With operational emissions minimized through an all-electric design—featuring heat pumps, HRV systems, and no reliance on natural gas—the focus on embodied emissions becomes even more critical.

As the building’s energy use becomes cleaner, the proportion of carbon emissions stemming from the materials and construction process gains greater significance. By conducting a Life Cycle Assessment, the team incorporated several strategies. These included optimizing structural efficiency using low-carbon materials where feasible and minimizing waste during the construction of modular and prefabricated walls. These not only lower the overall carbon footprint but also often result in cost savings through reduced material usage and more efficient construction processes.

Additionally, prioritizing embodied carbon reduction encouraged innovative design solutions, such as relocating the staircase outside, which decreases the need for internal space and reduces the total floor area. Addressing embodied carbon is therefore essential to ensure a holistic approach to sustainability that covers the full life cycle of the building.

The key strategies include the following:

• No parking/basement and use of low-carbon concrete on foundation

Proposing only three parking spaces at street level decreases the amount of concrete and steel required for parking structures. Based on past projects, this could result in an estimated savings of 250 tons of CO₂e. While parking was not factored into any of the scenarios in this case study, it is still worth highlighting as a significant potential contribution to reducing the overall carbon footprint. Parking areas often involve significant material use and energy-intensive construction processes, contributing significantly to embodied carbon. By limiting the number of parking spaces, the overall demand for these high-carbon materials is reduced. Plenty of bike storage has been implemented to balance the lack of parking.

Where concrete was necessary for the design, the team opted for a low-carbon alternative that incorporates 40% supplementary cementitious materials (SCM).

• Simple wall and roof assemblies

Simple wall and roof assemblies reduce embodied emissions on this project by minimizing material use and waste, streamlining production, and facilitating easier transport and handling. Additionally, their straightforward design often leads to quicker and more efficient construction, further reducing emissions associated with labour and machinery. Simplified assemblies also tend to be more durable and easier to disassemble to allow for future upcycling or reuse, supporting a more sustainable end-of-life scenario for the building materials. If a whole-building life cycle assessment (WB-LCA) was completed for this project, such that the embodied carbon of the end-of-life stages (i.e., C1-C4), and the beyond-building life (i.e., life cycle stage D) were measured, it is reasonable to assume that even greater embodied carbon reductions could be realized on this project.

Switching from a standard 2x8 mineral wool batt assembly using the industry average to a 2x8 wall filled with dense-pack cellulose sourced from local wood suppliers can reduce the project's carbon impact from 11,152 kgCO₂e to -4,309 kgCO₂e. This transforms the wall assembly into a carbon-storing solution. Likewise, replacing a standard TJI roof of fibreglass batts with a dense-packed cellulose roof using locally sourced plywood reduces the project's carbon footprint from 17,734 kgCO₂e to 4,368 kgCO₂e.

It's important to mention that the vinyl roof tile chosen for this project was approximated using a similar option from the database (refer to the methodology section). While it shows a higher upfront impact, the manufacturer offers a warranty of up to 50 years compared to the 15-to-20-year replacement cycle typical for asphalt shingles. Due to limitations of the BEAM software, a full life cycle comparison could not be conducted for this material.

• Small suites, efficient spaces

Simpler unit designs (all units are rectangular) often involve standard components that are easier and more energy-efficient to produce, transport, and assemble. By reducing complexity and focusing on efficient use of space, small and practical unit layouts contribute to a lower embodied carbon footprint while maintaining functionality and comfort. The proposed flex residential units feature a versatile design with a bedroom that can be seamlessly shared with an adjacent unit, enhancing adaptability and functionality. The core concept revolves around a modular bedroom space that can be opened or closed to connect with the neighbouring unit based on need. While it's difficult to quantify these savings in the LCA, it's important to consider the potential benefits of reducing material use altogether; the savings come from what is not included in the first place.

• Low form-factor massing (rectangular design)

The building's simple shape maximizes available interior space relative to the area of its envelope and so requires fewer materials compared to a complex, irregular design. Fewer materials mean less extraction, processing, and transportation, which effectively reduces embodied emissions and supports better operational efficiency.

Although difficult to quantify specifically, simple form factors lend themselves to efficient construction timelines and easy access during construction. They can encourage engineers to optimize material considerations in structural design by allowing flexibility when considering the distribution of load over required spans. They facilitate efficiently designed HVAC systems that distribute air more evenly and support lower operational energy consumption while also reducing required ducting equipment.

• One interior, one exterior staircase

One strategy used to simplify the building's design entailed relocating one of the stairs to the exterior of the building, effectively reducing the need to free internal space for residential use and simplifying structural and mechanical design.

An exterior staircase can reduce the area of internal walls and floors required for a similar internal staircase. This, in turn, decreases the total amount of envelope materials (such as drywall, insulation, and finishing materials) needed for the building. The exterior staircase also simplifies the interior layout, reducing complexity in the construction of internal partitions.

• Composite cladding and stucco

One of the selected cladding materials is composite cladding, which is often made from recycled or low-carbon-content components. This typically requires fewer resources and energy to produce and install compared to conventional options. The other system selected is stucco (industry average option in BEAM), which is durable and weatherproof in a single, streamlined system that reduces the need for additional layers and materials. The materials used in stucco—sand, cement, and lime—are typically sourced locally. This reduces transportation emissions and supports local economies. The proposed long-lasting materials will extend the lifespan of the building envelope, minimizing the need for frequent replacements and repairs. Foam products are not used above grade.

• Cellulose and hemp batt insulation

The use of cellulose and hemp batt insulations will help minimize embodied carbon in the building by incorporating renewable, low-carbon materials. Cellulose, which will be used in exterior wall and roof assemblies, is a cost-effective and sustainable choice. Not only does it reduce the carbon footprint of these assemblies, but it also supports a circular economy by utilizing recycled materials. Hemp batt insulation will be applied in non-fire-rated interior walls, such as suite divisions, offering another rapidly renewable option that requires less energy and fewer resources to produce than traditional insulation. This approach, providing both environmental and financial benefits, might be one of the simplest solutions to implement to reduce embodied carbon.

• GPS insulation under slab reduced (No foam products over slab)

By optimizing and reducing the thickness and application of below-slab insulation, the overall embodied carbon will be reduced. Reducing reliance on excessive insulation can lower the total material requirements, further decreasing the carbon footprint associated with the building's construction. In this case, XPS rigid foam insulation was used for comparison; by minimizing the insulation where it's not needed, we can significantly reduce both material usage and environmental impact without compromising the energy performance and thermal breaks.

• Fibreglass windows

The production of fibreglass involves melting glass and combining it with resins at high temperatures, which is an energy-intensive process that results in higher initial carbon emissions. However, despite their higher upfront carbon impact compared to vinyl or wood windows, fibreglass windows offer a balanced, resilient, and long-term choice. Their exceptional durability, energy efficiency, and low maintenance over a lifespan of up to 50 years is significantly longer than the 15-20 years typical for vinyl or wood. Their durability and low maintenance result in a longer lifespan, reducing the need for frequent replacements or repairs. While the initial embodied carbon may be higher, a full cradle-to-grave whole-building Life Cycle Assessment might justify the extra investment compared to vinyl or wood.

The decision to use double-pane windows over triple-pane was a conscious choice aimed at reducing embodied carbon, as double-pane windows typically require fewer materials and resources during production. Double-pane windows often result in cost savings, both in terms of upfront purchase and installation, while still providing the required thermal performance for energy efficiency.