A Life-Cycle Assessment of a Retrofit

By Elisabeth Baudinaud

Many homes—including many that are far from the end of their operational lifespans—are demolished each year to make space for new construction projects. The embodied emissions from the materials used to build those homes are significant but rarely accounted for when considering the operational emissions savings. If the end result of those projects is a building that meets the needs of the same number of individuals, offering only improvements in comfort or operational energy efficiency, then the question is worth exploring of whether those same goals could have been achieved by renovating the existing building, at a significant savings of embodied emissions.

This question is one that we at Carbon Wise, a firm based in Vancouver, British Columbia, were brought in to address by homeowners who were contemplating a major renovation. The intention behind the renovation was to improve the energy efficiency of the home to meet the Canadian Home Builders’ Association net-zero standard (CHBA-NZ or NZ). The homeowners were sensitive not only to the operational emissions of their home but also to the embodied emissions from the materials that would be used to accomplish the net-zero renovation. To address the homeowners’ questions, we conducted life cycle assessments (LCAs) of their project.

Our LCA included the deconstruction (C2-4) of the original building, and the production and construction (A1 to A3) of the retrofitted home, including photovoltaic (PV) systems necessary for net-zero operation. Carbon Wise compared those results with an LCA of a business-as-usual scenario in which the original home would have been demolished and the new home built from entirely new materials.

The building is a one-story detached home in North Vancouver, BC that is 2,960 square feet with a basement. It was originally built in 1958 using 2X4 wood frame construction, with an attic truss roof, on an unfinished concrete basement. The new home design included upgrades to a 2x6 exterior wall and a new roof design incorporating scissor truss construction and a section of flat roof. Additional floor space was added to the above-grade floor as an exposed floor area. The basement geometry was unaltered with some minimal additional material added to suit the new layout above and changes in rough openings. New framing and insulation were added to the below-grade structure.

The scope of the LCA included all of the major structural, enclosure, and partition materials (foundations, walls, floors, roofs, windows, and cladding materials) and photovoltaic systems. This represents the majority of the mass of materials in a building project. The LCA’s product stage—modules A1-A3—were modeled using BEAM/MCE2. The use stage, consisting of module B6, was modeled using Canada’s HOT2000 energy model. The end-of-life stage, modules C2-4, was based on data from Unbuilders.

Module D is composed of two sets of data. One is a calculation of the materials reused in the renovated home, that would have otherwise been constructed of similar new materials. The second is estimated based on the most recent data from RMI, CLF estimating the reuptake of recycled materials salvaged from the original home. To account for the savings associated with reuse and retrofit, the environmental impacts of the retained materials are excluded from Module A in the retrofit LCA, but included in Module D.

Reuse and Storage (Module D)

Reuse of materials and carbon storage are aspects of an LCA that are not as fully defined in terms of what data is to be included and how it is to be treated. This has become an ongoing conversation among professionals working in whole-building impact assessment and cannot be fully addressed here, but the question of the reuse of materials on and off-site is relevant to this case study.

Salvaging materials for potential later use rather than sending them to landfill represents a savings of energy, and also avoids the emissions of methane and other GHGs that materials emit as they decompose in the landfills. Therefore, salvaging for reuse is a practice that should be lauded and practiced as widely as possible. However, the calculation of the energy and carbon savings is difficult. Do the savings of those impacts apply to the building they were removed from, the one they are reinstalled in, or both?

On the other hand, materials that are left in place and integrated into the structure of a new building on the same site avoid many of these uncertainties, and lend themselves to being calculated in terms of their direct equivalencies to the new materials that do not need to be produced from virgin sources. For this reason, it was determined that materials falling into these two categories would be treated separately.

Comparing the Scenarios

The following scenarios were evaluated for this case study.

Baseline – The existing home was evaluated and energy modeled according to EnerGuide procedures, and this model was used to establish a pre-renovation baseline for operational energy use.

Scenario 1 - New build: A new home is built using conventional practices with the intent to reach CHBA net-zero or net-zero ready standards. Embodied and operational modeling reflect a situation where the original home has been fully demolished, with the assumption that all demolition waste was sent to the landfill and all construction utilized new materials.

• Scenario 1a, explores the home without the installation of PV systems (net-zero ready).

• Scenario 1b, explores the home built with a PV system to reach CHBA NZ.

Scenario 2 - Deep Energy Retrofit: The home is selectively deconstructed by Unbuilders; some of the materials are recovered and repurposed. The home undergoes a deep retrofit with the intent to reach the CHBA NZ standard, with an emphasis on retaining as much of the existing material and structure of the building as possible. Embodied and operational modeling reflect this situation. Any material that could reasonably be reused in place was calculated separately and considered as stored energy. The remaining material volumes were considered new material and calculated accordingly using the best available impact data. Operational energy modeling reflected the home constructed under these conditions.

• Scenario 2a explores the base house without the installation of a PV system (net-zero ready).

• Scenario 2b includes the addition of a PV system to reach CHBA NZ.

Figure 1 compares the operational emissions over time of the baseline home compared to the four scenarios. The home’s pre-renovation operational emissions of 8.2 tonnes of CO2e per year were available from a pre-retrofit EnerGuide Evaluation. Because the building was originally constructed in 1958, for this comparison the embodied emissions were taken to be zero at this point in time. We can see the time required to achieve a net savings of CO2e as a result of undertaking a new or a reconstruction project. This is the time at which the cumulative emissions savings of the renovation or the reconstruction of the home would equal the upfront investment of emissions associated with construction.

In the case of a new build, the timeline for this was almost exactly 4.4 years, or 4.9 years when embodied emissions from solar panels were included in the net-zero scenario. In either renovation scenario, the payback time was shorter still, equaling 3.5 years or 4 years in the net zero variation.

This demonstrates the value of addressing operational energy efficiency in older homes. A house that has high annual energy consumption very quickly emits enough operational CO2e to equal the embodied CO2e of either renovating the building to a much higher level of energy efficiency or replacing it altogether with a new build.

However, that does not necessarily mean that both renovation and reconstruction options are equal. When the total emissions equivalent options are compared across these scenarios, the embodied emissions were 7.9 tonnes CO2e lower—roughly comparable to the emissions from driving a gas car for more than 32,000 kilometers (20,000 miles)—when the home was partially deconstructed and renovated, as compared to demolishing and building new, due to the reused components (see Figure 2). This difference amounts to a total embodied emissions reduction of 19.3% when compared to the same home with all new materials and 21.8% if a PV system is added to the design.

Material Substitutions

When any form of whole-building life cycle analysis is conducted, particularly during the design phase of a project, it is relatively easy to consider material selections and substitutions early, and with as much information as possible on what materials contribute the largest impacts. In this case study, three materials were top impactors across all scenarios: the metal roofing, the vinyl-framed, triple-glazed windows, and the fiberglass insulation in the attic. Figure 3 shows the impact of substituting these materials for similarly performing alternatives with lower impacts. It quickly becomes apparent how some simple decisions made early on in the design process can reduce the embodied carbon associated with the building. 

Conclusions

These data support the conclusion that a deep energy retrofit provides many opportunities to lower a building’s embodied emissions when compared to building a completely new structure, while arriving at essentially the same energy efficiency and comfort levels. The careful selection of low-carbon building materials remains an essential factor in ensuring these benefits are fully realized. The Material Emissions Benchmark Report for Part 9 Homes in Vancouver concluded that average net emissions from a home in the City of Vancouver amount to 43t CO2e with an average emissions intensity of 193 kgCO2e/m². Our study demonstrates that a deep energy retrofit, particularly one using carefully selected low-carbon materials can result in significantly below-average embodied emissions of 120 kgCO2e/m².

—Elisabeth Baudinaud is the founder and principal of Carbon Wise.

More details about this case study can be found in the Carbon Wise LCA Case Study Final Report.