4 Scenarios
Context
The current situation in housing construction is characterized by a clear decline in the rate of housing unit completions over the last few years. The construction of multi-storey apartments has been affected particularly severely. Housing unit completions initially rose in the 1990s to the very high level of 600,000 housing units per year in the middle of the decade. This dropped to approx. 400,000 housing units in the year 2001. This decline can be observed in both the Old Laender (western) and the New Laender (eastern). The causes of the very high levels of activity in the area of new-build housing in the last decade of the 20th century were:
• The need to catch up with demand in the Old Laender and New Laender (housing shortage)
• Major influxes of immigrants to Germany
• A series of high-birthrate cohorts reaching the household establishment phase.
A level of new building as high as that of the 1990s will not happen again within the next 25 years. It is likely that the annual rate of housing unit completions during this period will be between 300,000 and 400,000 units. This is attributable to the major housing oversupply in many regions (particularly the New Laender) and, not least, the expected demographic trend in Germany which in the medium to long term will exhibit a strong flattening off or stagnation of population statistics and numbers of households.
The scenarios
In consultation between the project partners, the German Federal Environmental Agency and the members of the advisory panel, two different scenarios were put forward for the construction and housing sector – a reference scenario and a sustainability scenario. The scenario period covers the years 2001 to 2025 (baseline year: 2000). These two scenarios are used to illustrate possible courses of development, and the difference between them makes it possible to identify where there is scope for intervention to stimulate sustainable, environmentally sound construction and housing. This captures the range of possible developments in the construction and housing sector. Calculating the consumption of environmental resources associated with each of the two scenarios yields an idea of trends relating to key indicators such as land take, greenhouse gas emissions or raw materials consumption. From this it becomes clear to what extent, and at what cost, environmental sustainability targets in the construction and housing sector are achievable.
In line with these objectives, the reference scenario assumes the continuation of past trends in the “construction and housing” sector without any real intervention. The
sustainability scenario is based on the same demographic and macroeconomic assumptions as the reference scenario. The critical difference is in the assumption that sustainable construction and housing have gained a high priority for society, that the underlying conditions have been modified accordingly, resulting in higher thermal performance standards in housing, among other things. This will require:
• The upgrading of housing stocks through retrofitting, modernization and aggregation of units
• Accelerated programmes of urban regeneration
• The promotion of land-efficient forms of development
• A consistent policy of using available vacant sites or brown fields
• Establishment of the passive-house thermal performance standard in the mass market
• Consistent promotion of thermal upgrading of the housing stock
• An increase in the proportion of biomass and solar power and of district and neighbourhood heating systems used to supply space heat
• The use of more recycled grit and sand in concrete
• The use of more regenerating raw materials in construction
• Construction without cellars and investment of the resulting cost savings in improved energy standards etc.
Taken together, these approaches map out a vision of sustainable construction and housing, characterizing the course that needs to be taken to fulfil the sustainable development brief. A course for more sustainable development in the construction and housing sector can be set on various levels. These range from the choice of particular construction methods and materials and of different forms of housing (single-family house or multi-storey apartments) to the relative priority given to inner-urban and greenfield site development, or to housing stock upgrading and new construction. The scenarios were structured by way of scenario assumptions on these different levels. These represent the ‘points of leverage’ which influence differences in development leading to different results from the scenario calculations. These
‘levers’ cannot be adjusted ad infinitum. In order to gain a realistic assessment of the extent to which these values can be influenced, work was done with the advisory panel and by means of expert surveys to determine the potential scope, and mechanisms for achieving this potential were also discussed.
The following overview presents key ‘leverage points’ and measures for influencing them:
Table 4.1 Key leverage points for sustainable construction and housing
Leverage points Measures
Extent of new-build Full activation of housing stock (upgrading, aggregation of units) prevents property disuse/demolition, and curbs demand for new-build Distribution of new-build across
‘region type’ categories
Promotion of urban regeneration reins in the trend towards suburbanization
Distribution of new-build across
‘housing type’ categories
More multi-family housing through increased development in built-up areas and promotion of urban regeneration, leading to a reduction in single-family houses
Ratio of inner-urban to greenfield site new-build
Consistent policy of fully utilizing available potential5 and realization of the ‘ExWoSt’ (experimental housing and urban planning programme) conditions6 for the ratio of inner-urban to greenfield development = 3 : 1 Demolition/conversion/aggregation of
old housing units
Improved housing stock maintenance policy
Energy standards for new-build housing
Greater political backing for initiatives promoting housing built to passive-house standards
Advances in heating structures for new-build and existing housing stock
Strong promotion of biomass use (wood pellets etc.) as a renewable energy source, and increase in the proportion of space heat supplied by district and neighbourhood heating systems
Insulation retrofitting in the housing stock
Achievement of the technically feasible insulation retrofitting rate and quality (according to IWU, Institute for Housing and Environment) by increasing state support
Concrete recycling (for use in building construction)
Full utilization of potential in accordance with the “Concrete with recycled aggregate” standard of the German Committee for Reinforced Concrete (DAfStb).
Proportion of wood as a construction material in new single- and two-family houses
Comprehensive promotion of the use of regenerating raw materials, more houses built to passive-house standard (increase in wood as a
construction material)
Proportion of new-build with cellars One aspect of low-cost building, cost savings put to use for improving energy standards etc.
5 Apel, D.; Böhme, C.; Meyer, U.; Preisler-Holl, L.; Szenarien und Potentiale einer nachhaltig flächensparenden und landschaftsschonenden Siedlungsentwicklung [Scenarios and potentials of housing development which sustainably minimizes land consumption and landscape degradation]. German Institute of Urban Affairs (difu) commissioned by the German Federal Environmental Agency.
6 ExWoSt = Experimenteller Wohnungs- und Städtebau, Förderprogramm (experimental housing and urban planning programme), programme funded by the Federal Ministry of Transport, Construction and Housing.
For all of these ‘leverage points’ it is possible to quantify the development of the associated underlying factors (number of housing units, absolute figures and for specific region types; number of housing units with retrofitted insulation; number of passive-houses, etc.). In consultation with the advisory panel, such quantified scenario assumptions were agreed for every “leverage point”.7 In the course of the advisory panel’s discussions, the assumptions agreed upon to differentiate the reference scenario from the sustainability scenario were selected so as to be achievable, given sufficient political will and popular acceptance of the German federal government’s sustainability targets.
The course of development under the sustainability scenario is not conditional upon unreasonable demands that people should moderate or relinquish their material aspirations. However it does depend upon certain reorientations, for instance away from greenfield sites and towards the core built-up areas, or away from new-build housing and towards maintaining the building stock. Overall the assumptions underlying the sustainability scenario result in a clear improvement in the housing stock in Germany. In this scenario, the living space per head rises from around 40 m2/person in the year 2000 to approx. 47 m2/person by the year 2025.8 At the same time, on the assumption of a significant increase in upgrading and modernization of the building stock, a substantial improvement in structural quality can be expected.
7 A complete description of the scenario assumptions, including quantified data, can be found in the final report.
8 Under the reference scenario, in the year 2025 the average living space of approx. 48 m2/person is only marginally higher, but on average buildings are of lower structural quality.
5 Results
The scenario results obtained by applying the new BASiS-2 material-flow model to the scenario period 2001 – 2025 (baseline year: 2000) differ over time, especially when the reference scenario is compared with the sustainability scenario. Selected results are presented below for the key challenges in the construction and housing sector, namely: land and raw material appropriation, climate protection, and arisings of construction debris.
Land use
The daily land take (net site area + access road/path area) in the baseline year 2000 was around 31 ha/day. For the year 2025, the value obtained under the reference scenario was approx 27 ha/day. This contrasts with a land take of only 5 ha/day for 2025 under the sustainability scenario. The figures cited only take account of land use on greenfield sites, i.e. they do not include building within built-up areas (e.g.
infill development).
Figure 5.1 Reference scenario: Land take (net site area and access road/path area) in ha/day for greenfield development in Germany
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00
2000 2005 2010 2015 2020 2025
Year
ha/day
Agglomeration Suburban Rural
Figure 5.2 Sustainability scenario: Land take (net site area and access road/path area) in ha/day for greenfield development in Germany
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00
2000 2005 2010 2015 2020 2025
Year
ha/day
Agglomeration Suburban Rural
This means that under the sustainability scenario, the daily land take falls by the year 2020 to approx. 1/6 of the baseline figure. This would reduce daily land take on a scale commensurate with the national sustainability strategy target for conservation of open spaces.9 Key approaches for implementing the sustainability scenario include efficient use of the building stock, thus avoiding new building; a refocusing of demand for detached single-family houses towards space-saving forms of building (multi-family, terraced) and greater emphasis on development within built-up residential areas (infill development and conversion of vacant sites or brown fields).
Raw materials consumption
Under the reference scenario, the consumption of mineral raw materials (gravel, sand, clay/marl, limestone, gypsum, natural stone/quarrystone) falls only slightly between the years 2000 and 2025, from 269 million t/a to 246 million t/a. Under the sustainability scenario, a decrease of around 33% to 180 million t/a occurs. Beside the approaches already mentioned above, the reduction in consumption of mineral raw materials under the sustainability scenario is attributable to greater use of recycled concrete. Detailed analysis of the results showed that the infrastructure taken into account is responsible for a large proportion of the mineral raw materials
9 The German federal government’s environmental target for daily land-take for new settlement and transportation areas, with the year 2000 as the baseline year (approx. 129 ha/day) anticipates a reduction to around ¼ of the baseline figure by the year 2020 (Perspektiven für Deutschland – unsere Strategie für eine nachhaltige Entwicklung [Perspectives for Germany – our strategy for sustainable development], German Federal Government 2002).
consumed (around 120 million t in the baseline year). Since the bulk of mineral raw materials consumed in the ‘infrastructure’ sub-segment is used for maintenance – approx. 85 million t – and these costs of maintaining the infrastructure will have to be met on an annual basis in future under both scenarios, the overall results under the sustainability scenario show raw materials consumption decreasing less drastically than land take by the year 2025.
Figure 5.3 Consumption of mineral raw materials for construction and housing in Germany (reference and sustainability scenario)
0.0 50.0 100.0 150.0 200.0 250.0
2000 2005 2010 2015 2020 2025
Year
t millions
Reference Sustainability
Climate protection
Under the sustainability scenario, there is a 52% drop in emissions of the greenhouse gas carbon dioxide for the ‘construction and housing’ area of need10 as opposed to around 19% under the reference scenario.
10 These figures take into account the energy consumption for heating the buildings, construction and maintenance of buildings and infrastructure including inputs in upstream chains.
Figure 5.4 Trend in carbon dioxide emissions for the construction and housing area of need (year 2000 = 100%)
0 20 40 60 80 100
2000 2005 2010 2015 2020 2025 Year
% Reference
Sustainability
The results for the trend in CO2 emissions in the construction and housing sector under the sustainability scenario by the year 2020 (- 46%) and by the year 2025 (- 52%), in relation to the year 2000, can be seen as an important contribution of this area of need towards meeting the medium- and long-term climate protection targets11 for Germany as a whole (- 80% by 2050 for national CO2 emissions, i.e. - 40% by 2020 and - 50% by 2030, both in relation to 1990).12 Under the reference scenario in contrast, despite the reduction in CO2 emissions, the result shows that the available potential for making the necessary reductions to meet medium and long-term climate protection targets is not exploited sufficiently.
Since even under the sustainability scenario, Germany’s whole year-2000 building stock will not have been fully upgraded by the year 2025,13 leaving some further potential for reduction of carbon dioxide emissions, here a long-term perspective extending beyond the year 2025 is identifiable. The results of the sustainability scenario, which are essentially based on vigorous thermal insulation of the building
11 No comparison was made between the scenario results and the national reduction target for carbon dioxide emissions (- 25% by 2005 in relation to 1990 levels) since the greater part of the action period for the environmental target had already elapsed in the initial year (2000) of the scenarios. In contrast it is worthwhile to compare the scenario results as regards long-term climate protection targets.
12 The long-term climate protection target is based on the work of the 12th German Bundestag’s Study Commission on “Protection of the Earth’s atmosphere” and relates to total national carbon dioxide emissions.
The 14th German Bundestag’s Study Commission on "Sustainable energy supply under the conditions of globalization and liberalization" (Enquete 2003) also set nationwide CO2 emissions reduction targets of 40%
by the year 2020, 50% by 2030 and 80% by 2050 (all in relation to 1990).
13 In the year 2025, taking into consideration the amount of housing stock upgraded and the cumulative retirement of units (except through aggregation of units, since such living spaces must still be heated), under the sustainability scenario the housing units with potential for future upgrading runs at around 33%, i.e. one-third of the year-2000 housing stock could still benefit from thermal upgrading after the scenario period.
stock coupled with reorientation of the mix of heating towards renewable energies and district and neighbourhood heating, show that longer-term CO2 reduction targets are also feasible if these approaches are adopted.
Arisings of construction debris
The following graph shows the arisings of construction debris14 from housing maintenance and demolition and infrastructure maintenance15 to residential access areas (material excavated from roads, old sewerage pipes etc.). The bar on the left shows that in the baseline year 2000, almost 120 million t of construction debris occurred. The largest share of this is caused by infrastructure maintenance. The next largest share results from maintenance of the building stock. The demolition of housing only accounts for 5 million t of debris in the baseline year.
Under the reference scenario, arisings of construction debris grow to almost 140 million t/a by the year 2025. The factor responsible for this is a large increase in the volume of construction debris resulting from housing demolition programmes proceeding at an accelerating pace. From approx. 5 million t in the baseline year, arisings of construction debris increase to almost 28 million t by the year 2025. In contrast, under the sustainability scenario the level of construction debris remains largely constant. The increase in debris from housing demolition is only on a moderate scale in comparison to the reference scenario.
14 The term ‘construction debris’ also subsumes waste material generated from infrastructure works. In the waste management sector this is normally categorized as ‘road excavation material’.
15 Infrastructure demolition in the sense of total removal (as in building demolition) is not assumed in the scenarios, since in practice this is not a significant factor.
Figure 5.5 Arisings of construction debris from maintenance and demolition of housing and maintenance of technical infrastructure in Germany (reference and sustainability scenario)
0 20 40 60 80 100 120 140 160
Year 2000 Ref-2025 Sust.-2025
t millions
Infrastructure maintenance Housing maintenance Housing demolition
The selected results give a striking illustration of the different directions that development of the construction and housing sector might take. The BASiS-2 material-flow model was used successfully to calculate numerous other results and to analyse them in detail. The complete results are documented in the final report.
6 Perspectives for sustainable construction and housing
With reference to the scenario results, it has been possible to quantify major potential in the construction and housing sector for reducing the environmental impacts of land take, energy consumption, raw materials consumption, debris generation and greenhouse gas emissions. It has been shown that resource-efficient construction and housing coupled with improvement of the supply of housing is a realistic prospect if the assumptions of the sustainability scenario are used as a basis. The quantified results and intensive discussions with the actors on the advisory panel and in the expert workshops enable us to make the following recommendations for action. For sustainable development in the construction and housing sector, the following cornerstones are especially relevant:
• More efficient use of the housing stock by means of intensified rehabilitation (insulation retrofitting etc.) and substantial upgrading (enlarging unit size within the stock by aggregating units)
• Promotion of greater emphasis on development in built-up areas (infill development, activation of vacant sites or brown fields) in parallel with regeneration of town centres, particularly in core cities (thus reducing city exodus).
• Promotion of the use of regenerating raw materials, such as wood, for construction and space heating
• Promotion of the use of district/neighbourhood heating for space heating
• Greater effort to promote the use of recycled building materials (e.g. concrete with recycled aggregates) to conserve non-renewable mineral raw materials.
To this end, significantly greater effort will be necessary on the part of policymakers and all other actors involved in the area of need, if the targets of the national sustainability strategy are to be achieved.16 The actors on the advisory panel and in the expert workshops engaged in detailed discussions of the conceivable mechanisms and measures for furthering the necessary framework for sustainable construction and housing. The most important and most interesting mechanisms and measures17 favoured by the actors in these discourses are presented in association with the corresponding ‘leverage points’ in the following table:
16 Cf. the results of the reference scenario, in which key environmental targets are not achieved (cf. final report, chapter 6.5).
17 Cf. chapter 7 of the final report.
Table 6.1 Measures and mechanisms for sustainable construction and housing
‘Leverage point’ Mechanisms and measures
Extent of new-build Changes to subsidy regime for housing construction, reform of the owner-occupied homes premium
Distribution of new-build across
‘region type’ categories
More incentive levies on private cars (making ‘city exodus’ more expensive), redirection of economic support and regional structural policy towards housing policy goals, environment-related taxation on land value and land area
Distribution of new-build across
‘housing type’ categories
Environment-related taxes on land value and land area
Ratio of inner-urban to greenfield site new-build
Replacement of the land purchase tax with a land consumption tax with a behaviour-modifying effect in terms of environmental impacts, introduction of compulsory minimum floor space index to land use planning, updating and consistent use of vacant site registers
Avoidance of demolition / Promotion of aggregation of housing units
Marketing campaigns for urban housing, or living in the building stock, reform of the owner-occupied homes premium
Advances in heating structures for existing housing stock and new-build
Marketing campaigns and pilot projects for the use of biomass and district/neighbourhood heating
Increase in insulation retrofitting in the housing stock
Competitions and marketing campaigns promoting living in the housing stock, expansion of federal government and regional state upgrading and modernization programmes
Concrete recycling (for use in building construction)
Broadening of joint federal-regional state programmes for urban renewal (adoption of resource-efficient components)
Proportion of timber construction in new single- and two-family houses
See concrete recycling
Proportion of new-build with cellars
See concrete recycling
A range of the measures and mechanisms listed in Table 6.1 have already undergone detailed development and some have now entered their trial phase.18 These are very important for future implementation processes.
Together, the results of the research project and the various ways in which the BASiS-2 material-flow model can be used to analyse complex relationships in the construction and housing sector provide a valuable foundation which can decisively support the ongoing dialogue and the implementation of sustainable construction and housing policy. Experience gained in the course of the dialogue and implementation process in Schleswig-Holstein, which was based on scenario results obtained with the previous version of the material-flow model (BASiS-1), shows this potential very clearly. In Schleswig-Holstein the results for the sustainability scenario in the construction and housing sector19 serve as a basis for a dialogue process being held throughout the regional state20 and embedded in the framework of its general sustainability strategy.
At subject-specific workshops (“Inner-urban development and housing stock”,
“Sustainable space and water heating” and “Conservation of mineral resources”) in discourse with specialist actors from within the regional state, concrete implementation measures were devised (e.g. measures to develop an infrastructure for wood pellets). These form a key foundation for current activities in the regional state in the construction and housing sector. The long-term results of the sustainability scenario provide useful guidance on future short-, medium- and long-term activities in Schleswig-Holstein to promote sustainable construction and housing.
In view of the results achieved in Schleswig-Holstein, an obvious way to proceed with realizing the sustainable construction and housing perspective is to initiate a comparable dialogue process at national level. The aim of this dialogue process will be to consult with key actors and institutions on specific mechanisms and measures, and to prepare their implementation. The special factors that emerge when addressing the national level (e.g. integration of actors from federal government, federal states and municipality levels) must be given due consideration, as must the results of this project, based as they are on the more extensive analysis yielded by
18 Cf. the in-depth study by difu, with detailed information on various instruments discussed (Apel, D.; Böhme, C.; Meyer, U.; Preisler-Holl, L.; Szenarien und Potentiale einer nachhaltig flächensparenden und landschaftsschonenden Siedlungsentwicklung [Scenarios and potentials of housing development which sustainably minimizes land consumption and landscape degradation]. German Institute of Urban Affairs (difu) commissioned by the German Federal Environmental Agency. Berlin 2001) and the recent publication
“Nachhaltige Entwicklung in Deutschland” [Sustainable development in Germany] (UBA 2002).
19 Buchert, M.; Jenseit, W.; Stahl, H.; Nachhaltiges Bauen und Wohnen in Schleswig-Holstein [Sustainable construction and housing in Schleswig-Holstein], commissioned by the Ministry for Environment, Nature and Forests of the regional state of Schleswig-Holstein (Ed.), Kiel.
20 Buchert, M.; Rheinberger, U.; Umsetzung von nachhaltigem Bauen und Wohnen in Schleswig-Holstein [Implementing sustainable construction and housing in Schleswig-Holstein], commissioned by the Ministry for Environment, Nature and Forests of the regional state of Schleswig-Holstein, Kiel.