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Net Zero Resource Hub

Section 1: Why is it important to decarbonise construction and achieve net zero

Climate emergency and the need to reach net zero carbon

Summary

  • The existing climate pledges are inadequate to meet the climate targets.
  • To limit global warming to 1.5°C, greenhouse gas emissions (GHG) have to be reduced by 45% by 2030.
  • Decarbonization of the building sector is essential to meet the climate targets
  • Construction materials such as cement, steel, aluminum, and plastics are major contributors to embodied carbon.
  • In a building, structural elements and finishes are the major contributors to embodied carbon.
  • Introduction to net-zero carbon concepts, drivers, and strategies to achieve it.

Alarming emission trends

According to UNEP’s most recent Emissions Gap Report 2022, global GHG emissions must be reduced by 30% and 45% to limit global warming to below 2.0°C and 1.5°C, respectively. For the 1.5°C scenario, the full implementation of unconditional NDCs is estimated to result in a gap of 23 gigatons of carbon dioxide equivalent (GtCO2e). If the conditional NDCs are also fully implemented, the 1.5°C emissions gap is reduced to 20 GtCO2e. 

Fig 1. Current emission trends (Source: UNEP Emissions gap report, 2022)

Are the current climate pledges sufficient to stop a climate catastrophe?

Without additional action, current policies lead to global warming of 2.8°C before the end of this century. Implementation of unconditional and conditional Nationally Determined Contributions (NDC) scenarios reduce this to 2.6°C and 2.4°C respectively. Global warming levels only get close to the Paris Agreement temperature goal if net-zero pledges are fully implemented

Why should we focus on the building sector?

Buildings are responsible for 39% of global carbon emissions, out of which 28% are from operational emissions, and 11% are from construction materials-related emissions. Decarbonization of the building sector is critical in limiting global warming to 1.5°C.

Embodied carbon emissions from the building sector

The global building floor area is expected to double by 2060 resulting in 100-200 gigatons of embodied carbon. Unlike operational carbon emissions, embodied carbon is locked in place upon construction. Therefore it is important to address embodied carbon emissions to achieve net zero goals.

Fig 2. Key construction material’s contribution to global emissions

(source: https://architecture2030.org/why-the-building-sector/)

The key construction materials concrete, steel, and aluminum are responsible for 23% of total global emissions (see Fig.2). The embodied carbon of these materials can be reduced through policy, design, material selection, and specification. The carbon budget available for key materials is 300Gt for 2100.  Low-carbon energy is not enough to meet this budget. Even with 100% low-carbon energy by 2050, emissions far exceed the available carbon budget (see Fig 3).
Fig 3. Carbon budget for 2100 (source: Circular economy- a powerful tool for climate mitigation)

Where do impacts come from in a typical building?

One Click LCA analyzed the distribution of embodied carbon by material category and building elements of approximately 500 Finnish buildings. The four most important construction material categories for embodied carbon are cement, steel, aluminum, and plastics (Fig.4). Of the remaining material categories, insulation, doors, windows, and glass products, and gypsum, cement, and mortar categories also stand out in importance. The results show that superstructural elements are the main contributors to embodied carbon of a building (Fig.5). The substructures and internal finishes are also major contributors.

Fig 4.  A1-A3 carbon footprint by material category (sample of approximately 500 Finnish buildings)
Fig 5.  A1-A3 carbon footprint by building element (sample of approximately 500 Finnish buildings)

Introducing net-zero concepts

Net zero carbon definitions

Net zero carbon – construction is achieved when the amount of carbon emissions associated with a building’s product and construction stages up to practical completion is zero or negative, through the use of offsets or the net export of on-site renewable energy.

Net zero carbon – operational energy is achieved when the amount of carbon emissions associated with the building’s operational energy on an annual basis is zero or negative. It is highly energy efficient and powered from on-site and/or off-site renewable energy sources, with any remaining carbon balance offset.

Net zero carbon – whole life is achieved when the number of carbon emissions associated with a building’s embodied and operational impacts over the life of the building, including its disposal, are zero or negative.

Carbon offsetting is the reduction in emissions of carbon dioxide or greenhouse gasses made in order to compensate for or to offset an emission made elsewhere.

Various net zero carbon commitments and measures

Many organizations and governments have taken initiatives to reduce carbon and reach their net zero goals. Listed below are a few of the various commitments undertaken to reach net zero carbon of the built environment.

Commitment  Details 
The net zero carbon buildings commitment, World Green Building Council By 2050, new buildings, infrastructure and renovations should have net zero embodied carbon, and all buildings, must be net zero operational carbon.
Advancing Net Zero , World Green Building Council  World GBC’s global program aims to promote and support the acceleration of net zero carbon buildings to 100% by 2050.
Advancing Net Zero, UK Green Building Council   Aims to drive net zero transition in the UK and deliver emission reductions. Ambitious are set out in the Net Zero Whole Life Carbon Roadmap
UK Net Zero Carbon Building Standard Cross-industry initiative to develop UK’s first net zero carbon standard. The participating organizations include BBP, BRE, the Carbon Trust, CIBSE, IStructE, LETI, RIBA, RICS, and UKGBC.
The AIA 2030 Commitment, American Institute of Architects Commitment to reach net zero emissions by 2030.
The 2030 Challenge for Embodied Carbon, Architecture 2030  Commitment to reach Zero GWP by 2040
Zero Carbon Certification, International living building institute Projects must demonstrate actual net zero carbon operations 

The total embodied carbon emissions of the final construction materials and processes associated with the project must be disclosed and accounted for through the procurement of equivalent carbon offsets.

Net Zero Carbon Buildings Accelerator, C40 Cities  Committed to enact regulations and/or planning policy to ensure new buildings operate at net zero carbon by 2030 and all buildings by 2050. 
2030 Climate Challenge, RIBA  Provides targets to reach net zero 

The website Net Zero Tracker provides a summary of Net Zero commitments made by various countries.

How to achieve net zero carbon?

The steps involved in achieving net zero are:

  1. Establish a net zero carbon scope: establish if your net zero carbon scope should include Net zero carbon- construction, operational energy, or whole-life carbon.
  2. Reduce construction impacts: whole life cycle assessment should be performed to reduce the impacts.
  3. Reduce operational energy use: prioritize reduction in operational energy consumption.
  4. Increase renewable energy supply: prioritize renewable energy sources.
  5. Offset any remaining carbon: remaining carbon should be offset using a recognized framework and publicly disclosed.

Strategies to achieve a meaningful reduction

There are two ways to approach carbon optimization:

  1. Target absolute benchmarks: For example the new London plan, Living building challenge, etc (for structure and foundation envelope)
  2. Set up a baseline: set up a baseline and work towards achieving reductions (%) from the baseline, for example, LEED.

In the next articles, we are going to explain the strategies adopted to reduce embodied carbon such as early carbon optimization, understanding the embodied carbon from construction material, and circularity in more detail.

Net Zero Resource Hub

Understanding the construction materials

Net Zero Resource Hub

Early carbon optimization

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