UN plan promises large carbon dioxide emission cuts in construction sector

Rapid urbanization worldwide means every five days, the world adds buildings equivalent to the size of Paris, with the built environment sector already responsible for 37 percent of global emissions. A report published today by the UN Environment Programme (UNEP) and the Yale Center for Ecosystems + Architecture (Yale CEA), under the Global Alliance for Buildings and Construction (GlobalABC), offers solutions to decarbonize the buildings and construction sector and reduce the waste it generates.

The report, Building materials and the climate: Constructing a new future, offers policy makers, manufacturers, architects, developers, engineers, builders and recyclers a three-pronged solution to reduce "embodied carbon" emissions and the negative impacts on natural ecosystems from the production and deployment of building materials such as cement, steel, aluminum, timber, and biomass:

• Avoid waste through a circular approach: building less by repurposing existing buildings is the most valuable option, generating 50-75 percent fewer emissions than new construction; promote construction with less materials and with materials that have a lower carbon footprint and facilitate reuse or recycle.
• Shift to ethically and sustainably sourced renewable bio-based building materials, including timber, bamboo, and biomass. The shift towards properly managed bio-based materials could lead to compounded emissions savings in many regions of up to 40 percent in the sector by 2050. However, more policy and financial support is needed to ensure the widespread adoption of renewable bio-based building materials.
• Improve decarbonization of conventional materials that cannot be replaced. This mainly concerns the processing of concrete, steel, and aluminum—three sectors responsible for 23 percent of overall global emissions today—as well as glass and bricks. Priorities should be placed on electrifying production with renewable energy sources, increasing the use of reused and recycled materials, and scaling innovative technologies. Transformation of regional markets and building cultures is critical through building codes, certification, labeling, and the education of architects, engineers, and builders on circular practices.

The three-pronged Avoid-Shift-Improve solution needs to be adopted throughout the building process to ensure emissions are slashed and human health and biodiverse ecosystems are protected. The solution also requires, in its implementation, sensitivity to local cultures and climates, including the common perception of concrete and steel as modern materials of choice.

"Until recently, most buildings were constructed using locally sourced earth, stone, timber, and bamboo. Yet modern materials such as concrete and steel often give only the illusion of durability, usually ending up in landfills and contributing to the growing climate crisis," said Sheila Aggarwal-Khan, Director of UNEP's Industry and Economy Division.

"Net zero in the building and construction sector is achievable by 2050, as long as governments put in place the right policy, incentives and regulation to bring a shift the industry action," she added.

To date, most climate action in the building sector has been dedicated to effectively reducing "operational carbon" emissions, which encompass heating, cooling, and lighting. Thanks to the growing worldwide decarbonization of the electrical grid and the use renewable energies, these are set to decrease from 75 percent to 50 percent of the sector in coming decades.

"Since the built environment sector is so complex, with interdependencies across actors, all hands on deck are required to decarbonize, and we can't leave anyone behind. Policies must support the development of new cooperative economic models across the building, forestry and agricultural industries, in order to galvanize a just transition towards circular, bio-based material economies that can also work synergistically with the conventional material sectors," according to lead author Anna Dyson, Founding Director of the Yale Center for Ecosystems and Architecture (Yale CEA).

Buildings contain materials produced in disparate regions across the globe; reducing "embodied carbon" emissions from production and deployment of building materials therefore requires decision-makers to adopt a whole life-cycle approach. This involves harmonized measures across multiple sectors and at each stage of the building lifecycle—from extraction t processing, installation, use, and demolition.

Government regulation and enforcement is also required across all phases of the building life cycle—from extraction through end-of-use—to ensure transparency in labeling, effective international building codes, and certification schemes. Investments in research and development of nascent technologies, as well as training of stakeholders in the sectors, are needed, along with incentives for cooperative ownership models between producers, builders, owners, and occupants to the shift to circular economies.

Case studies from Canada, Finland, Ghana, Guatemala, India, Peru, and Senegal, demonstrate how decarbonization takes places using "Avoid-Shift-Improve" strategies: developed economies can devote resources to renovating existing aging buildings, while emerging ones can leapfrog carbon-intensive building methods to alternative low-carbon building materials.

Cities worldwide can drive the implementation of decarbonization. Many are already integrating vegetated surfaces, including green roofs, façades, and indoor wall assemblies to reduce urban carbon emissions and cool off buildings, increase urban biodiversity and more.

Building materials set to dominate CO₂ emissions and must be decarbonized

• Most climate action was dedicated to reducing "operational carbon" emissions of buildings (e.g, heating, cooling, lighting), set to decrease from 75% to 50% of the sector in coming decades.
• Climate action is needed to reduce "embodied carbon" emissions from production and deployment of building materials (e.g., cement, steel, and aluminum).
• To reach net zero emissions in the construction sector, future materials must be procured from renewable/reusable sources.
• New materials should be extracted using renewable electrification, and carbon capture and storage methods that require further research and development.
• If future building materials are derived from carbon capture, buildings could become carbon negative

A life-cycle approach to decarbonising the sector

• Consider impacts of material choices on human health and well-being, climate and ecosystems before the materials are even extracted, and then again at each phase of the building life cycle, from extraction to processing, installation, use and demolition.
• Access to reliable information, verification, and coordination across different stakeholders in the building sector—manufacturers, architects, engineers, builders and recyclers—is key
• Emerging economies can leapfrog carbon-intensive building methods of developed regions
• Developed economies can devote resources to renovating existing aging buildings, while emerging economies can shift to alternative low-carbon building materials
• Binding commitments are needed to ensure the cooperation of producers, growers, designers, builders, and owners along the supply chain.

Integrating living biomass systems in buildings

• Municipalities worldwide have recognized the benefits of integrating vegetated surfaces (green roofs and façades, indoor wall assemblies) to reduce urban carbon emissions and reclaim the benefits of nature lost through urbanization: can generate up to 60% energy savings compared with exposed concrete walls.
• Mandating use of vegetated surfaces to cover exposed concrete or asphalt would help naturally keep buildings cool, reduce energy consumption, and absorb storm water to reduce flooding, replenish water tables and urban biodiversity.

Three urgent pathways: Avoid unnecessary extraction and production, shift to regenerative materials, improve decarbonization of conventional materials.

• Avoid extraction and production of raw materials by galvanizing a circular economy: building with less materials through better data-driven design, while maximizing reuse/recycling of buildings.
• Avoiding unnecessary extraction and production requires rethinking the design of buildings, especially during planning and design.

Key circular economy design strategies:

• Digitalization (building information modeling and/or building passports) and computer-aided design optimization for less material usage.
• Design for disassembly" (decreasing 10-50% of GHG emissions)
• Selecting materials that reduce non-renewable material extraction, designing for material and component reuse.
• Good maintenance is the least-wasteful option, as renovation generates 50-75% fewer emissions than new construction.
• Early design choices greatly impact the ability to reuse or recycle materials later in the building cycle.
• Repurposing failing reinforced concrete from 20th-century infrastructure represents an under explored opportunity that requires further research and development.
• Shift to regenerative material practices wherever possible by using ethically produced low carbon earth- and bio-based building materials (e.g., sustainably sourced bricks, timber, bamboo, agricultural and forest biomass), and help to incentivize biodiversity.
• Improved land-use management is critical for any newly produced regenerative sources for buildings.

Improve non-renewable building materials and processes

• Key priorities are to improve processing of concrete and cement, steel and iron, and aluminum (responsible for 23% of overall global emissions today), plastics, glass, and bricks.
• Priority materials for decarbonization: concrete and cement, steel and iron, aluminum, plastics, glass, earth-based masonry

Challenges in the shift to regenerative materials

• Sensitivity to local cultures and climates. E.g., many cultures consider concrete and steel to be "modern" materials of choice.
• Ensure a socially-environmentally just transition to naturally sourced building materials
• Investment in the research and development of methods and standards
• Aligning stakeholders across the lifecycle: governments, cities, industry
• Countries with diverse built environments can pursue decarbonization

Case studies from Canada, Finland, Ghana, Guatemala, India, Peru, and Senegal, demonstrate how decarbonization takes places using "Avoid-Shift-Improve" strategies.

Provided by United Nations Environment Programme