| dc.description.abstract | This report has been commissioned by the Norwegian Directorate for Cultural Heritage with the aim of providing an overall picture of the environmental significance of the reuse of existing buildings. The approach used has involved a systematic assessment and meta-analysis of life cycle assessments performed in connection with the rehabilitation and upgrading of existing buildings. The study has reviewed Norwegian and international publications containing life cycle assessments of existing buildings. The selection of Norwegian case studies was made based on previously completed research projects. Some international case studies were also reviewed, some of which were suggested by the Norwegian Directorate for Cultural Heritage. Data from these sources were used to carry out a high-level meta-analysis, and to provide an overview of results taken from known life cycle assessments of existing buildings. As part of the background to, and discussion included in, this report, major focus has been directed towards the cultural heritage value of existing building stock.
A key factor behind this study is Norway’s target to become a low-emissions society by 2050, which has its foundation in the Paris Agreement and the UN Sustainable Development Goals. In spite of the emergence in many countries of climate-related ambitions and political targets, the volume of global greenhouse gas (GHG) emissions continues to increase. The UN Environment Programme’s ‘Emissions Gap Report 2019’ highlighted the limited realisation of national commitments in the Paris Agreement, and which at current implementation rates will not be sufficient to achieve the goals set out in the agreement. Achievement of the 1.5-degree Celsius global warming target will require greater levels of ambition, combined with the much faster implementation of a wide range of measures during the coming decades. This situation shows just how important it is to be researching how our existing building stock can contribute towards achieving our climate-related political targets for emission reductions. About 80 to 90% of our existing building stock will still be in use in 2050. In Norway, current building upgrade rates are low (at about 1 to 1.4%). The EU Commission has pointed out that 75% of the EU’s current building stock is energy inefficient, and that building upgrades have the potential to provide energy savings and GHG emission reductions of between 5 and 6%. Considering that most of the world’s building stock in 2050 already exists today, the rehabilitation and adaptive reuse of existing buildings will make a decisive contribution to a sustainable future.
The research front indicates that the potential environmental benefits of upgrading existing buildings are great compared with the potential benefits from new-build projects, because the emissions generated during rehabilitation represent only a half of those associated with new builds. Results from Life Cycle Assessment (LCA) studies indicate that GHG reductions in the case of existing buildings are mainly the result of reduced embodied GHG emissions. This means that by conserving existing buildings, and the materials in them, we can avoid the embodied emissions that are inherent in the construction of new buildings. New builds involve not only more waste generation from the demolition of old buildings, but the energy and emissions associated with the production, transport, and installation of new materials, products, and elements, as well as waste generation in the construction process. The Norwegian case studies reveal that GHG emissions linked to the use of materials for the upgrading of existing buildings amount to only a third of those linked to new build projects.
This study demonstrates that, if possible, the environmentally sound upgrading of existing buildings should be favoured in preference to their demolition and replacement by new builds, because reuse is more in harmony with the targets set out in the Paris Agreement and the UN Sustainable Development Goals. In the case of new buildings, results indicate that it takes ten years before the environmental benefits from lower annual emissions from in-use energy consumption offset the negative impacts from the increase in emissions from their construction. Findings in the literature support the idea that rehabilitation is preferable in the 30-year perspective as we approach 2050, because it may take anything from 10 to 80 years before a new building can offset the GHG emissions that are generated during its construction (in year zero). We may conclude from this that, from an environmental perspective, the rehabilitation of existing buildings will be more beneficial to the environment in the short and medium term.
The selection of locally sourced low-carbon materials, combined with the use of renewable energy and the implementation of energy efficiency measures, are the most important ways of reducing emissions, and should be given due consideration during the upgrading of existing buildings. There is wide variation in the energy efficiency potential of the existing building stock, depending on factors such as age, materials use, construction elements, conservation value, and current status of preservation. Requirements related to energy consumption and efficiency measures should be tailored to the type of building in question and its specific circumstances. The case studies presented in this report exhibit large variations in possible GHG emission reductions, which are the result of a number of methodological choices. Naturally enough, the results also vary depending on case-specific factors such as the rehabilitation measures considered. For this reason, we conclude that comprehensive life cycle assessments offer important decision-making tools in our search to identify exactly what constitutes effective rehabilitation measures.
A life cycle approach is key to obtaining more thorough assessments of the sustainability of existing buildings. This study has revealed that few LCAs of existing buildings have been carried out. Moreover, there are major uncertainties linked to the studies that have been performed, largely due to variability and deficiencies inherent in the methods applied. A life cycle assessment is of greater value when it incorporates environmental indicators other than simply GHG emissions, combined with social/societal and economic factors. Such assessments help avoid problem-shifting, and can help ensure that environmentally-friendly measures are not implemented at the expense of other important factors such as cultural and historic conservation considerations.
If life cycle assessments are to be used to support decision-making, the scenarios used to evaluate the various approaches to building rehabilitation or demolition should be as realistic as possible. Basic uncertainties inherent in the scenarios must be discussed to a much greater extent than is currently the case. Assessments that examine only materials use and use-phase energy consumption are insufficient to provide an informed basis for decision making in a scenario involving the choice between the rehabilitation of a building versus demolition and new construction. The assessments should take into account the emissions generated during the construction phase, as well as those related to waste disposal activities linked to both the existing and new building. Inherent uncertainties in the energy calculations must also be highlighted as part of such assessments because they are crucial to the results.
This report draws the following three main conclusions based on the findings from this study:
1) There exists a major unrealised potential in terms of environmental benefits linked to existing building stock. If possible, rehabilitation should be favoured in preference to demolition and the construction of new buildings, in accordance with Norwegian and international climate change targets.
2) When assessing environmentally friendly rehabilitation measures, both cultural and historic conservation considerations should be taken into account.
3) Comprehensive life cycle assessments represent key decision-making support tools, helping to identify the most effective rehabilitation measures.
In conclusion, the following list of recommendations is presented based on the findings and conclusions drawn from this study:
• Ambitions related to building rehabilitation projects must be clearly defined.
• Comprehensive life cycle assessments should be used as decision support tools.
Environmental LCAs should be combined with Life Cycle Costing (LCC) and Social Life Cycle Assessment (SLCA) in order to obtain more holistic and sustainable perspectives on existing buildings.
• All possible rehabilitation measures should be considered when it comes to cultural heritage buildings, provided that these are not implemented at the expense of their conservation value.
• A process of gathering documentation related to best practice should be started.
• Incentives and subsidy schemes for the extensive rehabilitation projects should be evaluated and introduced.
• The UN Sustainable Development Goals should be used as a tool to influence the sustainable development of our building stock. | en_US |
