to environmental effects is determined. It is imported to note that it is not the actual contribution that will be calculated, but the potential contribution to the environmental effects. For example, the contribution of the aggregated emissions of nitrate to all the effects considered is calculated. Even though a single molecule of this substance cannot contribute to more than one effect at the same time, the entire amount of substance emitted is used for each calculation. The reason for this is that it is unknown how the total amount of substance emitted will be divided among the effects. Thus, the potential effect of the impacts is calculated, which is an overestimation of the actual effect. Additionally, usually only the first effect is calculated, not the sequential effects that might occur. As the knowledge on environmental effects progresses, the calculations will become more accurate. The contribution of different substances to an environmental effect can be aggregated using characterisation factors. These factors express the contribution of the substances, related to and expressed in the contribution of a reference substance. For example, the contribution to the global warming effect is expressed in carbon dioxide equivalents.
The fourth step is the interpretation of the results. In this step, the questions that are posed in the goal of the study will be answered by combining the results of the inventory and the impact analysis steps. A sensitivity analysis can be done to assess the influence on the results of assumptions that are made during the assessment.
Nowadays, LCA is also used for large projects, such as buildings. The ISO-standards merely pose the components that an LCA study should contain, which thus far has led to a large amount of tools available. However, the results of these tools are divergent and they sometimes even contradict, which should not be the case (Cole, 2003). Several comparative studies show that it is hard to even compare the tools, let alone the results (Reijnders and Huijbregts, 2000; Erlandsson and Borg, 2003; Forsberg and Malmborg, 2004; Peuportier and Putzeys, 2005).
3. LCA for buildings
In life cycle assessment for buildings, two research areas are involved: the environmental research area and the building research area. The environmental component of LCA consists of the knowledge on environmental mechanisms and the determination of the characterisation factors needed to express the contribution of different substances to an environmental impact in a single unit. The building research area is responsible for describing the object, or the building model, of the assessment. The influence that buildings have on the environment is called the environmental burden. This term suggests that the environmental burden is expressed in a single value, but it actually contains values for al environmental effects considered. Therefore, the term environmental profile is also used.
As explained above, resources and energy are needed to create a building. The extraction of resources and the emission of substances are called environmental impacts. Environmental impacts are physical changes to the environment, but not all changes are per definition harmful for the environment. It is only when the environmental impacts cause unwanted environmental effects that they are considered to be an environmental burden. Unwanted effects can be the change to a less liveable, or a more hostile human habitat, and the reduction in the quality of life at this moment or in the future. It is virtually impossible to assess all the possible effects of the many environmental impacts that occur during the life cycle of a product. This is why the problem is approached from a different angle. First, environmental problems are defined so that the contribution of environmental impacts to these specific problems, or effects, can then be determined. There are two approaches to define environmental problems: the endpoint and the midpoint approach. Each of these approaches uses different indicators to describe the contribution of a product to the environment.
The first approach focuses on the eventual effects of environmental impacts for the human being or ecosystems. The method is thus damage oriented. Environmental effects in this category are for example the loss of biodiversity, loss of health or loss of life years. These effects are called endpoint effects, since they are situated at the end of a chain of subsequent effects. A disadvantage of this method is that quite some assumptions must be made to be able to express the endpoint effects. An important advantage is that the information at endpoint-level is understandable and unambiguous. The second approach focuses on the currently available knowledge of environmental effects that have already been observed and of which the cause is known and quantifiable. Therefore, it is a problem oriented approach. For example, the depletion of the ozone layer is caused by the presence of certain gasses in the atmosphere. The emission of these gasses by a product or process can be determined scientifically. The contribution to the depletion of the ozone layer is an example of a midpoint effect. It is an effect that occurs, but it is not yet directly related to the human being (Fig. 2). The advantage of this approach is the possibility to scientifically validate the results of the LCA and to rule out theories and assumptions. The disadvantage of the method is that the results are hard to communicate, because people tend to have presumptions about for example the further effects of the before mentioned ‘depletion of the ozone layer’ effect.
Currently, the endpoint method EcoIndicator and the midpoint method of the CML centre are joining forces with a view to combining both methods into a single method, in which the indicators
used can be chosen (Guinée, 2000; Heijungs et al., 2003). Currently, both methods use separate calculation methods and use some different assumptions. The object of the joint research is to let the endpoint method be an extension of the midpoint method. Eventually, as knowledge develops, the midpoint effects will shift towards the endpoint effects along the effect chain (Fig. 2).
The methods described above to calculate the environmental burden of a building are a part of the environmental model that is used in a life cycle assessment. The object of the LCA is the building, which is described in the building model. The building model contains the factors that are taken into account in the assessment and the way that the system boundaries are dealt with. A system boundary describes the division of the environmental burden of a process among the multiple output of a process. For example, the environmental burden caused by the production of wooden building components might also partly have to be assigned to the by-products of the process, such as saw dust. In the following section, several bottlenecks in the definition of a building model will be outlined.
environmental impact (emission CFK) midpoint effect (depletion ozone layer) effect effect effect (skin cancer) effect effect
effect endpoint effect
(life years lost)
4 Bottlenecks
Many tools, methods and data are available to perform a life cycle assessment of buildings, each leading to different conclusions which in some cases even contradict. Each tool serves a specific goal, for example to compare design alternatives or to compare the assessed building to other buildings. The available data are usually incomplete and not gathered in a uniform way. Usually, flaws in data are found when an unexpected result occurs.
The LCA methodology is not originally developed for buildings or other large projects, but for consumer goods. Therefore, the assumptions and simplifications made in developing LCA for consumer goods may not be valid for buildings. Four bottlenecks in the use of LCA for buildings can be distinguished. Some of these concern the environmental research area; some are related to the characteristics of the LCA methodology. The simplifications and assumptions in the LCA methodology lead to an overestimation of the environmental burden of the product. An example was already mentioned above in the explanation of the third step of an LCA. For buildings, these simplifications will create a very large error margin (Erlandsson and Borg, 2003).
4.1 Gaps in current knowledge on the environment
The first bottleneck consists of the gaps in current knowledge on the environment and its mechanisms. Although the knowledge is constantly developing, two categories of incomplete information can be distinguished. First, the characterisation factors of substances are not yet known for all substances that are emitted to the environment. New factors are determined and added to the database in the assessment tools. Additionally, the characterisation factors are changed when new knowledge on the environment indicates errors in the already determined factors. Second, the methods to calculate the contribution of environmental impacts to environmental effects develop as well. Moreover, new effects are defined and added to the environmental profile. Regarding these two knowledge categories, the level of uncertainty for the environmental effects is not equal. For some environmental effects, the calculation methods are internationally agreed upon and the characterization factors do not change significantly anymore. Of other effects, the calculation method, characterisation factors or both are still in development or have not been agreed upon. For example, the ‘eco-toxicity marine water’ effect has only recently been separated from the from ‘eco-toxicity fresh water’ effect, which means that the uncertainty level of the contribution to both of these effects is higher than for example the contribution to the ‘depletion of the ozone layer’ effect. However, the distinction between the uncertainty levels is not always clearly stated or considered in the results.
4.2 Omission of temporal and geographical characteristics of environmental impacts
The second bottleneck consists of a simplification of the object of the assessment: the object is ‘frozen’ in space and time. This means that all impacts during the life cycle of the product are assumed to take place at once at a single geographic location. For some environmental effects this assumption is valid, because the effect is global and can only get worse over time. In the first LCA based studies, the environmental effects considered all fitted this profile. An example of such an effect is the depletion of abiotic resources. Over time, environmental effects that did not fit the before mentioned profile were
added to the assessment (Boustead, 1999). These new effects might only occur when a certain concentration of a substance at a certain location is reached. During the life cycle of a product, not all emissions of one substance take place at that location, which might mean that the effect will not occur. Moreover, the emission of the substance might not occur all at once or it may migrate to another of the environmental compartments air, water and soil. If the temporal and geographical characteristics of impacts are not taken into account, a considerable overestimation of effects might be the result. The overestimation of environmental effects might be bigger for buildings than for consumer goods, because the life cycle of a building is longer and the environmental impacts are usually spread around the entire globe. The second bottleneck cannot be eliminated easily, because the knowledge on the migration of substances through the environmental compartments, the risk of exposure to the substances by ecosystems and humans and the effect of the fraction that is taken in is not sufficient yet. This bottleneck is thus linked to the first bottleneck.
4.3 Length of the life cycle of a building
The third bottleneck in the application of LCA to buildings is the long service life of buildings. Typically, an LCA of buildings deals with the entire life cycle of the building and it is performed before the building is actually built. An assumption must then be made about the expected service life of a building. Usually, a technical service life of about 75 years is assumed. However, the actual service life of a building is rather determined by functional and economical standards than by technical standards. The choice of the length of the service life of a building is therefore arbitrary and may influence the results. In the assessment, an end of life scenario of the building will be implemented which describes the way the building will be demolished and how the waste will be processed. This is called an end of life scenario (Udo de Haes, 2001). However, during the service life of a building it is most likely that technology and the state of knowledge will develop. It is not possible to consider new technology in an LCA of buildings because these technologies are not known yet and the building might not be a suitable candidate to use the new technology, for the requirements to apply it are not known at the start of the building life cycle.
Another problem related to the length of the building service life is the much shorter service life of its components. Assumptions must be made on the maintenance and replacement of building components. However, maintenance and replacement depends on the behaviour of the building owner and the building occupant. This means that the environmental effects caused by the building are also dependent from these actors. Currently, the influence of assumptions about the service life of components on the LCA results is being researched.
The length of the service life of the building introduces uncertainties in the modelling of the life cycle of the building. An LCA of buildings should therefore not aim to describe the building life cycle in great detail, but to identify the factors that cause a big part of the environmental effects with a view to replacing or reducing these factors.
The fourth bottleneck is the complexity of the building. According to the ISO 14040 series, the functional unit of the object of assessment should be defined. A functional unit is a description of the object of the assessment in measurable units, which allows for comparison between several objects. For example, the functional unit of a coffee machine might be the amount of coffee it makes in litres. It is very difficult to define the performance of a building. The technical performance of a building can be expressed as a functional unit, such as the thermal insulation of the facades and the roof. However, the functional performance cannot be expressed in measurable units, such as the amount of space, comfort and other aspects related to the perception of the building performance by its users. It is therefore hard to describe the object of assessment (Erlandsson and Borg, 2003). Another issue which relates to the complexity of buildings is the fact that it is virtually impossible to get a closed mass and energy balance in the LCA, which is the basis of this assessment method. Buildings are connected to many other production processes which cannot completely be incorporated in the LCA of the building. Also, there are too many building components to be able to take them all into account.
Concluding, it is impossible to obtain an accurate and complete environmental profile of a building due to the complexity of the ‘product’ and the uncertainties in the life cycle assessment. The goal of an LCA for buildings should therefore not be to obtain such a complete environmental profile, but to gain insight into the largest contributors to environmental problems. This way, the environmental burden of buildings can effectively be reduced.
Case study
As stated above, LCA for buildings should not be used to determine the environmental effects of a building as accurately as possible. However, LCA can be used to identify the factors in the building life cycle that contribute the most to the environmental effects. Subsequently, alternatives for these factors can be developed with a view to reducing the environmental burden caused by buildings. In order to identify the important factors in the building life cycle, a quick case study was performed to test three assumptions about these factors.
The object of the life cycle assessment is one of the Novem reference dwellings, which are descriptions of common building types in the Netherlands (Novem, 2001). In this study, the family house built during the construction period 1980-1988 is used (Fig. 3). The dwelling is inhabited by two adults and one child, which is important for the energy use of the inhabitants. The computer program SimaPro was used for the calculations. In this program, the CML baseline 2000 method was selected (Guinée, 2000). The data are selected from the Dutch Concrete-Environment database, the IVAM-LCA database and the energy data are selected from the ETH-ESU 96 database.
The first assumption is that there is a limited amount of factors that cause the biggest part of the total environmental burden of a building. This assumption was tested separately for the construction and deconstruction phase on the one hand, and the use phase on the other hand. In the construction and deconstruction phase, all the building parts that will be there for the entire service life of the building are taken into account. These building components form the load bearing structure of the building. The assumption proved to be true for 9 out of 10 of the environmental effects considered in
Figure 3: the Novem reference building used in the case study.
the construction and deconstruction phase. For the environmental effects ‘eco-toxicity marine water’, ‘photochemical oxidation’, ‘acidification’ and ‘humane toxicity’, a limited number of materials were the biggest contributors. For ‘depletion ozone layer’, ‘eco-toxicity fresh water’ and ‘terrestrial eco-toxicity’, the biggest contributor was a single category of processes. For ‘depletion abiotic resources’ and ‘global warming’, a combination of a few materials and a process category caused the biggest contribution. Finally, for ‘eutrophication’, no limited number of factors was found. A sensitivity analysis on the assumed transport distances showed that the results did not change for more than 3% when the distance was doubled, except for the global warming effect (6%). It should be noted that the travel distances only concern the distance from the factory or sea port to the building site. The transport that was incorporated in the material and process data could not be changed. When the waste fractions were doubled, the contributions to the environmental effects changed a bit more, ranging from -15%
until plus 11%. The reduced environmental effect after increasing the waste fraction is caused by the re-use of the waste, which results in a prevented environmental effect and thus a negative environmental impact.
In the use phase, building components with a shorter service life than the service life of the building were taken into account, as well as the use of resources by the inhabitants. The environmental profile was calculated on a yearly basis. Thus, a building component with an expected service life of 25 years has been taken into account for 1/25 part of the environmental burden during these 25 years. The resources taken into account are electricity, gas and drinking water. The amount of resources taken into account is the average use of resources by the household in the reference dwelling, which includes energy use by household appliances. The results show that the resources are by far the biggest contributors to the environmental burden for all the environmental effects. Figure 4 shows the relative contribution of the three resources considered. Clearly, the energy use and for some environmental effects the use of gas are important factors in the environmental burden of the dwelling. A sensitivity analysis shows that the results strongly depend on the choice of the service life of components and the amount of resources used. It is therefore necessary to extend research on this part of the life cycle of a building.
Figure 4: relative contribution of resources in the use phase.
The second assumption is that design decisions influence the kind of factors that contribute the most to the environmental burden of buildings. Also, they will influence the total amount of the environmental burden. For example, the biggest contribution to the environmental effects of a brick house will be caused by different factors than a wooden house. Thus, the environmental profile of a building will be partly determined in the design stage of a building. In this study, a comparison is made between three construction methods of a brick house: the traditional stacking of building blocks, on site poured concrete construction and the assembly of prefabricated one storey high concrete building
elements. The comparison between the three construction methods is made exclusively in the construction and deconstruction phases, because only the load bearing building components are different in the three variants. Figure 5 shows the overall comparison between the three construction methods.
Figure 5: comparison between three construction methods.
The differences in the total amount of the environmental burden are caused by differences in the amount of materials and processes used. For both the ‘depletion of abiotic resources’ and the ‘ecotoxicity fresh water’ environmental effects the amount of concrete in the ‘poured concrete’ and ‘prefabricated elements’ construction methods is responsible for the difference. The use of galvanized steel construction parts in the ‘stacked building’ construction method is the cause of the difference in the ‘humane toxicity’ effect.
The biggest contributors in the three construction methods were the same, because the only difference is the amount of materials and processes used. As mentioned above, the important factors are either a limited number of materials, a process category or a combination of both. Possibly, the factors will be different when a comparison is made between dwellings that use different materials and processes. The result of the ‘humane toxicity’ effect shows that a relatively small amount of a material can have a large effect. Thus, building materials cannot be excluded from the analysis based on their volume.
The third assumption is related to the building life cycle. The assumption is that the environmental burden caused in the use phase of a dwelling, from the first use until the final deconstruction of the dwelling, is much higher than the environmental burden in the construction and deconstruction phases
when compared with the total environmental burden caused in the Netherlands. To test this assumption, the environmental burden of the construction phase of the stacked building variant was multiplied by 65,000, which is the amount of buildings built annually in the Netherlands. The environmental burden in the use phase was multiplied by 6,850,000, which is the amount of households in the Netherlands. Both numbers where then related to the total environmental burden in the Netherlands in 1997. The results are shown in Table 1.
Environmental effect Construction phase [%]
Use phase [%]
Total [%]
Depletion abiotic resources 0.07 1.88 1.95
Global warming potential 0.41 9.77 10.18
Depletion ozone layer 0.00 0.12 0.12
Humane toxicity 0.28 1.43 1.71
Eco-toxicity fresh water 0.13 2.80 2.93
Eco-toxicity marine water 76.9 57.1 134
Terrestrial eco-toxicity 0.07 0.85 0.92
Photochemical oxidation 0.51 0.28 0.79
Acidification 0.87 3.11 3.98
Eutrophication 0.01 0.18 0.19
Table 1: relative contribution of dwellings to the total environmental burden in the Netherlands.
These results are merely meant to indicate the possible importance of the use phase when compared with the construction phase. Of course, not all buildings are the same as the reference building and not all households have the same resource consumption pattern. Additionally, not all building components were taken into account and the level of detail of the study was too low to be conclusive. The result on the ‘eco-toxicity marine water’ effect is caused by the fact that this effect has only recently been added to the environmental assessment method and the calculation methods are not correct yet. This result is therefore caused by an error in the software. The other results indicate the relative importance of the use phase might indeed be higher than the construction phase.
Further research
Further research in the field of the quantitative environmental assessment of buildings should focus on several issues. In general, the focus should not only be on the building as a product consisting of building materials and the use of energy for climate control, but also on the people that influence the environmental performance of the building, such as the designers, occupants and owners of buildings. Additionally, assessment methods should be developed for dwellings as well as for public, industrial and commercial buildings.
The first focus of further research should be the development of a comprehensive and usable database structure for environmental data on materials and processes. The currently available data are not consistently gathered and the origin of the data is not always clear. Furthermore, the level of detail in the data is not always sufficient. A data gathering and storing format should be developed and if possible transport, energy and waste data should be separated from other processes with a view to regarding the influence of these factors separately. Additionally, the database should be easy to
maintain and update, which should be done regularly. The Swiss EcoInvent has developed the EcoSpold data format which is a first step (Hedemann and Meinshausen, 2003).
Second, a model of the building as the object of a quantitative environmental assessment should be developed. Possibly, a separate model for the major phases in the building life cycle is appropriate because of the different characteristics of the environmental profile and the differences in the major contributors to the environmental effects in each phase.
Third, further research should focus on the use phase of the building life cycle, because there are much more buildings than the amount of buildings constructed each year and therefore this phase might be an important part of the annual total environmental effects caused by buildings (Blom, 2006). Insight is needed in the influence of occupants on the environmental effects and data should be gathered on the period of use (Reijnders and van Roekel, 1999). For example, empirical data on the maintenance of buildings, building components and building services as well as data on behaviour and decisions of occupants and owners should be gathered.
Fourth, the influence of other design decisions than the construction method on the factors which cause the biggest part of the environmental effects should be determined. Other design decisions include the kind of dwellings, such as flats or villas, the use of passive solar energy or the kind of materials used. Based on the case study, decisions that affect the kind of materials and processes used are most likely to result in different important factors. If only the amount of materials and processes change, the same factors will be important in the total environmental burden of the building.
Finally, possible ways of performing an environmental assessment of transformation and renovation of buildings should be explored (Klunder, 2005).
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