City officials tasked with reducing and eliminating greenhouse gas emissions from their communities face a tricky task in estimating building emissions as they work to prevent the most harmful impacts of climate change. The biggest challenge is that there are there isn't consensus on an internationally accepted definition of Net Zero-Energy Buildings (NZEBs) and Zero-Carbon Buildings (ZCBs), as they are defined variously across geographies and government agencies. Complicating matters more, these definitions are updated from time to time by the International Energy Agency (IEA). At present, there is a worrisome potential that interchangeable use and unclear interpretations will result in different objectives, policy directions and outcomes for building decarbonization.

NZEBs are defined as buildings where total production of energy is equal to the overall consumption, even some buildings produce a surplus through solar PVs etc. (referred to as Net positive energy buildings). This reasoning assumes that cleaner electricity sources, or surplus power generation at the building site, results in the overall reduction of greenhouse gas emissions. However, this is only a partial consideration of operational energy and neglects what’s known as embodied emissions, which are released during various lifecycle stages throughout the lifetime of the building.

In contrast to this reasoning, a carbon-based life-cycle assessment (LCA) of buildings quantifies both operational and embodied emissions. Research suggests that the proportion of emissions in a building's overall life can fluctuate, depending on several parameters (project site, transportation of materials, etc.). Therefore, a NZEB may not achieve zero carbon emissions over its lifetime.

Figure showing types of carbon in buildings.

This calls for a need to understand efficient NZEBs and ZCBs through lifecycles and develop appropriate strategies for maximum carbon reduction at various stages. A strategic plan for reducing emissions rapidly through policy becomes critical in achieving large-scale impact. While reducing operational carbon through policy action has been the focus internationally, embodied carbon policies are just beginning to gain importance.

This document lists a series of tools for building LCAs and guidelines that can aid city officials in strengthening their capacity and creating their own strategies that are in line with national roadmaps (if any exist for their nation) or with national policies. 

It is recommended that a metric be used in a LCA for all building phases, including material extraction, construction and demolition. This should take into consideration greenhouse gas emissions, which are measured in terms of carbon dioxide equivalents.

A widely used methodology is shown below, which categorizes emissions into the product manufacturing stage (A 1-3), also called the design stage, followed by the construction stage (A 4-5), the operation stage (B 1-7) and finally the end-of-life stage (C 1-4).

Graphic showing The Life Cycles.

Some LCA tools, like openLCA, are available for free for the building and construction sector. Operating these tools requires technical expertise, therefore building the capacity of various stakeholders in the construction value chain is important. The Life Cycle Inventory database can be region sensitive and lack of data, quality, costs, regulatory mandates other than technical capacity also hinder application of these tools.

  • One Click LCA: One Click LCA is used for calculations across all life-cycle stages from Cradle to Grave (production to end-of-life). It allows one to obtain outcomes that meet EN and ISO standards, LEED, BREEAM and more than 40 other certifications. LCA Academy also offers free training modules.  
  • Tally: To compare different design possibilities and study the environmental impact of building materials, architects and engineers using the Revit® program (a Building Information Modelling [BIM] software) can use the Tally application. EC3/Embodied Carbon Calculator is another tool that is often used with Tally for comparing the embodied carbon of various building materials, to make informed choices right at the design stage for new as well as refurbishment projects. 

Transformative Actions and Implementation

National roadmaps are being developed around the globe based on approaches present in guidance documents like Global Roadmap for Buildings and Construction 2020-2050. Cities are also in the process of developing climate action plans and decarbonization strategies for various sectors. Following are some documents that can aid planning for building decarbonization: 

  • 2022 Global Status Report for Buildings and Construction: This document lists progress on national roadmaps for building decarbonization across various nations, especially focusing on building materials, explores several case studies and provides key recommendations for policymakers. 
  • Carbon Leadership Forum Policy Toolkit: Carbon Leadership Forum launched an embodied carbon policy toolkit which comprises of procurement policies, climate action plans, building codes and regulations, fiscal and non-fiscal incentives, and material reuse guidelines. It intends to provide decision-makers, business leaders and environmentalists with a carefully crafted package to direct the development of decarbonization policies at local, state and federal levels. 
  • Adopting Decarbonization Policies for the Buildings and Construction Sector: This handbook provides a practical overview of the alternatives for procuring sustainable buildings and construction in developing countries and emerging economies. It also lists case studies across housing and commercial building types — where reductions in energy consumption were achieved — and provides recommendations for participatory planning, developing a financing strategy, influencing user behavior and more.
  • Buildings and Climate Change Adaptation - A Call for Action: This manual promotes awareness of and suggests solutions for climate change issues in the real estate, building and construction (RBC) industries. This document is one of the first to discuss both the advantages of the RBC sector's activities and the difficulties with climate change adaptation.
  • Green Building: A Financial Blueprint for Emerging Markets: This document looks at the responsibilities of governments, as well as green building developers and owners who are crucial in creating a market for green construction. It also lists barriers like the perception of high construction costs, a lack of incentives and benefits, alignment of values among market participants, and an imbalance between the relatively short hold periods of real estate assets in portfolios and the lengthy lifespans of buildings. 
  • Handbook of Sustainable Building Policies: Policymakers and professionals can use this handbook as a reference guide to learn about different policy instruments and how they relate to one another. The handbook presents 25 different policy instruments, under the following headings:     
    • Regulatory-normative (e.g., building codes and standards)  
    • Regulatory-informative (e.g., certification and labeling programs)  
    • Economic and market-based (e.g., preferential mortgages or carbon market mechanisms)  
    • Fiscal instruments and incentives (e.g., taxes, subsidies or loans)  
    • Support, information and voluntary action (e.g., public leadership programs for awareness)  

Cities are often seen as leaders in climate governance when they implement experimental policies. ​While multi-level governance is crucial, city autonomy and capacity along with non-state actor’s participation can speed up the decarbonization of all sectors, including the construction industry. Most of the tools and guidelines listed here are available free of cost and can inform various decisions by stakeholders across the construction value chain. These include architects, urban planners, state officials (for planning and design commissioning), private investors, material manufacturers and more. Decarbonizing construction activities, if done judiciously, can become a profitable business and help yield both financial and environmental benefits.