Sustainable solutions for Dutch housing; reducing the environmental impacts of new and existing houses. Introduction Countless measures for sustainable construction exist, but little is known about the extent of the environmental benefits they offer, or about which measures can best be applied in order to maximise those benefits. Tools to quantify the environmental burden of buildings have now been developed in many countries. However, the results produced by the various tools are not readily comparable. There is no systematic insight into the environmental benefits offered by sustainable construction. Moreover, there is a lack of methods and tools which address the housing stock. To date, sustainable construction and management practice has largely been based on an intuitive approach. This study examines ways in which the environmental impacts of sustainability measures can be quantified, and looks at concepts and strategies for both new-build and renovation projects. Its objective is to gain a better understanding of the environmental benefits offered by sustainable solutions thereof. All stakeholders in the construction sector, including project developers, contractors, local authorities and architects, will then be able to incorporate objective environmental considerations in the planning process. The general research question may be stated as follows: how can the environmental performance of housing in the Netherlands be further improved? The first stage of the study identified the main causes of the environmental burden attributable to new houses, using an environmental analysis of three reference houses: a terraced house, a semi-detached house and a gallery apartment. This enabled various 'priorities' for sustainable construction to be identified. The environmental benefits presented by sustainable construction were then determined by means of a study of four demonstration projects. Furthermore, sets of measures were compiled, the environmental impacts being extrapolated to form seven strategies for sustainable construction. It then became possible to determine which of these strategies offer the best prospects for reducing environmental burden attributable to new construction of housing. No specific tools addressing renovation are currently available. Accordingly, a method was developed to quantify and compare the environmental impacts of interventions in the housing stock. This method is based on the LCA methodology. Two case studies were conducted, both concerning re-differentiation projects in the Netherlands: Morgenstond Midden in The Hague, and Poptahof in Delft. Finally, extensive desk study formed the basis for efforts to chart the role of the factor of time in the LCA methodology. All research findings could then be combined to provide input for a discussion of the current status of methods and tools to quantify environmental impacts. It appeared that serious comments should be made regarding the environmental analyses. Eco-Quantum, a Dutch LCA-based calculation tool, was used to quantify the environmental impacts attributable to material use during construction, maintenance and replacement, as well as those of energy and water consumption during occupation of the dwelling. Because this tool is still in development, two versions were used during the course of the study: Eco-Quantum versions 1.01 and 2.00. Environmental impact of Dutch dwellings; priorities for reduction and benefits of sustainable construction 'Factor 20' represents a very ambitious increase in environmental efficiency with a view to meeting current and future social requirements, i.e. to halve environmental burden assuming a two-fold increase in the world population and a five-fold increase in prosperity. Such an ambition increases the need for quantitative information concerning the environmental benefits offered by sustainable construction. First, the environmental impact of the three reference houses was determined. The houses are typical of the Dutch housing tradition. Table 1 lists the quantities of materials, energy and water used in each housing type. It may be seen that the gallery apartment is relatively material- intensive, while the semi-detached house is responsible for relatively high energy consumption. In nine environmental impact categories, material use contributes more than 50% of the environmental burden, while energy consumption does so in the case of three environmental impact categories. While environmental burden is greater in proportion to the size of the house, the relative contribution of each flow appears to be approximately the same. The main contributors are also identical for each type of house. Fourteen priorities apply in terms of material use: the foundation beams, outer leaves, inner leaves (only applicable to the semi-detached house), window and door frames, glazing, rain proofing in the facades, parting walls, load-bearing walls (terraced house and gallery apartment), ground floor, storey floors, floor overlays (terraced house and semi-detached house), roof construction (sloping for terraced house and semi-detached house, flat for gallery apartment), roof overlay (only for gallery apartment) and heat-generation installation. Not only materials used in large quantities are considered, but also a number which are used in only limited quantities. Five priorities apply to energy consumption: space heating, hot tap water, lighting, ventilation and auxiliary energy. These are all the energy functions. Although gas consumption accounts for some 75% of the overall energy consumption, electricity is the prime contributor to a number of environmental impact categories. Water consumption is not among the priorities, since it is of far less significance than material use and energy consumption. In order to determine whether current sustainable practices are appropriate, a number of measures being used to address three themes within current demonstration projects were projected onto the terraced house. The three themes are: 1) energy saving both by means of installation technology (the Energy balance project in Amersfoort) and constructional measures (energy efficient dwellings in Bakel), 2) reuse and increase of the life span (the 'Respekt' project in Tilburg), and 3) the use of renewable materials ('Ecosolar' in Goes). The environmental benefits provided by the energy-saving approach addressing installations was -lo%, while that addressing constructional measures was 5%. Reuse and increase of the life span provided 5% benefits, and the use of renewable materials accounted for 15%. (A negative percentage indicates an increase in environmental impact rather than any decrease, i.e. a worsening of the situation.) In considering the orders of magnitude, it should be remembered that the differences in each environmental impact category can be very large, varying from a 77% increase in environmental burden to an 81% decrease. The search for the most eco-efficient strategies; Dutch lessons in sustainable housing construction A more systematic approach was used to identify the most eco-efficient strategies for new construction. Four strategies relating to sustainable material use were identified: dematerialisation (MI), material substitution (M2), prolongation of the service lives (M3), and improvement of reusability (M4). Three strategies for sustainable energy consumption apply: avoiding unnecessary energy consumption (E1), use of infinite energy sources (E2) and clean and efficient use of finite energy sources (E3). For each strategy, one or more sets of measures were compiled and the likely impacts calculated, based on current practice and/or technological possibilities. The results of this process are presented in Tables 2 and 3. The strategies of dematerialisation, avoiding unnecessary energy consumption and clean and efficient use of finite energy sources produced a reduction in environmental burden in almost all environmental impacts, but the benefits thus made will be limited in future. In the case of material substitution, improvements in certain environmental impacts are almost always accompanied by a worsening of others. It was concluded that more attention should be devoted to material use in solar-energy systems. The environmental benefits provided by reduced energy consumption are largely obviated by the nature of the materials used. Service life prolongation and reuse are required if significant advances are to be made, although it must be remembered that the environmental benefits remain uncertain, since these will become apparent only in the distant future. It is therefore appropriate to use these two strategies in combination with others. Tools for sustainable housing management: the case of the Netherlands and Finland There are currently three tools for sustainable housing management in use in the Netherlands: Duwon, the National Package for Sustainable Housing Management and Green Investment. These tools give no more than indications of the environmental benefits offered by the management measures applied. In the Netherlands, the emphasis is on the quantifiable aspects of sustainable construction: the tools do not offer any information regarding the qualitative aspects of housing management. The quantitative approach is not in keeping with the management task itself, which comprises the restructuring of mostly post-war residential districts. This demands a more strategic set of tools. Finland has only one tool, still in development, to support sustainable housing management and to provide any indication of environmental benefits: the Environmental Systems Guide for Real Estate Management. This tool takes the qualitative view of environmental benefits. However, the main management task in Finland is that of renovation, for which the quantitative approach would be far more appropriate. LCA-based tools can, in principle, be applied to renovation issues, but the existing tools do not address the strategic considerations. Environmental impacts of interventions in the Dutch housing stock Transformation can fill the gap between no intervention at all (other than maintenance) and demolition and new construction (redevelopment), since the necessary modernisation can be achieved while retaining as much as possible of the existing structures. Transformation is essentially the process of improving the quality of an entire housing complex, across the boundaries of the individual houses it contains (as in combining small houses to become larger houses). Transformation is often seen as more environmentally friendly than demolition. Because there were no methods and tools available to measure and to compare the environmental impacts of such interventions, a new method had to be developed to substantiate this claim. The calculations of the environmental impact of an improved house combined two construction phases, two occupancy phases and two demolition phases, i.e. before and after the improvement process. The environmental impacts attributable to those components demolished and removed during the improvement but still retaining some useful service life was included. In order to compare interventions of different planned service lives, the average annual environmental impacts were used as the basis for comparison. Finally, the comparison of the improvement process with that of demolition and new construction was based on the reconstruction of the houses after the improvement. The method was applied in the two case studies: Morgenstond Midden in The Hague, a 1950s housing development of three-storey and four-storey tenements, and Poptahof in Delft, a 1960s district with high-rise and medium-rise apartment blocks. Both presented good opportunities for transformation, resulting not only in an amended floor plan but in several other improvements such as thermal and sound insulation, and replacement of installations. Although the interventions were extensive, the transformation process represented great savings in material use and waste production compared to demolition and new construction. In Morgenstond Midden, material use was 41% lower and waste production 86% lower. In the case of Poptahof, material use was 62% lower and waste production 91% lower. In both cases, foundation, facades, inner walls and floors accounted for 90% of the material use. Moreover, transformation has resulted in lower energy consumption than in the zero situation (i.e. no intervention at all). In the case of Morgenstond Midden, the environmental benefits attributable to transformation were 0% to 17% compared to the zero situation, while those of demolition and new construction would vary between -9% and 30%. The environmental benefits of transformation as opposed to new construction are largely due to reduced energy consumption. The benefits are, however, smaller than might be expected on the basis of the reductions in material use and energy consumption. This indicates that the building components which are responsible for relatively high environmental impacts have been replaced. In Poptahof, the environmental benefits of transformation were comparable, at 0% to 20%, the only exception being depletion of a-biotic resources, for which burden increased by 9%. Demolition and new construction produces benefits of up to 25% in all environmental impacts. Both material use and energy consumption contribute to the overall environmental benefits. Here too, the environmental benefits are smaller than would be expected based on the reductions in material use and energy consumption achieved. However, the facades of Poptahof had to be replaced in their entirety, and this is the building component with the greatest contribution to most environmental impact categories. In both Morgenstond Midden and Poptahof, transformation of the housing stock may be seen to have produced better environmental performance than demolition and new construction, and better environmental performance than no intervention at all. Between sustainable and durable: optimisation of life spans Durability in the sense of a long service life, and sustainability in the sense of environmental friendliness are often regarded as two separate concepts. There is indeed some conflict of interests, since materials with a long service life may account for greater environmental impacts than those with a shorter service life. Some materials may cause relatively high environmental impacts but nevertheless be more readily reusable than those which cause less impacts but cannot be reused. The optimisation of life spans whereby both durability and sustainability are addressed in tandem can resolve this paradox. Accordingly, an analysis was made of the role of the service life of houses and house components within the overall environmental burden caused by the terraced house. The analysis revealed that the environmental benefits of houses with a longer intended service life decrease in proportion to the extension of that life, although the negative effect of a shorter service life remains greater than the positive effect of a longer service life. Moreover, prolongation of life spans will not always result in less environmental burden. This is due to the actual construction process itself, which accounts for the greatest proportion of overall environmental burden. With regard to the prolongation of the service life of components, it was found that a longer service life has less overall positive effect than a shorter life has overall negative effect. The use of components with longer life spans is clearly most appropriate in buildings which themselves have a longer service life. Recycling and reuse are also aspects of the optimisation of life spans. For example, a short service life can be compensated by the use of materials which are readily reusable. Although there is as yet no scientific basis on which to base the claim, this would tend to promote sustainability in the sense of environmental friendliness. The prolongation of service lives will certainly result in environmental benefits, but is not a decisive factor. The factor of time in Life Cycle Assessment of housing Regardless of the application, the LCA system has certain shortcomings in terms of allocation, weighting, reliability of data, bio-diversity and interference. In the construction sector, the long service life of buildings renders the LCA yet more complex. Besides it introduces many uncertainties. The factor of time is of significance here. Many aspects of the building will change over time. New construction materials and components will be introduced several times, old materials and components will be removed. Even where the replacements are exactly the same as those used in the original construction, innovations and trends will also cause various changes in form and use. Such factors are not currently considered in the LCA. We may therefore identify six aspects of the factor of time, three of which are static: design, redesign and technical service life. The other three are dynamic and relate to future developments: production technology, waste treatment technology and functional service life. In order to gain a complete picture of the environmental impacts of sustainable construction, all aspects must be included in the calculations. Existing knowledge relates mainly to the static aspects. A greater understanding of the role of the other, dynamic aspects of the factor of time may be obtained using scenarios, turning points, sensitivity analyses and potentials. Discussion on the state of the art in quantifying environmental impacts The LCA methodology was introduced in the construction sector as a response to the shortcomings of the tools which listed the materials for certain applications in categories, from 'first preference' to 'to avoid'. These lists were often incompatible or even contradictory. It was also realised that materials and their use should be considered over their entire service life. The step to implementing the LCA at building level was quickly made. One of the tools developed was Eco-Quantum. There have been several versions: Eco-Quantum 1.01 was based on the CML I-method; Eco-Quantum 2.00 is based on the CML 11-method, published some ten years later. CML I1 makes use of the LCA standards developed in the meantime. Calculation of the environmental impacts of the same measure using the two versions produces a disturbing disparity in results. For example, the 52% environmental benefit in terms of depletion of a-biotic resources suggested by Eco-Quantum 1.01 is not reproduced by Eco-Quantum 2.00, while the 45% benefit in aquatic eco-toxicity is reduced to just 8% by the later version. Substantial increases in environmental impacts in terms of depletion of raw materials (55%) ozone depletion (25%), human toxicity (9%) and acidification (8%) are actually reversed to become decreased environmental impacts in depletion of a-biotic resources (8%) and eutrophication (6%). It would appear that the disparities are mostly due to developments in the LCA methodology itself, whereby no distinction is now made between the depletion of raw materials and that of fuels. Depletion of a-biotic resources, human toxicity and eco-toxicity are now subject to completely different calculation methods. The criteria by which ozone depletion and photo-oxidant formation are assessed (comparing the substance having a supposed environmental burden to a reference substance) have also been modified. Changes to the Eco-Quantum method, including those to materials and waste data as well as to normalisation and weighting factors, seem to play a far smaller role. However, Eco-Quantum is not transparent enough to allow identification of all factors which are responsible for the different results produced by versions 1.01 and 2.00. Although the LCA methodology has seen major development over the past ten years, there are still further developments to come. This, together with the long service life of buildings, raises severe doubts concerning the usefulness of quantifying the environmental impacts at the level of the building. It would appear that the methods and tools used are not (yet) robust enough. Conclusions and recommendations In attempting to improve the environmental performance of residential property in the Netherlands yet further, material use and energy consumption are of equal importance. In both cases, the flows themselves do not provide enough information. We must look at the environmental impacts themselves. It would seem that even the materials (e.g. lead and copper) and types of energy (e.g. electricity) which are used in small quantities can have major environmental impacts. Moreover, the differences between the impact categories themselves are large, whereby much information is lost when expressing the overall environmental burden as a single figure. In the case of new construction, one problem is that the short-term environmental benefits will be relatively modest, while the long-term benefits can be substantial. It is therefore imprudent to concentrate solely on the strategies with highest environmental benefits, since these involve too many uncertainties. It is preferable to adopt a broad view of all opportunities for improvement. This study has provided an indication of the potential available, and of the pros and cons of certain strategies, whereupon a reasoned choice of sustainable construction approach can be made. Transformation results in major reductions in material use and the amount of waste produced. However, here too the environmental impacts show a smaller improvement than the flows analysis would suggest. Significant opportunities will be missed if transformation is regarded as offering greater environmental benefits than new construction in every case. The aspect of service life plays a special part in answering the question of how the environmental performance of housing can be improved. Where the prolongation of the service life is adopted as a strategy, it must be remembered that the environmental benefits will only become apparent in the (distant) future and are therefore subject to uncertainty. Moreover, prolongation is not always useful. For example, there is no point in striving for a long service life for components being used in a building which itself has a short (remaining) service life. Achieving an appropriate balance between the service life of components and their host building is therefore something of a challenge. It would seem that the greatest environmental benefits to be had from service life prolongation are those which derive from not having to build a completely new property. However, construction products, construction processes and the nature of the houses themselves are likely to change considerably over time. It is therefore not possible to make any firm conclusions regarding the long-term environmental benefits. A further complication is that the LCA system is not yet fully developed. It is appropriate to devote attention to the concept itself. Quantification of the environmental impacts of houses is useful, but it must be realised that major uncertainties remain. Although the collection of empirical data concerning service lives can increase our understanding of cause and effect, there will always be wide 'bandwidths'. Accordingly, we must not concentrate too much on attempting to remove the uncertainties. This research has produced various recommendations for policy. Firstly, the LCA methodology is too complex to be used as the basis for material-related performance requirements as part of the Dutch Building Decree. It would appear that performance agreements based on the Eco-Quantum system will be of more use to local authorities, although the authorities themselves would prefer to see binding national legislation. Using Eco-Quantum, it would be possible to impose certain requirements not only in terms of material use, but for energy and water consumption as well. Now that the Building Decree itself fails to address environmental issues directly, the government should allow local authorities to impose their own requirements in this area. It remains necessary to encourage the development of calculation tools, although the emphasis must be on their practical applicability. A significant omission is the lack of weighting factors. Preferably, these should be defined at the European or international level, rather than by the national government. Calculation tools can also form the basis for an eco-labelling system, enabling homebuyers and potential tenants to make a more environmentally aware choice. Finally, sustainability must be adopted as an assessment criterion for funding under the Dutch policy instrument Urban Renewal Investment Budget. If this is not the case, the housing stock will be subject only to the policy addressing energy efficiency and renewable energy. The housing stock has great potential to help the Netherlands achieve the targets of the Kyoto Protocol. However, to tap that potential will require increases in gas and oil prices in order to encourage sustainable construction and renovation. Fewer recommendations can be made for practice itself, since the results of the research are subject to certain reservations. Local authorities can try to achieve their sustainability ambitions by means of performance agreements covering residential developments. Project developers can promote sales of sustainable houses by presenting the advantages: lower energy bills, greater comfort and better health. The challenge facing architects is to combine various sustainable construction strategies. To rely on just one strategy is not prudent, since each has both environmental advantages and environmental disadvantages. Contractors must be alert to construction faults, as must installers. The realisation of the great potential of the housing stock is a primary responsibility of housing managers. They must devote greater attention to the choice between improvement on the one hand, and demolition and new construction on the other. The environmental benefits can go further than the retention of the houses. Residents cannot be asked to contribute much to the sustainable construction process. However, resident behaviour should guide the choice of sustainable construction measures. Finally, four recommendations for follow-up research can be made. Firstly, little is known about the influence of resident behaviour and management practice on the environmental benefits of sustainable construction. More research in this area is called for. Secondly, further research is required into the environmental impacts that derive from the location of the property, such as those caused by use of the private car for transport. Thirdly, the experiences to date with LCA of buildings suggest that alternative methods for quantifying the environmental impacts of housing must be sought. The LCA methodology was developed for consumer goods, not for houses. Moreover, it is essential to include the housing stock in any assessment. Knowledge concerning the environmental impacts of interventions in the housing stock is still in its infancy. Fourthly, it seems advisable to develop a model whereby environmental knowledge can be integrated into the planning processes for both new construction and redevelopment.