Editing IPCC:AR6/WGIII/Chapter-9 (section)

== 9.1 Introduction ==

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Total GHG emissions in the building sector reached 12 GtCO 2 -eq in 2019, equivalent to 21% of global GHG emissions that year, of which 57% were indirect CO 2 emissions from offsite generation of electricity and heat, followed by 24% of direct CO 2 emissions produced on-site and 18% from the production of cement and steel used for construction and/or refurbishment of buildings. If only CO 2 emissions would be considered, the share of buildings CO 2 emissions increases to 31% out of global CO 2 emissions. Energy use in residential and non-residential buildings contributed 50% and 32% respectively, while embodied emissions contributed 18% to global building CO 2 emissions. Global final energy demand from buildings reached 128.8 EJ in 2019, equivalent to 31% of global final energy demand. Residential buildings consumed 70% out of global final energy demand from buildings. Electricity demand from buildings was slightly above 43 EJ in 2019, equivalent to more than 18% of global electricity demand. Over the period 1990–2019, global CO 2 emissions from buildings increased by 50%, global final energy demand grew by 38%, with 54% increase in non-residential buildings and 32% increase in residential ones. Among energy carriers, the growth in global final energy demand was strongest for electricity, which increased by 161%.

There is growing scientific evidence about the mitigation potential of the building sector and its contribution to the decarbonisation of global and regional energy systems, and to meeting Paris Agreement goals and Sustainable Development Goals (SDGs) ( [[#IPCC--2018|IPCC, 2018]] ; [[#IEA--2019c|IEA, 2019c]] ; [[#IEA--2019e|IEA 2019e]] ). Mitigation interventions in buildings are heterogeneous in many different aspects, from building components (envelope, structure, materials, etc.) to services (shelter, heating, etc.), to building types (residential and non-residential, sometimes also called commercial and public), to building size, function, and climate zone. There are also variations between developed and developing countries in mitigation interventions to implement, as the former is challenged by the renovation of existing buildings while the latter is challenged by the need to accelerate the construction of new buildings.

This chapter aims at updating the knowledge on the building sector since the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5) (Lucon et al. 2014). Changes since AR5 are reviewed, including: the latest development of building service and components ( [[#9.2|Section 9.2]] ), findings of new building related GHG emission trends ( [[#9.3|Section 9.3]] ), latest technological ( [[#9.4|Section 9.4]] ) and non-technological ( [[#9.5|Section 9.5]] ) options to mitigate building GHG emissions, potential emission reduction from these measures at global and regional level ( [[#9.6|Section 9.6]] ), links to adaptation ( [[#9.7|Section 9.7]] ) and sustainable development ( [[#9.8|Section 9.8]] ), and sectoral barriers and policies ( [[#9.9|Section 9.9]] ).

The chapter introduces the concept of sufficiency, identified in the literature as a mitigation strategy with high potential, and is organised around the Sufficiency, Efficiency, Renewables (SER) framework (Box 9.1).

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=== Box 9.1 | SER (Sufficiency, Efficiency, Renewables) Framework ===

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The SER framework was introduced in the late 1990s by a French NGO ( [[#Negawatt--2017|Negawatt 2017]] ) advocating for a decarbonised energy transition. In 2015, the SER framework was considered in the design of the French energy transition law, and the French energy transition agency (ADEME) is developing its 2050 scenario based on the SER framework.

The three pillars of the SER framework include (i) sufficiency, which tackles the causes of the environmental impacts of human activities by avoiding the demand for energy and materials over the lifecycle of buildings and goods, (ii) efficiency, which tackles the symptoms of the environmental impacts of human activities by improving energy and material intensities, and (iii) the renewables pillar, which tackles the consequences of the environmental impacts of human activities by reducing the carbon intensity of energy supply (Box 9.1, Figure 1). The SER framework introduces a hierarchical layering, sufficiency first followed by efficiency and renewable, which reduces the cost of constructing and using buildings without reducing the level of comfort of the occupant.

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[[File:69c2c4d370787fd96b9af1c68260ed34 IPCC_AR6_WGIII_Box_9_1_Figure_1.png]]

'''Box 9.1, Figure 1 | SER framework applied to the building sector.''' Source: [[#Saheb--2021|Saheb (2021)]] .

Applying sufficiency principles to buildings requires (i) optimising the use of buildings, (ii) repurposing unused existing ones, (iii) prioritising multi-family homes over single-family buildings, and (iv) adjusting the size of buildings to the evolving needs of households by downsizing dwellings ( [[#Wilson--2005|Wilson and Boehland 2005]] ; [[#Duffy--2009|Duffy 2009]] ; [[#Fuller--2011|Fuller and Crawford 2011]] ; [[#Stephan--2013|Stephan et al. 2013]] ; [[#Huebner--2017|Huebner and Shipworth 2017]] ; [[#Sandberg--2018|Sandberg 2018]] ; [[#McKinlay--2019|McKinlay et al. 2019]] ; [[#Ellsworth-Krebs--2020|Ellsworth-Krebs 2020]] ; [[#Berrill--2021|Berrill et al. 2021]] ) (Box 9.1, Figure 2).

Sufficiency is not a new concept, its root goes back to the Greek word ''sôphrosunè'' , which was translated in Latin to ''sobrietas'' , in a sense of ''enough'' ( [[#Cézard--2019|Cézard and Mourad 2019]] ). The sufficiency concept was introduced to the sustainability policy debate by ( [[#Sachs--1993|Sachs 1993]] ) and to academia by ( [[#Princen--2003|Princen 2003]] ). Since 1997, Thailand considers sufficiency, which was framed already in 1974 as Sufficiency Economy Philosophy, as a new paradigm for development with the aim of improving human well-being for all by shifting development pathways towards sustainability ( [[#Mongsawad--2012|Mongsawad 2012]] ). The Thai approach is based on three principles (i) moderation, (ii) reasonableness, and (iii) self-immunity. Sufficiency goes beyond the dominant framing of energy demand under efficiency and behaviour. Sufficiency is defined as avoiding the demand for materials, energy, land, water and other natural resources while delivering a decent living standard for all within the planetary boundaries ( [[#Saheb--2021|Saheb 2021]] b, Princen 2005) '''.''' Decent living standards are a set of essential material preconditions for human well-being which includes shelter, nutrition, basic amenities, health care, transportation, information, education, and public space ( [[#Rao--2012|Rao and Baer 2012]] ; [[#Rao--2018|Rao and Min 2018]] ; [[#Rao--2019|Rao et al. 2019]] ). Sufficiency addresses the issue of a fair consumption of space and resources. The remaining carbon budget, and its normative target for distributional equity, is the upper limit of sufficiency, while requirements for a decent living standard define the minimum level of sufficiency. Sufficiency differs from efficiency in that the latter is about the continuous short-term marginal technological improvements which allow doing more

with less in relative terms without considering the planetary boundaries, while the former is about long-term actions driven by non-technological solutions (i.e., land-use management and planning), which consume less in absolute-term and are determined by the biophysical processes ( [[#Princen--2003|Princen 2003]] ).

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[[File:e6b3104bf0f6a7427db907db7f4c01cf IPCC_AR6_WGIII_Box_9_1_Figure_2.png]]

'''Box 9.1, Figure 2 | Sufficiency interventions and policies in the building sector.''' Source: [[#Saheb--2021|Saheb (2021)]] .

Downsizing dwellings through cohousing strategies by repurposing existing buildings and clustering apartments when buildings are renovated and by prioritising multi-family buildings over single-family homes in new developments ( [[#Wilson--2005|Wilson and Boehland 2005]] ; [[#Duffy--2009|Duffy 2009]] ; [[#Fuller--2011|Fuller and Crawford 2011]] ; [[#Stephan--2013|Stephan et al. 2013]] ; [[#Huebner--2017|Huebner and Shipworth 2017]] ; [[#Sandberg--2018|Sandberg 2018]] ; [[#McKinlay--2019|McKinlay et al. 2019]] ; [[#Ellsworth-Krebs--2020|Ellsworth-Krebs 2020]] ; [[#Ivanova--2020|Ivanova and Büchs 2020]] ; [[#Berrill--2021|Berrill and Hertwich 2021]] ) are among the sufficiency measures that avoid the demand for materials in the construction phase and energy demand for heating, cooling and lighting in the use phase, especially if the conditioned volume and window areas are reduced ( [[#Duffy--2009|Duffy 2009]] ; [[#Heinonen--2014|Heinonen and Junnila 2014]] ). Less space also means less appliances and equipment and changing preferences towards smaller ones ( [[#Aro--2020|Aro 2020]] ). Cohousing strategies provide users, in both new and existing buildings, a shared space (i.e., for laundry, offices, guest rooms and dining rooms) to complement their private space. Thus, reducing per capita consumption of resources including energy, water and electricity ( [[#Klocker--2012|Klocker et al. 2012]] ; N. [[#Klocker--2017|Klocker 2017]] ), while offering social benefits such as limiting loneliness of elderly people and single parents ( [[#Wankiewicz--2015|Wankiewicz 2015]] ; [[#Riedy--2019|Riedy et al. 2019]] ). Senior cooperative housing communities and eco-villages are considered among the cohousing examples to scale-up ( [[#Kuhnhenn--2020|Kuhnhenn et al. 2020]] ). Local authorities have an important role to play in the metamorphosis of housing by proposing communal spaces to be shared ( [[#Williams--2008|Williams 2008]] ; [[#Marckmann--2012|Marckmann et al. 2012]] ) through urban planning and land-use policies ( [[#Duffy--2009|Duffy 2009]] ; [[#Newton--2017|Newton et al. 2017]] ). Thus, encouraging inter-generational cohousing as well as interactions between people with different social backgrounds ( [[#Williams--2008|Williams 2008]] ; [[#Lietaert--2010|Lietaert 2010]] ). Progressive tax policies based on a cap in the per-capita floor area are also needed to adapt the size of dwellings to households’ needs ( [[#Murphy--2015|Murphy 2015]] ; Akenji 2021).

Efficiency, and especially energy efficiency and more recently resource efficiency, and the integration of renewable to buildings are widespread concepts since the oil crisis of the seventies, while only most advanced building energy codes consider sufficiency measures ( [[#IEA--2013|IEA 2013]] ). Efficiency and renewable technologies and interventions are described in Sections 9.4 and 9.9.

A systematic categorisation of policy interventions in the building sector through the SER framework (Box 9.1, Figure 1) enables identification of the policy areas and instruments to consider for the decarbonisation of the building stock, their overlaps as well as their complementarities. It also shows that sufficiency policies go beyond energy and climate policies to include land-use and urban planning policies as well as consumer policies suggesting a need for a different governance including local authorities and a bottom-up approach driven by citizen engagement.

Compared to AR5, this assessment introduces four novelties (i) the scope of CO 2 emissions has been extended from direct and indirect emissions considered in AR5 to include embodied emissions, (ii) beyond technological efficiency measures to mitigate GHG emissions in buildings, the contribution of non-technological, in particular of sufficiency measures to climate mitigation is also considered, (iii) compared to the IPCC Special Report on Global Warming of 1.5°C (SR1.5), the link to sustainable development, well-being and decent living standard for all has been further developed and strengthened, and finally (iv) the active role of buildings in the energy system by making passive consumers prosumers is also assessed.

COVID-19 emphasised the importance of buildings for human well-being, however, the lockdown measures implemented to avoid the spread of the virus has also stressed the inequalities in the access for all to suitable and healthy buildings, which provide natural daylight and clean air to their occupants (see also Cross-Chapter Box 1 in Chapter 1). COVID-19 and the new health recommendations (World Health Organization 2021) emphasised the importance of ventilation and the importance of indoor air quality ( [[#Sundell--2011|Sundell et al. 2011]] ; [[#Nazaroff--2013|Nazaroff 2013]] ; [[#Fisk--2015|Fisk 2015]] ; [[#Guyot--2018|Guyot et al. 2018]] ; [[#Wei--2020|Wei et al. 2020]] ). The health crisis has also put an emphasis on preventive maintenance of centralised mechanical heating, ventilation, and cooling systems. Moreover, the lockdown measures have led to spreading the South Korean concept of ''officetel'' (office-hotel) ( [[#Gohaud--2017|Gohaud and Baek 2017]] ) to many countries and to extending it to ''officetelschool'' . Therefore, the projected growth, prior to the COVID-19, of 58% of the global residential floor area by 2050 compared to the 290 billion m² yr –1 in 2019 might well be insufficient. However, addressing the new needs for more residential buildings may not, necessarily mean constructing new buildings. In fact, repurposing existing non-residential buildings, no longer in use due to the expected spread of teleworking triggered by the health crisis and enabled by digitalisation, could be the way to overcome the new needs for ''officetelschool'' triggered by the health crisis.

The four novelties introduced in this assessment link the building sector to other sectors and call for more sectoral coupling when designing mitigation solutions. Guidelines and methodologies developed in Chapters 1, 2, 3, 4 and 5 are adopted in this chapter. Detailed analysis in building GHG emissions is discussed based on [[IPCC:Wg3:Chapter:Chapter-2|Chapter 2]] and scenarios to assess future emissions and mitigation potentials were selected based on Chapters, 3 and 4. There are tight linkages between this chapter and Chapter 6, 7, 8, 10 and 11, which are sectoral sectors. This chapter focusses more on individual buildings and building clusters, while [[IPCC:Wg3:Chapter:Chapter-8|Chapter 8]] discusses macro topics in urban areas. Findings of this chapter provides contribution to cross-sectoral prospection (Chapter 12), policies (Chapter 13), international cooperation (Chapter 14), investment and finance (Chapter 15), innovation (Chapter 16), and sustainable development (Chapter 17).

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