Eighty percent of existing U.S. buildings will still be in use by 2050, but many are highly inefficient and reliant on fossil fuels. Retrofitting existing buildings is a vital strategy to improve building performance and reduce climate-warming pollution; the operation of buildings accounts for 28 percent of global greenhouse gas emissions. Deep-energy retrofits that improve the efficiency of building envelopes and incorporate high-performance mechanical systems can achieve reductions of 50 percent or more in both building energy consumption and operating emissions.
Investing in retrofits can also lead to 50 to 75 percent fewer embodied-carbon emissions compared to demolishing and reconstructing properties. However, careful consideration must be given to any upfront embodied- carbon emissions associated with materials used for retrofits because these emissions can offset retrofit operational-emission reductions. Strategic material selection that focuses on low-carbon or carbon-storing products is crucial for optimizing climate benefits.
To explore this approach, RMI (formerly Rocky Mountain Institute) recently published a report titled, “Transforming Existing Buildings from Climate Liabilities to Climate Assets”. It offers a comprehensive strategy that combines analyses of operating- and embodied-carbon emissions. The report is available for download.
BUILDING RETROFITS AND THEIR BENEFITS
Retrofitting strategies that prioritize energy-load reductions, electrification, and renewable-energy production can eliminate operational emissions and mitigate the impact of electrification on the grid. However, the physical retrofit work necessary to reduce operating emissions can result in an embodied-carbon impact that can be mitigated by integrating best practices and strategic material selection.
Deep-energy retrofits are especially important in cold and mixed-humidity climates, where they reduce thermal loads from high-emitting buildings. These retrofits involve super-insulating building shells, implementing high-performance all-electric mechanical systems, incorporating additional energy-efficiency measures and integrating renewable-energy sources. They offer additional benefits, such as improved comfort, reduced vulnerability to fossil-fuel price fluctuations and increased resilience during power outages.
UNDERSTANDING EMBODIED CARBON
In recent years, embodied-carbon emissions, which account for 11 to 21 percent of global emissions, have gained attention alongside operational emissions because both types of emissions are critical levers for addressing climate change. In the RMI report, we specifically look at emissions from raw-material harvesting and manufacturing of building products or materials that would be used in retrofits. This production phase of building materials is considered the “cradle to gate” phase of embodied carbon.
This phase represents a significant upfront spike in emissions that can offset the operating-emissions reductions achieved through retrofits. In this decisive decade, industry professionals should take a holistic approach to building decarbonization and focus on managing and mitigating these emissions. Although the referenced RMI report primarily examines the “cradle to gate” phase,
other subsequent phases that cause embodied-carbon emissions, such as construction methods, waste, maintenance and disposal, should also be considered to evaluate the full climate impact of retrofit projects.
RMI REPORT: LOW-EMBODIED-CARBON PRODUCTS IN RETROFITS
Material considerations are especially important in cold and mixed-humidity climates that require more intensive exterior insulation systems to cut thermal loads. Many retrofits use high-embodied- carbon materials, like foam insulation, to reduce operating emissions. RMI’s research demonstrates that materials specified for the insulation component of the assembly can have a significant impact on the total embodied carbon of retrofit projects.
Through the case-study analysis, the report compares the results from three different rigid insulation boards, achieving the same thermal performance for a deep-energy retrofit. The results showed that of the three scenarios, one product would realize net-emissions-reduction benefits after seven years, one after three years, and one would facilitate an immediate benefit from operating-emissions reductions and provide potential for storing carbon (see the graph below).
Key takeaways from this research include:
- Deep-energy retrofits in cold climates generally have an embodied-carbon impact equivalent to two to seven years of operating-carbon reductions.
- Low-carbon and carbon-storing materials are available today within different construction methodologies that significantly reduce this timeframe and enable immediate climate benefits. View Appendix C in RMI’s report for a list of these materials.
- A combined analysis considering anticipated operating-carbon emissions reductions and the embodied-carbon impact of the assembly design allows for the best achievable climate impact.
The analysis demonstrates that with the implementation of an exterior insulation system with mid-range global-warming potential, the embodied-carbon emissions associated with the deep-energy retrofit delay full realization of operating-emissions reductions to less than three years. In the worst-case scenario with using higher-embodied carbon materials, this timeframe is postponed further. Despite this delay, retrofitting buildings remains an effective strategy to reach climate goals, especially compared to replacing them with new traditional construction. In best-case scenarios, where carbon-storing materials can be used in the retrofit, there is no emissions spike at all, operating-carbon reductions are realized immediately, and the existing building can store carbon for the remainder of its lifetime.
AN IMMEDIATE NEED TO ADDRESS EMBODIED CARBON IN RETROFITS
The widespread use of carbon-storing materials in deep-energy retrofits would transform existing buildings from carbon emitters to carbon-storing buildings. Waiting four to six years for emissions reductions from deep-energy retrofits leaves us with insufficient time to meet global climate targets and avoid the worst outcomes. Instead, we must accelerate widespread adoption of low-carbon materials in retrofits to achieve a net-zero building sector.
Innovators, manufacturers and design professionals are needed now more than ever to propel the industry forward with new materials, products, and design and construction services that ratchet down upfront embodied-carbon emissions so that retrofitted buildings can achieve operating emissions savings as quickly as possible. RMI’s initiatives—REALIZE-MA and the Advanced Building Construction Collaborative—provide expertise and promote collaboration for scalable solutions. However, this transition requires far greater public and private-sector support, incentives and resources for stakeholders.
Policymakers have the ability to shorten the path to achieving this future by supporting investment in low-embodied-carbon products, carbon-storing materials and deep-energy retrofit solutions. Supportive legislation and financial assistance to standardize environmental product declarations, increase material transparency and identify low-carbon construction alternatives are urgently needed. It’s time to seize this opportunity to retrofit aging and inefficient buildings with low-embodied carbon materials. Together we can reduce climate pollution, create jobs, and provide better buildings while simultaneously tackling both embodied- and operational-carbon emissions in the built environment.