The basics of building decarbonization explained
Our know-how section is the go-to resource for insights on the impact of real estate on climate change and the existing technology that solves it. From climate science foundations to industry best practices, our team shares their knowledge and expertise to help you navigate through the topic.
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Insights and know-how you might be interested in:
Climate
Get to know all the basics about climate change, from the Paris Agreement to carbon budgets and embodied emissions. Fundamentals that should be part of general knowledge – not only for sustainability professionals but also non-professionals. Furthermore, widely used reporting frameworks as well as climate metrics are explained.
Buildings
Get to know everything about energy renovations and how to build in a climate-compatible way. Renovation measures such as different heating systems, energy efficiency measures on the building envelope and solar systems are explained including their pros and cons. Diverse aspects of construction and their climate impacts are outlined, from concrete to sufficiency.
Basics
Biogenic carbon
Climate crisis
The climate crisis refers to the ecological and social crisis caused (or predicted) by climate change. The term climate crisis is increasingly being used instead of climate change or global warming to illustrate the scale and urgency of the problem.
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Climate risks
In the context of climate change, risks can arise from both the potential impacts of climate change and human responses to climate change. A distinction is made between two categories of climate risks:
– Transition risks arise from human responses and efforts to cope with climate change, such as: new regulations, changing investor and tenant preferences or new technological developments. In the case of real estate, there is a risk that a building will become a so-called stranded assets, i.e. that there will be a loss of value – e.g. because the building does not meet future standards and regulations and/or because a CO2 tax will result in additional costs in the future. For the assessment of transition risks, the two metrics ITR and CVaR (Carbon Value at Risk) are often used for real estate.
– Physical risks arise from extreme weather events or changing climatic conditions. Physical risks for real estate are e.g. floods, which can lead to major property damage, or heat waves, which lead to overheating in buildings and thus health risks.
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– Transition risks arise from human responses and efforts to cope with climate change, such as: new regulations, changing investor and tenant preferences or new technological developments. In the case of real estate, there is a risk that a building will become a so-called stranded assets, i.e. that there will be a loss of value – e.g. because the building does not meet future standards and regulations and/or because a CO2 tax will result in additional costs in the future. For the assessment of transition risks, the two metrics ITR and CVaR (Carbon Value at Risk) are often used for real estate.
– Physical risks arise from extreme weather events or changing climatic conditions. Physical risks for real estate are e.g. floods, which can lead to major property damage, or heat waves, which lead to overheating in buildings and thus health risks.
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CO2
Carbon dioxide (CO2) is a naturally occurring gas, but also a by-product of fossil fuel combustion, biomass combustion, changes in land use and industrial processes (e.g. cement clinker production). CO2 is responsible for a large part of the human-made greenhouse effect and is thus the most important anthropogenic greenhouse gas in the atmosphere.
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CO2 in the earth’s atmosphere
Atmospheric CO2 describes the total amount of CO2 in the atmosphere, including natural and human-made emissions. Over the past 800’000 years, CO2 concentrations have risen above 300 ppm (part per million, equivalent to one millionth) – until industrialization. Since then, the CO2 concentration has risen rapidly and currently stands at 422 ppm.
Atmospheric CO2 influences the climate through the greenhouse effect and leads to acidification of the ocean due to its solubility.
Graphics: CO2 concentration over the last 800,000 years (NASA)
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Atmospheric CO2 influences the climate through the greenhouse effect and leads to acidification of the ocean due to its solubility.
Graphics: CO2 concentration over the last 800,000 years (NASA)
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CO2 equivalents
The CO2 equivalent describes the global warming potential of a gas, i.e. its relative contribution to global warming compared to CO2. Because different greenhouse gases have different effects on the climate: nitrous oxide is e.g. 265 times and methane 28 times more potent than CO2. CO2 equivalents thus enable comparison between different greenhouse gases. The global warming potentials of the most important greenhouse gases are listed in the GHG Protocol.
Very often when talking about CO2 emissions, the CO2 equivalents are meant.
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Very often when talking about CO2 emissions, the CO2 equivalents are meant.
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CO2 budget
The concept of a carbon/emissions budget is based on an almost linear relationship between cumulative CO2 emissions and temperature rise. It therefore describes the maximum amount of CO2 the world can emit in order not to exceed a certain amount of global warming. In its 6th Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) states a global CO2 budget (from 2020) of 400 gigatons of CO2 if global warming is to be limited to 1.5°C with a probability of 67%.
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Global warming
Global warming describes the increase in the average temperature of the near-Earth atmosphere and oceans caused by climate change since the beginning of industrialization around 1750. According to the Intergovernmental Panel on Climate Change (IPCC), the global average temperature has already increased by 1.1°C.
Global warming has far-reaching and sometimes irreversible consequences for humans and the environment, such as rising sea levels, stronger and more frequent weather extremes and the loss of biodiversity. Switzerland is particularly hard hit: the average temperature here has already increased by 2°C. The other effects of climate change on Switzerland are described in the Swiss Climate Scenarios CH2018.
Graphics: “Show me your stripes” project by the University of Reading
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Global warming has far-reaching and sometimes irreversible consequences for humans and the environment, such as rising sea levels, stronger and more frequent weather extremes and the loss of biodiversity. Switzerland is particularly hard hit: the average temperature here has already increased by 2°C. The other effects of climate change on Switzerland are described in the Swiss Climate Scenarios CH2018.
Graphics: “Show me your stripes” project by the University of Reading
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Embodied emissions
Embodied emissions from buildings are greenhouse gas emissions generated during the extraction, manufacture, transport, installation, maintenance and disposal of building materials and building technology. They occur not only in new buildings (where they often account for more than half of all emissions over the entire life cycle of buildings) but also in any renovation.
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Climate change
Climate change describes the long-term change in climate, i.e. temperatures and weather patterns. These changes may be of natural origin, but since industrialization around 1750, human activities, especially the burning of fossil fuels, have been the main cause of climate change and associated global warming.
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Negative emissions
Negative CO2 emissions are when CO2 is removed from the atmosphere and stored long-term (also called binding back of emissions). There are various negative emission technologies based either on biological (e.g. reforestation) or technical approaches (e.g. mechanical CO2 air filtration and storage (DACCS)). More information on negative emission technologies is available here.
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Greenhouse gases (GHG)
Greenhouse gases are gases that contribute to the greenhouse effect in the atmosphere. They absorb part of the thermal radiation emitted by the ground, which would otherwise escape into space and emit the absorbed energy back to the earth’s surface as thermal radiation. These gases thus influence the earth’s energy balance and have an effect on the climate. The most important natural greenhouse gas is water vapor. However, this is not directly influenced by humans. The most important anthropogenic greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and hydrofluorocarbons (CFCs). The current increase in the concentration of these greenhouse gases caused by human activities amplifies the natural greenhouse effect and leads to global warming. According to the International Energy Agency (IEA), buildings are responsible for 37% of all greenhouse gas emissions worldwide, with operations accounting for 27% and embodied emissions for 10%.
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CO2 footprint
The sum of all greenhouse gas emissions from a given product, installation or activity over its entire life cycle. For buildings, the CO2 footprint is often reported on an annual basis and therefore only takes operational emissions into account.
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Net zero
Net-zero greenhouse gas emissions means that all greenhouse gas emissions generated by an activity are offset by natural or technical sinks, meaning that the activity no longer releases additional greenhouse gases into the atmosphere.
According to the 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), net-zero greenhouse gas emissions must be achieved in order to stop global warming. However, the rise in temperature, i.e. the extent of global warming, does not depend on when net zero is reached, but rather on the cumulative emissions that are released by then. The CO2 reduction path to net zero is therefore crucial.
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According to the 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), net-zero greenhouse gas emissions must be achieved in order to stop global warming. However, the rise in temperature, i.e. the extent of global warming, does not depend on when net zero is reached, but rather on the cumulative emissions that are released by then. The CO2 reduction path to net zero is therefore crucial.
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Paris Agreement
The Paris Agreement is an international treaty of the United Nations Convention on Climate Change (UNFCCC). It was adopted by 195 Parties at the UN Climate Change Conference in Paris (COP 21) on 12 December 2015 and entered into force on 4 November 2016.
The Paris Agreement aims to limit average global warming to well below 2°C compared to pre-industrial times, aiming for a maximum temperature increase of 1.5°C. In addition, the agreement obliges all states to submit and explain a nationally defined reduction target at international level every five years.
The Paris Agreement is a milestone in the multilateral climate change process, as for the first time a binding agreement commits all nations to make ambitious efforts to combat climate change and adapt to its effects.
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The Paris Agreement aims to limit average global warming to well below 2°C compared to pre-industrial times, aiming for a maximum temperature increase of 1.5°C. In addition, the agreement obliges all states to submit and explain a nationally defined reduction target at international level every five years.
The Paris Agreement is a milestone in the multilateral climate change process, as for the first time a binding agreement commits all nations to make ambitious efforts to combat climate change and adapt to its effects.
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United Nations Convention on Climate Change (UNFCCC)
The United Nations Framework Convention on Climate Change (UNFCCC) is the establishment of the United Nations with the aim of slowing global warming and mitigating the consequences of climate change. The agreement has near-universal membership (197 parties) and is the parent contract of the 2015 Paris Agreement.
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Intergovernmental Panel on Climate Change (IPCC)
The Intergovernmental Panel on Climate Change (IPCC) was founded in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to provide policymakers with the most accurate science on climate change. The IPCC’s Assessment Report (AR) and Special Report (SR) are the most well-founded and balanced accounts of the current state of climate research.
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Scope 1 emissions
According to the GHG Protocol, Scope 1 emissions are direct greenhouse gas emissions, i.e. greenhouse gas emissions occurring locally. In a building, they are usually caused by the combustion of oil or gas.
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Scope 2 emissions
According to the GHG Protocol, Scope 2 emissions are indirect greenhouse gas emissions from the consumption of purchased energy such as electricity or district heating.
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Scope 3 emissions
According to the GHG Protocol, Scope 3 emissions are all other indirect greenhouse gas emissions that occur in the upstream and downstream of an organization. For a building, these include e.g. transport and distribution of gas and embodied emissions of purchased products or materials.
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Reporting
CDP
The Carbon Disclosure Project (CDP) is a non-profit organization that annually evaluates companies on their commitment to climate change, water use and deforestation using standardized questionnaires. The questionnaires are aligned with the TCFD recommendations, assessing the following sub-areas:
- D: Disclosure (completeness of disclosure)
- C: Awareness (of environmental risks)
- B: Management (of environmental risks)
- A: Leadership (in the environmental sector)
The answers are summarized into an overall score, the CDP rating, from A to D–. This CDP rating is a valuable benchmark for objectively evaluating and comparing companies and is therefore often published.
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- D: Disclosure (completeness of disclosure)
- C: Awareness (of environmental risks)
- B: Management (of environmental risks)
- A: Leadership (in the environmental sector)
The answers are summarized into an overall score, the CDP rating, from A to D–. This CDP rating is a valuable benchmark for objectively evaluating and comparing companies and is therefore often published.
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GFANZ
The Glasgow Financial Alliance for Net-Zero (GFANZ) is a global coalition of financial institutions committed to a net-zero target. GFANZ members include more than 500 companies from over 45 different countries.
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GRESB
The Global Real Estate Sustainability Benchmark (GRESB) is a global standard for assessing and benchmarking the ESG performance of real estate portfolios and assets. GRESB is based on a survey that covers a range of sustainability issues, including energy and water consumption, greenhouse gas emissions, waste management, building certifications, social and community impacts, governance and management practices, and more.
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CRREM
The Carbon Risk Real Estate Monitor (CRREM) is a non-profit initiative of several scientific institutions, which was launched by the EU Commission. CRREM developed a comprehensive and science-based methodology for assessing the transition risks of real estate – in particular the risk of Stranded Assets. In this context, the CRREM pathways were developed: CO2 reduction pathways for different countries (including Switzerland) and building types that are aligned with a global warming of 1.5°C. These decarbonization pathways are used to benchmark real estate assets and portfolios.
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CVaR
The Carbon Value at Risk (CVaR) is a forward-looking risk indicator developed by CRREM. The CVaR is a metric that quantifies the potential financial losses that could result from a given level of carbon emissions in a real estate portfolio or asset. It is based on the idea of “value at risk” (VaR), which is a widely used risk management tool in finance that measures the potential losses of a portfolio at a given level of confidence over a given time horizon. The CVaR takes into account the potential future costs associated with carbon emissions, such as the cost of carbon taxes, regulation, and physical impacts of climate change, such as increased insurance premiums or property damage. It allows investors to assess the potential financial impact of carbon emissions on their portfolio and to identify high-risk assets or sectors.
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PACTA
The Paris Agreement Capital Transition Assessment (PACTA) is an open-source methodology or tool for standardized climate tests of financial portfolios to analyze their alignment with the Paris Agreement. With the PACTA model, free and internationally coordinated climate tests are carried out regularly, whereby real estate and mortgage portfolios can also be submitted and analyzed.
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SBTi
The Science Based Targets Initiative (SBTi) is an initiative of various international organizations (including WWF and CDP) with the aim of mobilizing the private sector for climate action and decarbonization. The Science Based Targets show companies and financial institutions to what extent and how fast they need to reduce their greenhouse gas emissions in order to limit global warming to 1.5°C in line with the Paris Agreement.
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Swiss Climate Scores
The Swiss Climate Scores were introduced by the Federal Council in summer 2022 and comprise 6 indicators that assess the climate compatibility of financial assets:
Actual state:
- Greenhouse gas emissions (intensity or footprint)
- Exposure to fossil fuels
Transition to net zero:
- Global warming potential / ITR
- Verified Commitments to Net-Zero
- Management at Net-Zero (intermediate targets and decarbonisation path)
- Credible climate dialogue
The Swiss Climate Scores are voluntary. However, the Federal Council recommends that all Swiss financial market players apply them and thus create transparency and comparability.
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Actual state:
- Greenhouse gas emissions (intensity or footprint)
- Exposure to fossil fuels
Transition to net zero:
- Global warming potential / ITR
- Verified Commitments to Net-Zero
- Management at Net-Zero (intermediate targets and decarbonisation path)
- Credible climate dialogue
The Swiss Climate Scores are voluntary. However, the Federal Council recommends that all Swiss financial market players apply them and thus create transparency and comparability.
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TCFD
The Task Force on Climate-related Financial Disclosures (TCFD) is an initiative launched in 2015 by the Financial Stability Board (FSB) with the mandate to develop recommendations for corporate disclosure and reporting of climate risks. The TCFD recommendations have become the de facto standard for climate reporting and are used by regulators worldwide.
In addition to recommendations on governance, strategy and risk management, the TCFD recommendations also contain recommendations on climate metrics and targets. Recommended metrics include:
- Absolute emissions and CO2 intensity
- Proportion of assets or financing activities exposed to climate risks
- Future-oriented temperature alignment, e.g. with ITR
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In addition to recommendations on governance, strategy and risk management, the TCFD recommendations also contain recommendations on climate metrics and targets. Recommended metrics include:
- Absolute emissions and CO2 intensity
- Proportion of assets or financing activities exposed to climate risks
- Future-oriented temperature alignment, e.g. with ITR
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REIDA
The Real Estate Investment Data Association (REIDA) is a non-profit organization with the goal to continuously improve the data situation in the Swiss real estate market. REIDA recently launched a CO2 benchmarking framework for real estate portfolios, which is based on and aligned with the minimum requirements of AMAS. The REIDA CO2 benchmark includes the same KPIs as defined by AMAS but precisely defines the methodological foundations for the calculation. This enables the uniform calculation and thus the comparison of these parameters. The REIDA CO2 benchmark also shows how to deal with uncertainties in measurement and balancing.
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AMAS
The Asset Management Association Switzerland (AMAS) is the representative association of the Swiss asset management industry. In 2022 AMAS defined environmentally relevant KPIs for real estate funds according to Swiss law.
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SSREI
The Swiss Sustainable Real Estate Index (SSREI) is used to assess the sustainability of the Swiss real estate portfolio. Like the SNBS for construction, SSREI AG is based on the SIA standard 112/1 "Sustainable Construction - Building Construction".
Developed for use on existing properties, the 36 assessment indicators allow a comprehensive assessment of the condition of a property in the areas of society, economy and environment.
The resulting assessment results can be used to derive portfolio- and property-specific sustainability strategies and define specific measures. The ratings also serve as a meaningful basis for transparent and comparable sustainability reporting.
The clearly defined and publicly accessible evaluation process is certified by the SQS - Swiss Association for Quality and Management Systems.
The Swiss Sustainable Real Estate Index is also recognized internationally by GRESB (Global Real Estate Sustainability Benchmark).
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Developed for use on existing properties, the 36 assessment indicators allow a comprehensive assessment of the condition of a property in the areas of society, economy and environment.
The resulting assessment results can be used to derive portfolio- and property-specific sustainability strategies and define specific measures. The ratings also serve as a meaningful basis for transparent and comparable sustainability reporting.
The clearly defined and publicly accessible evaluation process is certified by the SQS - Swiss Association for Quality and Management Systems.
The Swiss Sustainable Real Estate Index is also recognized internationally by GRESB (Global Real Estate Sustainability Benchmark).
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GHG Accounting
Switzerland’s greenhouse gas inventory
The national greenhouse gas inventory contains comprehensive statistics on emissions according to the requirements of the UN Climate Convention. Additionally, the greenhouse gas inventory defines the emission factors which are to be used for national and cantonal reporting, i.e. they are used for GEAK and to calculate the CO2 tax. According to the inventory, only direct CO2 emissions, i.e. emissions that result from on-site combustion of oil/gas, are attributed to the building (Scope 1).
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GHG Protocol
The Greenhouse Gas Protocol (GHG Protocol) is a standard (or series of standards) for accounting of greenhouse gas emissions, which is coordinated by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD). The GHG Protocol defines the global warming potential of the most important greenhouse gases and classifies Scope 1, 2 and 3 emissions. In contrast to the SIA/KBOB framework, the GHG Protocol allows the distinction between direct (Scope 1) and indirect (Scope 2 and 3) emissions and is therefore used by numerous reporting standards such as AMAS, REIDA, PCAF, CRREM, TCFD, SBTi, etc.
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SIA/KBOB
Life cycle and energy assessments according to SIA (SIA 380 and SIA 2040 / SIA 2032) are based on the data source Ökobilanzdaten im Baubereich (current version: 2009-1:2022), which is jointly published by KBOB (Vereinigung der öffentlichen Bauherren der Schweiz), the ecobau association and IPB (Interessensgemeinschaft privater professioneller Bauherren). The emission factors consider the entire life cycle and therefore include, in addition to the direct emissions from energy use, the emissions from upstream and downstream processes. A breakdown of direct emissions and LCA share of the emission factors is missing which is why the SIA/KBOB framework cannot be used for reporting frameworks that are based on the GHG Protocol (such as AMAS, REIDA, PCAF, CRREM, etc.).
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Temperature Alignment
Temperature alignment describes the use of future-oriented climate metrics to ensure the compliance of an asset (e.g. a building or building module) with a specific climate target (e.g. the 1.5°C climate target). A widely used metric is the Global Warming Potential – also known as the Implied Temperature Rise (ITR) – which shows in an intuitively understandable way the extent of global warming which an asset causes.
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Metrics
GEAK
The Building Energy Performance Certificate of the Cantons (GEAK) is the official energy label of the Swiss cantons and by far the most frequently used building label in Switzerland. Due to its widespread use and uniform calculation methodology, the GEAK is suitable for rating and comparing buildings. It rates the following three aspects with seven different classes (from A = very good to G = very bad):
- GEAK Effizienz Gebäudehülle: Efficiency of the building envelope (i.e. the heating demand)
- GEAK Effizienz Gesamtenergie: Overall energy efficiency (i.e. the final energy demand, whereby the different energy sources are weighted with national weighting factors)
- GEAK Direkte CO2-Emissionen: Direct CO2 emissions (according to Switzerland’s greenhouse gas inventory)
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- GEAK Effizienz Gebäudehülle: Efficiency of the building envelope (i.e. the heating demand)
- GEAK Effizienz Gesamtenergie: Overall energy efficiency (i.e. the final energy demand, whereby the different energy sources are weighted with national weighting factors)
- GEAK Direkte CO2-Emissionen: Direct CO2 emissions (according to Switzerland’s greenhouse gas inventory)
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Minergie
Minergie is a Swiss building standard for new and modernized buildings which focuses on comfort, operational energy efficiency and value retention and has high requirements in terms of building envelope insulation and systematic air renewal (through mechanical ventilation). In addition to the normal Minergie standard there are the following standards:
Minergie-P meets the requirements of lowest-energy buildings.
- Minergie-A focuses on independence through self-production.
- Minergie ECO additionally takes health, building ecology and embodied energy and emissions into account.
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Minergie-P meets the requirements of lowest-energy buildings.
- Minergie-A focuses on independence through self-production.
- Minergie ECO additionally takes health, building ecology and embodied energy and emissions into account.
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Energiekennzahl (EKZ)
The Energiekennzahl (EKZ) describes the total energy demand or consumption of a building during one year in relation to the energy reference area. The calculation methodology is defined in the Swiss standard SIA 380:2021. The EKZ takes into account the energy demand for heating, cooling, ventilation, hot water, lighting, and other electrical devices and is expressed in kilowatt-hours per square meter per year (kWh/m²a).
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Treibhausgasemissions-Kennzahl / CO2 footprint (operational emissions)
The Treibhausgasemissions-Kennzahl (also known as CO2 footprint) describes the total greenhouse gas emissions caused by the energy consumption of a building during one year in relation to the energy reference area. These operational GHG emissions include both direct emissions (burning of oil or gas) and indirect emissions (purchased electricity or district heating). The calculation methodology is defined in the Swiss standard SIA 380:2021.
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Erstellungsemissionen (embodied emissions)
Embodied emissions are greenhouse gas emissions generated during the extraction, manufacture, transport, installation, maintenance and disposal of building materials and technology. The calculation methodology is defined in the Swiss standard SIA 2032:2020. Consideration of embodied emissions is particularly important for new buildings, where embodied emissions account for the vast majority of life-cycle emissions.
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AMAS (building specific)
AMAS defined the following energy and climate KPIs for real estate portfolios:
- Coverage ratio in %: Proportion of properties in the portfolio for which data is available and disclosed
- Energy mix: Share of fossil energy sources in %
- Energy consumption* in MWh per year
- Energy intensity* in kWh per year and m2 energy reference area
- CO2e emissions* (GHG emissions) in tons of CO2 equivalents per year: accounting based on GHG Protocol, considers Scope 1 and 2 emissions with Swiss average emission factors for electricity and district heat (location-based approach)
- CO2e emission intensity* (GHG emission intensity) in kg CO2 equivalents per year and m2 energy reference area: accounting based on GHG Protocol, considers Scope 1 and 2 emissions with Swiss average emission factors for electricity and district heat (location-based approach)
*This KPI is also required by REIDA.
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- Coverage ratio in %: Proportion of properties in the portfolio for which data is available and disclosed
- Energy mix: Share of fossil energy sources in %
- Energy consumption* in MWh per year
- Energy intensity* in kWh per year and m2 energy reference area
- CO2e emissions* (GHG emissions) in tons of CO2 equivalents per year: accounting based on GHG Protocol, considers Scope 1 and 2 emissions with Swiss average emission factors for electricity and district heat (location-based approach)
- CO2e emission intensity* (GHG emission intensity) in kg CO2 equivalents per year and m2 energy reference area: accounting based on GHG Protocol, considers Scope 1 and 2 emissions with Swiss average emission factors for electricity and district heat (location-based approach)
*This KPI is also required by REIDA.
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ITR
The Implied Temperature Rise (ITR) – also called global warming potential – is an intuitive and future-oriented climate metric that indicates the climate impact of an asset (e.g. a building) based on degrees Celsius (°C) of global warming. The ITR answers the question: How many degrees would the climate warm up if the entire world had the same emission intensity as the building under consideration? Compared to other climate metrics, the ITR is intuitively understandable and allows to compare different asset classes.
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Heating systems
Heating systems (Intro)
Heating systems produce heat for heating and hot water, through converting energy sources such as oil, gas, wood, district heating, electricity or free environmental heat into useful heat. Depending on the type of energy source, heat generation produces different amounts of CO2 emissions: the combustion of fuel (oil and gas) causes a lot of emissions, while environmental heat from the ground, ambient air or groundwater is CO2 neutral. The CO2 intensity of district heating and electricity depends on the production, i.e. whether the heat or electricity is generated with renewable energy sources.
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Geothermal heat pump
Heat is extracted from the ground via geothermal probes (a frost-proof liquid circulates through the probes and heats up), which is then brought to a higher temperature level to produce heating water or hot water with the help of a heat pump. Since the temperature of the ground is more constant and in winter also higher than the outdoor air temperature, geothermal heat pumps are more efficient than air-source heat pumps. In combination with floor heating, geothermal heat pumps allow passive cooling of the building in summer (Free Cooling). The installation at a single-family home takes about two weeks.
Advantages:
- No fossil fuels
- Very efficient and cost-effective operation
- Geothermal probes are not visible and audible
- Geothermal probes have a very long service life of over 50 years and therefore lead to an increase in the value of the property
- Cost-effective and ecological cooling function
Disadvantages:
- High investment costs
- Not feasible everywhere
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Advantages:
- No fossil fuels
- Very efficient and cost-effective operation
- Geothermal probes are not visible and audible
- Geothermal probes have a very long service life of over 50 years and therefore lead to an increase in the value of the property
- Cost-effective and ecological cooling function
Disadvantages:
- High investment costs
- Not feasible everywhere
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Air-source heat pump
The outside air is sucked in with a fan in order to extract heat from it, which is then brought to a higher temperature level to produce heating water or hot water. Modern air-source heat pumps can still produce sufficient heat even in very cold winter air. The installation at a single-family home takes about one week.
Advantages:
- No fossil fuels
- Efficient and cost-effective operation
- Cooling function can be integrated
Disadvantages:
- High investment costs
- Causes noise and is visible when placed outdoors
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Advantages:
- No fossil fuels
- Efficient and cost-effective operation
- Cooling function can be integrated
Disadvantages:
- High investment costs
- Causes noise and is visible when placed outdoors
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Groundwater heat pump
Heat is extracted from the groundwater via an extraction well and is then brought to a higher temperature level with the help of a heat pump to produce heating or hot water. Since the temperature of the groundwater is more constant and also higher in winter than the outside air temperature, groundwater heat pumps are more efficient than air-source heat pumps. Due to the more complex construction, groundwater heat pumps are particularly suitable for larger properties.
Advantages:
- No fossil fuels
- Very efficient and cost-effective operation
Disadvantages:
- High investment costs
- Long planning and approval process
- Not feasible everywhere
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Advantages:
- No fossil fuels
- Very efficient and cost-effective operation
Disadvantages:
- High investment costs
- Long planning and approval process
- Not feasible everywhere
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Pellet heating
A pellet heating system is a wood combustion plant that burns pellets to generate heat for heating or hot water. The pellets are temporarily stored in a large storage room or silo until they are burned.
Advantages:
- No fossil fuels
Disadvantages:
- Large space requirement for storage space or silo
- Costly maintenance
- Particulate matter (PM) emissions
- High operating costs
- “Waste” of high-quality energy (exergy), which could be used to produce electricity
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Advantages:
- No fossil fuels
Disadvantages:
- Large space requirement for storage space or silo
- Costly maintenance
- Particulate matter (PM) emissions
- High operating costs
- “Waste” of high-quality energy (exergy), which could be used to produce electricity
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District heating
District heat is generated in a central plant – for example, a waste incineration plant, sewage treatment plant or a combined heat and power plant – and is supplied to customers via a pipeline network to produce heating or hot water. For this purpose, a transfer station is installed in the house.
Advantages:
- No fossil fuels (depending on the heat source!)
- Low investment costs
Disadvantages:
- Often high operating costs
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Advantages:
- No fossil fuels (depending on the heat source!)
- Low investment costs
Disadvantages:
- Often high operating costs
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Oil heating
The combustion of oil is used to generate heating or hot water. The oil is stored in an oil tank until combustion.
Advantages:
- Low investment costs
Disadvantages:
- Fossil fuel / not climate-friendly
- High operating costs
- Dependent on foreign energy imports
- High space requirement due to oil tank
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Advantages:
- Low investment costs
Disadvantages:
- Fossil fuel / not climate-friendly
- High operating costs
- Dependent on foreign energy imports
- High space requirement due to oil tank
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Gas heating
The combustion of gas (e.g. natural gas or biogas) is used to generate heating or hot water. For this, the property must be connected to a gas network.
Advantages:
- Low investment costs
Disadvantages:
- Fossil fuel / not climate-friendly
- High operating costs
- Dependent on foreign energy imports
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Advantages:
- Low investment costs
Disadvantages:
- Fossil fuel / not climate-friendly
- High operating costs
- Dependent on foreign energy imports
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Envelope efficiency
Roof renovation incl. insulation
For a roof renovation there are different insulation methods: the above-rafter insulation, between-rafter insulation and the under-rafter insulation (for a pitched roof) and the flat roof insulation. Between- and under-rafter insulation can be installed from the inside, i.e. without removing the roof covering. In a complete renovation of a pitched roof, above-rafter and between-rafter insulation is usually installed in addition to the renewal of the roof covering.
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Attic insulation
If the attic is not heated and there is no plan to convert it into living space, attic insulation (also called top floor ceiling insulation) is feasible. Either insulation mats can be laid or an insulating material can be blown in. By using overlying plates, the attic remains accessible. An attic insulation is significantly more cost-effective and less complex than a complete roof renovation with above-rafter and between-rafter insulation.
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Facade insulation
There are different variants for facade insulation: exterior, interior and core insulation. In the case of buildings that are not listed as protected objects, exterior insulation is usually applied, whereby there are the following two methods: the compact facade (also called external thermal insulation composite system or ETICS) and the ventilated curtain facade. With a compact facade, the thermal insulation boards are glued directly to the existing façade from the outside. Then a reinforcement layer and finally an external plaster are applied to it. In the case of the ventilated curtain facade, the insulation panels are also glued directly to the existing facade, but the new facade covering is erected with a scaffolding system with some distance to the thermal insulation. This scaffolding (also called substructure) is attached to the old facade and supports the new facade covering. A ventilated curtain facade keeps weather-related influences away from the insulation and ensures good air circulation and moisture removal. For this reason, a ventilated curtain facade has a significantly longer service life than a compact facade. Further advantages are the design freedom in the facade covering and the fact that renewable insulation materials such as wood fibre can also be used (which leads to lower embodied emissions). The only disadvantage compared to the compact facade is the higher costs.
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Cellar ceiling insulation
If the cellar is not heated, cellar ceiling insulation is feasible. With this cost-effective renovation measure, insulation boards are attached to the cellar ceiling from below (either glued or doweled). Mineral insulation materials such as rock wool are usually used for this purpose.
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Window replacement
Older, poorly insulated windows can be replaced by modern, energy-efficient windows. In particular, triple-glazed windows with insulating glazing have very good thermal insulation properties. Window frames are offered in plastic, aluminum, wood and combinations such as wood-aluminum. A wood-aluminium frame has relatively few embodied emissions and is also very weather-resistant and therefore durable. Compared to a plastic frame, however, it is slightly more expensive.
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Solar systems
Photovoltaic system
Photovoltaic systems (PV systems) consist of solar cells and can convert part of the solar radiation into electrical energy. This electricity can either be used directly at the point of generation, stored in a battery storage system or fed into the grid of the local utility provider. The profitability of a PV system depends strongly on the design and size of the system, the self-consumption (which is increased, for example, with a heat pump or an electric car) and the feed-in tariff for electricity fed into the grid. There are different forms of PV systems: on-roof systems, in-roof systems, solar tiles and solar facades. On-roof systems are installed on the roof by means of a mounting system, while in-roof systems, solar tiles and solar facades replace the weatherproof building envelope of the roof or facade. On-roof systems are easy to install and relatively inexpensive, while in-roof systems and solar tiles have aesthetic advantages and are particularly suitable if the roof is being comprehensively renovated anyway.
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Thermal solar collectors
Thermal solar collectors can absorb the sun’s rays and convert them into heat. This heat is stored in heat storage tanks and can then be used to heat the hot water, to support the heating or to regenerate the geothermal probes. In contrast to the electricity feed-in option with a PV system, the excess heat cannot be used or sold with thermal collectors. Another disadvantage compared to the PV system is the more complex maintenance. In addition, it often makes more economic sense to generate hot water by means of a heat pump and PV system than thermal solar collectors directly.
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Construction
Concrete
The production of concrete or cement, the most important component of concrete, produces large amounts of CO2 emissions. On the one hand, cement production is very energy-intensive and therefore often CO2-intensive (if fossil fuels are used). However, most of CO2 emissions are caused by a chemical reaction during the combustion process (geogenic CO2 dissolves from the limestone). Overall, cement production is responsible for around 8% of global greenhouse gas emissions – about four times as much as the total global aviation industry. However, reinforced concrete is indispensable for certain constructions, e.g. in the underground. In order to minimize embodied emissions in buildings, underground construction should therefore be avoided as far as possible. In addition, the choice of concrete also plays a role, as for some types embodied CO2 emissions are up to 40% lower.
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Biogenic construction materials
Biogenic construction materials are based on renewable raw materials such as wood, sheep's wool, straw or hemp and usually have low embodied emissions. The decisive factor for embodied emissions is that the biogenic material is available as regionally as possible, is grown sustainably and is not processed too much (with as little binder as possible). Many biogenic materials such as wood, straw or hemp also bind CO2 (biogenic carbon), which was removed from the atmosphere by photosynthesis during plant growth. Most Life Cycle Assessments do not consider the (interim) stored carbon as negative emissions, for the following reasons:
- It would have to be ensured or guaranteed that the carbon does not re-enter the atmosphere at the end of the component’s life.
- The sink performance only takes place when the extracted raw material grows back and is therefore an ongoing process. As a result, the negative emissions (if at all) will only occur in the future and may therefore only be offset then. In addition, it would have to be ensured or guaranteed that the renewable raw material reaches the same level as the extracted raw material.
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- It would have to be ensured or guaranteed that the carbon does not re-enter the atmosphere at the end of the component’s life.
- The sink performance only takes place when the extracted raw material grows back and is therefore an ongoing process. As a result, the negative emissions (if at all) will only occur in the future and may therefore only be offset then. In addition, it would have to be ensured or guaranteed that the renewable raw material reaches the same level as the extracted raw material.
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Insulation
Insulation reduces the heating demand and thus also the operational greenhouse gas emissions – but by how much depends on the energy source used. However, insulation always causes embodied emissions. How high these are depends on the insulation material, whereby biogenic materials such as wood fibres perform much better than plastic-based insulation such as EPS (expanded polystyrene), which are made from petroleum.
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Windows
Since the production process of glass is very energy- and emission-intensive, many embodied emissions are stuck in one window. There are even more embodied emissions in a glass facade than in a concrete wall. For this reason, the window area should be kept as low as possible and only as much glass as necessary should be installed. In order to minimize embodied emissions from the window itself, window frames made of wood or a wood/aluminum combination should be chosen instead of plastic.
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Floor heating
Surface heat dissipation such as floor heating can be optimally combined with heat pumps and has the following two advantages over radiators: On the one hand, floor heating requires relatively low heating supply temperatures of around 35°C (compared to 50°C for radiators), which leads to a more efficient heat pump operation (lower electricity consumption). On the other hand, surface heat dissipation such as floor heating can also be used for cooling with a heat pump. With radiators, often only minimum cooling power can be achieved. Despite these advantages of floor heating, radiators can also be easily combined with heat pumps.
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Building floor plan
In order to minimize embodied emissions, the building floor plan should be as efficient as possible, i.e. the ratio of usable area to total floor area should be optimized. In addition, the sanitary units should be placed on top of each other to keep the sanitary pipes as short as possible.
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Compactness
Compact construction means minimizing the ratio of exterior sections to floor space. The more compact the construction, the fewer embodied emissions are generated during construction. In addition, a compact shape also has a positive effect on the heating demand and thus on operational emissions.
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Cooling
Switzerland is particularly affected by climate change: while the global average temperature has risen by 1.2°C so far, the average temperature in Switzerland has already increased by 2°C since 1864. Especially in cities, the heat stress is particularly high. Sealed surfaces, the lack of green areas and the limited wind circulation due to dense development as well as the waste heat from industry and traffic contribute to the heat island effect, which increases heating during the day and significantly reduces cooling at night.
With increasing heating, cooling is becoming necessary for more and more buildings. According to Swiss standards, cooling is necessary for existing buildings if the room temperature is above 26.5°C for more than 400 hours per year (whereby the verification must be carried out with a dynamic simulation program). This is where another advantage of heat pumps comes into play: they can be used for both heating and cooling. The resulting electricity demand can be generated by photovoltaic systems as cooling and thus also the electricity demand are highest in summer at noon – and this is exactly when photovoltaic systems generate the most electricity.
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With increasing heating, cooling is becoming necessary for more and more buildings. According to Swiss standards, cooling is necessary for existing buildings if the room temperature is above 26.5°C for more than 400 hours per year (whereby the verification must be carried out with a dynamic simulation program). This is where another advantage of heat pumps comes into play: they can be used for both heating and cooling. The resulting electricity demand can be generated by photovoltaic systems as cooling and thus also the electricity demand are highest in summer at noon – and this is exactly when photovoltaic systems generate the most electricity.
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Longevity
The longer a component can be used, the less frequently it will have to be replaced in the future, which in turn leads to fewer (future) embodied emissions. However, the embodied emissions caused during construction occur in the here and now and cannot be distributed over the lifetime. The conversion to one year (kg CO2/m2EBF/a) allows a comparison with operating emissions, but does not correspond to physical reality: The embodied CO2 is already in the atmosphere and is already climate-effective.
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Masonry
In terms of embodied emissions, a concrete wall performs the worst, followed by the brick wall. Embodied emissions can be reduced if cement or sand-lime bricks are used instead of conventional bricks. However, the most climate-friendly variant is clearly the timber construction.
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Radiators
The myth that radiators cannot be combined with heat pumps due to the high heating supply temperatures is still widespread. However, it is no longer true. Modern heat pumps can generate high temperatures of up to 65°C with acceptable efficiency even on very cold winter days. In addition, with renovation measures on the building envelope (such as basement ceiling insulation), the radiators can be operated with lower temperatures, which increases the efficiency of the heat pump. For this reason, especially in older buildings, measures on the building envelope should always be checked in the event of an imminent heating replacement. Often a combination of measures on the building envelope with a heat pump is the financially and ecologically most attractive solution.
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Sufficiency
In addition to efficiency (reduction of energy losses, e.g. by insulating the building envelope) and consistency (use of renewable energies), sufficiency is the third of the three sustainability strategies. Sufficiency is the limitation or reduction of demand and consumption. In the building sector, this means, for example, reducing the room temperature or space consumption. If the room temperature is reduced by 1°C, the heating demand is reduced by approx. 6% (Schweizer Mittelland). In addition, sustainable construction and living ultimately help little if every person would claim an immensely large living space. In contrast to efficiency and consistency, which can be increased with technical measures, sufficiency is about measures that require behavioral changes in people.
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Underground construction
Underground construction is using very energy- and emission-intensive building materials such as concrete or steel, resulting in high embodied emissions. Therefore, underground construction should be minimized as much as possible. A basement is needed for practically every building – but it should not be built deeper than one floor. Underground car parks should be avoided and it should not be built into the groundwater or the slope.
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Load-bearing structure
The load-bearing structure of a building is responsible for around one third of the embodied greenhouse gases in the construction and therefore, be optimized and made as lean as possible. This means that loads are transferred as easily and directly as possible.
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Circular construction
In circular construction, durable materials are used, which can be well dismantled and reused in the future. The building stock is not regarded as worthless but used as a source of material. With the reuse of components, not only material cycles can be closed and waste avoided but also large amounts of embodied emissions can be saved. In a pioneering project in Winterthur, for example, embodied emissions were reduced by 60% (compared to new components) by reusing components. There are now online platforms such as Madaster, which precisely inventory the materials and products used in a building and thus promote the circular economy.
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