Save Embodied Carbon
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Saving Embodied Carbon through
Strengthening Existing Housing

4.8 gigatons of CO2 emissions can be saved while addressing the more than 268 million inadequate houses globally.


Build Change is the global leader for systems change in resilient housing. For almost two decades, we have been working to protect people and their livelihoods by preventing housing loss caused by disasters and climate-induced events. We work to transform the systems for regulating, financing, building, and improving houses around the world. Since 2004, Build Change has made over 1 million people and 200,000 buildings safer in over 25 countries.

The people we work with, from homeowners to policymakers and housing financiers, are already experiencing the catastrophic effects of climate change. They are facing more frequent windstorms, a higher proportion of which are more severe, and more intense rainfall with higher flood levels.

Build Change in Haiti
Engineers and builders embark on a home strengthening project in Haiti.

Adapting housing to be more resilient to climate change is an essential part of human survival of the climate crisis. But, in addition to adapting to the reality of climate change, we also want to minimize and slow the impact housing has on contributing to the causes of global warming.

Build Change first began working with governments, implementation partners, and homeowners to reuse and improve existing housing in Haiti following the 2010 earthquake near Port-au-Prince. The success of the program led us to apply the same approach to our other programs around the world and focus on improving housing that already exists, rather than building new.

Our experience in improving existing housing and the many benefits of doing so through homeowner-driven implementation models are documented in two existing Build Change publications:

  • The Build Change Guide to Resilient Housing, an operational manual with case studies written to communicate our model for making housing resilient and to serve as a practical guide for those who work in pursuit of this goal.
  • The Cost of Improving Vulnerable Housing, a comprehensive analysis of the cost of improving vulnerable homes, drawing on close to 1,500 retrofit designs from housing in fourteen countries across Asia, the Pacific, Latin America, and the Caribbean.

Recently we have begun to ask ourselves if we could quantify the environmental benefits. Could we apply established methods for calculating the emissions associated with building materials and construction to the post-disaster contexts in which we work? Could we do the same for preventative housing improvement programs in informal settlements?

The impetus of this study was to answer these questions. The subsequent analysis of our existing data sets has produced a number of important findings and recommendations that we use internally to inform decision-making by our engineers and designers, and externally to better communicate to homeowners and program partners the environmental benefits of improving existing housing. Above all, we want these findings to contribute to the global understanding of the benefits of reusing existing housing by providing data from novel contexts: post-disaster reconstruction and disaster prevention programs for self-built housing in informal settlements.

This report distills these findings into the third in our series of Build Change publications on improving existing housing. It presents the environmental benefits of upgrading existing housing rather than building new, based on analysis of the data set we have developed of our housing improvement programs in six countries around the world.

Executive Summary

The most sustainable house in the world is the home that has already been built. Assuming, of course, that the house has been made disaster-resilient.

Buildings and construction together account for almost 40 percent of energy-related carbon dioxide emissions, with housing accounting for at least 17 percent of the total.[1] While the benefits of retrofitting housing have long been known for increasing homeowner satisfaction, reducing construction-related costs, and strengthening local economies, little attention has been given to the environmental impact of a housing improvement intervention.

For housing built in informal markets, that is, housing constructed outside of regulation and government oversight, this study answers the question: how much embodied carbon can be saved by improving houses for disaster resilience?

This publication is the latest in a series authored by Build Change on strengthening and upgrading existing housing. Published in 2021, The Build Change Guide to Resilient Housing: An Essential Handbook for Governments and Practitioners serves as an operational manual and series of case studies in the operationalization of resilient housing programs. The Cost of Improving Vulnerable Housing, published in 2022, outlines the cost benefits and savings associated with improving existing housing for resilience.

As the third in this series, and informed by cases drawn from Build Change’s work in Colombia, Haiti, Honduras, Nepal, Philippines, and Sint Maarten and a total of 335 built projects, Saving Embodied Carbon Through Strengthening Existing Housing provides compelling evidence that improving existing housing significantly avoids carbon emissions in the housing construction value chain, thereby having substantial implications for achieving net zero in the built environment. By applying the findings from this study, we estimate there's an opportunity to save 4.8 gigatons of CO2 emissions while addressing the more than 268 million inadequate houses[2] globally.

Our intention is to contribute to global knowledge and research on the embodied carbon resulting from housing retrofits, upgrades, and improvements as well as new housing construction. In doing so, stakeholders across the housing value chain, including engineers and construction officials, policymakers, financiers, and advocates, can advance sustainable solutions to reduce the qualitative housing deficit and ensure provision of resilient housing.

Key findings include:

Build Change Key Finding

Improving a house instead of building a new one saves two-thirds of embodied carbon of an equivalent new house, and, on average, saves 18 metric tons of carbon dioxide. For the same embodied carbon budget of one new house, more than three houses can be improved and made safer.

Build Change Key Finding

Even if vertical expansion is included in the intervention, creating an additional living space or unit, it is still more carbon-efficient to improve existing housing rather than build new. With vertical expansion (e.g. adding a second story), improving existing housing still uses, on average, 47 percent less embodied carbon than an equivalent new house, meaning that the savings are doubled.

Build Change Key Finding

It is more carbon-efficient to improve an existing house before a disaster—even when the house is also expanded—than wait until it is destroyed and has to be rebuilt. Embodied carbon savings for a preventative upgrade are, on average, 61 percent higher than a post-disaster upgrade (without expansion). When the house is also expanded vertically, savings are still 26 percent higher if the upgrade is done preventatively.

Figure 1: The Costs of Inaction

Policymakers play a critical role in shaping the regulatory environment for prioritization of embodied carbon reduction in the housing sector through retrofitting. Based on the findings from this study there are a number of important actions that can be taken to advance overall resilience and embodied carbon savings in the housing sector. Most critically, these include:

Build Change Recommendation

Retrofit houses to withstand disaster. Policymakers should prioritize retrofitting existing housing as an effective strategy for both climate change adaptation and mitigation. The best way to balance the urgent needs for more housing, resilient housing, and green housing, while minimizing greenhouse gas (GHG) emissions, is to upgrade the existing housing stock.

Build Change Recommendation

Act now! Governments and homeowners should retrofit preventatively, before a disaster, to save even more emissions. The additional materials required for building repair in post-disaster scenarios significantly increases the emissions. Policies should incentivize mitigation before the next disaster.

Build Change Recommendation

Advance actions which prioritize housing upgrades within climate commitments, such as NDCs or building sector roadmaps, as well as national urbanization frameworks. With the next round of updates to Nationally Determined Contributions (NDCs) in 2025, the moment is ripe for integrating ambitious goals into climate planning. Governments should include housing upgrade plans within national frameworks for urban development and climate mitigation and adaptation, as well as within provisions for incremental upgrading within building codes. Advancing data through this study, and subsequently promoting action and leadership to reduce embodied carbon in the built environment—and in housing specifically—will be critical to shape the future of mitigation efforts, as well as provide the housing needed to meet the increasing requirements of a changing environment and global population.

1.0 Introduction: Two Conflicting Global Challenges

Globally, we need more housing—and we need better housing.

UN-Habitat estimates that 40 percent of the world’s population will need access to adequate housing by 2030, which translates into a demand for 96,000 new housing units every day.[3] Growing populations are driving a need for more housing in absolute terms. This is particularly true in cities, because of unceasing rural to urban migration.

This quantitative deficit goes hand in hand with the qualitative housing deficit, meaning there is an equal or greater need to improve the units that already exist. For example, neighborhoods may need connection to fresh water and sanitation infrastructure, or buildings may need to be strengthened and improved to better withstand earthquakes and climate extremes.

A critical component of reducing the qualitative housing deficit is increasing disaster resilience. Natural hazards alone do not cause disasters. Disasters develop when a natural hazard occurs in a location of high population exposure, and are exacerbated by social, financial and environmental vulnerabilities. The many barriers to resilient housing, including those caused by policy, money, and technology, mean it is common for housing to have been inadequately designed or built to resist natural hazards. Seventy-seven percent of fatalities from the deadliest earthquakes in the last 100 years were due to the collapse of masonry structures.[4]

Unfortunately, the risk from natural hazards is not static. Climate change is creating new hazards, exacerbating existing ones,[5] and multiplying the exposure to hazards.[6] Furthermore, the growing climate risk does not affect all people equally. Countries and populations with minimal historical emissions—such as small island developing states and indigenous communities—are disproportionately affected by the adverse effects of climate change,[7] resulting in serious threats to their homes.

We also need to significantly reduce both the embodied and operational greenhouse gas emissions associated with housing.

The UN Environment Global Status Reports conclude that buildings and construction together account for almost 40 percent of energy-related carbon dioxide emissions, with housing accounting for at least 17 percent of the total (See Figure 2).[8] To meet global climate ambitions set out in the Paris Agreement, the global buildings and construction sector must almost completely decarbonize by 2050. The energy intensity per square meter of the global buildings sector needs to improve on average by 30 percent by 2030 (compared to 2015).

At the same time, Dr. Fatih Birol, head of the International Energy Agency, recently noted that the world is expected to build 230 billion square meters of new construction over the next 40 years—adding the equivalent of the city of Paris to the planet every single week.[9]

Figure 2: Share of global energy-related CO2 emissions by sector

'use client'

Source: United Nations Environment Programme

Emissions associated with buildings and construction are split into two groups: embodied carbon emissions and operational carbon emissions.

To date, the global focus has been to prioritize reductions in operational emissions from buildings and construction, a logical initial response when operational emissions have traditionally accounted for a higher proportion of total emissions. Globally, investment in the energy efficiency of buildings is rising, reaching more than USD 180 billion in 2020—a 40 percent increase since 2015.8 Regulation is also increasing: 63 percent of countries now include measures for energy efficiency improvements in buildings as part of their Nationally Determined Contributions and 81 countries now have mandatory or voluntary building energy codes (compared to 62 countries in 2015).[10]

However, because focus has been on operational instead of embodied carbon emissions, embodied emissions now account for a much larger proportion of total building lifetime emissions. In some countries,embodied carbon may soon approach 100 percent of the total and can already account for 40–70 percent of whole life carbon in a new low-carbon building.[11]

How do we balance the needs for more housing, resilient housing, and green housing?

The urgent need for more and better housing often appears to be at odds with demanding schedules for emissions reductions targets in buildings and construction. Adequate housing is an essential precursor for economic prosperity, health and wellbeing, and equitable development. But if no changes are made to housing production, the environmental cost of providing for such a large proportion of the global population will be disastrously high.

Inherent to disaster-resilient housing is resistance against damage from natural hazards such as hurricanes, floods, fires, and earthquakes. However, the additional demands these kinds of loads place on a structure are not immediately complementary to efforts towards lower carbon, more efficient design. There is growing evidence that when the full life cycle and life span of a building is considered, it is neither sustainable nor economical to build structures that will be damaged beyond repair during expected hazard events, and thus require complete replacement with new building materials.

Box 1: Embodied Carbon and Earthquakes in New Zealand. Following the 2010-2011 Canterbury, New Zealand earthquakes, 60 percent of multistory buildings in the Christchurch central business district were demolished. Using a dataset of 142 demolished concrete buildings, researchers at the University of Auckland found that the total embodied carbon, now beyond reuse and deposited in a landfill, was equivalent to the emissions from the electricity purchased by 20 percent of the dwellings across the country in a year.[12]

Harnessing the potential of “Build Less”

In the Hierarchy of Net Zero Design (see Figure 3), enormous potential exists to reduce embodied carbon in the built environment by applying the “Build Less” approach to housing. This category, which has the second highest potential to create savings next to “build nothing”, includes repurpose, refurbish, and reuse. Strengthening and improving an existing home to withstand disaster fits perfectly in this category.

Figure 3: The Hierarchy of Net Zero Design

Source: IStructE (IStructE, 2022)

2.0 Overview of the Dataset and Analysis Approach

This report presents a first-of-its-kind international data set on the embodied carbon savings impacts of improving existing housing to withstand disaster.

The dataset spans six countries across four continents. The embodied carbon savings are estimated by comparing 275 existing home strengthening projects with 60 new disaster-resilient housing projects in the same countries. All 335 homes have been built or retrofitted by Build Change or our partners, meaning the analysis was based on the final, measured quantities of materials that went into each house.

Comparing the home retrofits against disaster-resilient new construction was the favored approach for a number of reasons:

  • In most cases, new construction is the most likely alternative to retrofitting. In both post-disaster and prevention contexts, the misperceived challenges of improving existing housing most often result in governments, the private sector and aid agencies opting to build new rather than improve existing housing.

  • The relative approach standardizes the results and allows compilation and comparison at a global scale. Build Change’s retrofit interventions vary considerably depending on the local context, but by always comparing the retrofit to an equivalent new construction we are able to aggregate the results and draw global conclusions.

  • Considering the results relative to a baseline addresses many of the challenges of uncertain or absent data. In the countries highlighted in this study, there is a scarcity of data on embodied carbon of building materials. By using the same data for emissions calculations of retrofit and new construction houses, this analysis ensures that the emphasis is on the difference between the two scenarios.

Our analysis considers the “upfront carbon”, referred to as lifecycle stages A1 to A5 in Figure 4, for both the retrofit homes and the new construction homes. Whether a home is disaster resilient because it was retrofitted or newly built does not significantly impact the emissions associated with the use and end-of-life phases, so the emissions associated with stages B and C are canceled out when comparing retrofit with new construction.

Figure 4: Building Life-Cycle Assessment Phases

Source: RMI

To account for differences in the data sample size from different countries, the houses were grouped into 16 different design groups. Every house within a design group shares key characteristics, such as location, construction type, performance target, hazards considered, and disaster context. Sample designs within the same design group were averaged to determine an overall representative set of carbon costs for each group.

Figure 5: Countries and Their Respective Sample Size (Number of Houses) Represented in Dataset

Source: Build Change

3.0 Key Findings

Build Change Key Finding

Improving an existing house, instead of building a new one, saves 18 metric tons of carbon dioxide.

On average, 18 metric tons of carbon dioxide are saved per house.

This is more than one person’s total annual emissions in the US or 60 people’s total annual emissions in Haiti.[13]

Figure 6: The Relative Cost of Embodied Carbon Savings in a Single House