---

Executive Summary

Overview

The building sector contributes significantly to greenhouse gas (GHG) emissions. Reducing GHG emissions (also referred to as carbon emissions) from this sector is critical for Canada to achieve its climate targets.

In recent years, many real estate and asset management organizations have been setting near- and net-zero-carbon ambitions. However, many will be challenged to meet these targets without significant decarbonization of their existing buildings.

For many commercial buildings, there will need to be a decision between demolishing and rebuilding them, versus performing deep carbon retrofits. However, there is a lack of research comparing the full whole-life impact of these two options. Most assessments only focus on achieving energy efficiency and making links to potential operational carbon reductions.

Whole-life carbon emission assessments, on the other hand, consider both the operational and embodied carbon emissions of building projects. Embodied carbon emissions include emissions resulting from the manufacturing, transportation, installation, maintenance, and disposal of building materials.

This study aims to inform the commercial real estate (CRE) sector about the whole-life carbon impacts of extending building life – a key circular economy practice. Building on a more extensive review of the opportunities to apply circular strategies to commercial office buildings, this study also examines gaps in the research, data access and standardization, guidelines, standards, and tools that could help inform decisions about whether to demolish and rebuild, or retrofit, new commercial office buildings.

Review of Literature

A literature review of existing research, standards, guidelines and building life-cycle assessment (LCA) case studies was conducted. The LCA case studies reviewed found that the two options – retrofitting versus building new – resulted in comparable post-construction annual operational emissions.

However, retrofitting resulted in significantly less upfront embodied carbon emissions compared to building new. Retrofits had lower overall whole-life carbon than new construction in all but one case (that one case assumed a much shorter lifetime). Retrofits had a relatively short “carbon payback” period of three to five years for the upfront embodied carbon emissions investment associated with the retrofit, which was offset by annual operational emissions savings.

The review of LCA and circularity standards and guidelines found a lack of consistency on the aspects of LCA that could inform the decision between retrofitting versus rebuilding. The European standard EN 15804, Sustainability of construction works – Environmental product declarations, and its international counterpart, ISO 21930:2017, provide inconsistent guidance. EN 15804 requires the inclusion of end-of-life impacts or impacts beyond its life (stages C and D in LCA), whereas ISO 21930 does not include this requirement. Standards and guidelines for whole-building LCA (wbLCA) do not provide specific directions on the assumptions for an element’s lifetime or impacts from stages C and D when product- or project-specific data is missing. Finally, current building circularity standards and guidelines do not provide any direction on assessing their whole-life carbon impacts.

Canadian LCA Case Study

An LCA case study was conducted to include six buildings across three major Canadian cities – Toronto, Edmonton, and Vancouver – with two types of office buildings each – mid-rise and high-rise.

The LCA results showed that, in all scenarios, the decision to retrofit resulted in significantly lower whole-life emissions than the demolition and new construction option. These reductions were most significant when embodied carbon emissions constituted a larger portion of a project’s whole-life emissions. This was the case in higher-performance buildings in regions with a lower-carbon electricity grid, making the case for retrofit strongest in regions with green electricity, such as British Columbia, Quebec, Manitoba, PEI, Newfoundland, and Ontario.

It was found that a retrofit of these buildings led to a 26% to 70% lower whole-life carbon emissions than demolition and new construction by 2030, and 11% to 58% lower emissions by 2050. These reductions were mainly achieved by reusing the existing concrete structure when retrofitting.

In a sensitivity analysis, the retrofit option still showed lower whole-life carbon emissions even when compared to a modelled new mass-timber structure. However, the whole-life carbon emissions of the retrofit and new mass-timber building were similar when carbon stored in the wood of the timber structure was considered.

This finding was consistent with results from the literature review, suggesting that retrofit will likely outperform new buildings on life-cycle emissions, unless the new building is an ultra-low-carbon design. Even then, when considering near-term and long-term climate targets (2030 and 2050), retrofit could still outperform these low-carbon options. If a new building is preferred, projects should consider mass timber or other low-embodied-carbon materials and propose end-of-life scenarios that would reuse the wood without releasing its carbon back into the atmosphere.

Several limitations and assumptions are inherent in wbLCA and in this study. Nevertheless, results show that retrofitting office buildings and preserving the embodied carbon emissions in a structure can help achieve Canada’s climate targets and net-zero goals.

More LCA case studies would help to expand the findings of this research to other regions and types of buildings. Further, more standards and guidance on modelling carbon emissions from the later stages of product and building lifetimes is required and would help the commercial real estate industry make carbon-informed decisions about retrofit versus demolition and new construction.

Below are the main takeaways from this study:

1. Deep green retrofits achieve the same post-construction level of annual operating carbon emissions as demolition and new construction. Deep green retrofits also result in lower whole-life carbon emissions due to the savings from not rebuilding the structural system.
2. The case for retrofits is strongest in regions with green electricity, such as British Columbia, Quebec, Manitoba, and Ontario.
3. If new construction is required, it is beneficial to limit embodied carbon emissions by focusing on low-embodied-carbon materials, including low-carbon concrete and steel, and bio-based materials such as wood. Accounting for biogenic carbon storage in biomass materials can also support the case for building new timber buildings, since it can lead to similar whole-life carbon as retrofits. More analysis for calculating biogenic carbon is required.
4. Additional guidance and data are needed to link circularity and reuse principles to embodied carbon emissions and LCA benefits.

---

Related Publications

Opportunities to Apply Circular Strategies to Existing Office Buildings