What actually drives lower embodied carbon in high-rise buildings?

In February’s post, we reviewed a dataset of 26 projects issued for construction in 2025 and one particular project stood out. Not because it used new materials or unconventional systems, but because of how deliberately it was refined.

Across the dataset, three strategies consistently led to lower embodied carbon intensity (ECI):
1. Minimize basement volumes
2. Remove Building Transfers
3. Optimize the building height/stiffness

This project performed strongly across all three and achieved the lowest ECI in the group – look for the green dot in the chart below.

(ECI vs building height. The size of each point relates to the floor area of the building.)

What is ECI and why does it matter?

For those less familiar with the terminology of building sustainability (yes, there are lots of acronyms), ECI is the metric we use to measure the greenhouse gas emissions associated with the construction materials used in a building. We normalize the ECI metric per square meter of floor area so projects of different sizes can be compared more effectively.

Ultimately, we want to minimize any greenhouse gas emissions as they contribute to climate change.

Project overview

The structure-only ECI was estimated to be 252 kgCO₂e/m², the lowest of all 26 projects, and significantly below the typical 300-500 that we regularly see for high-rise concrete structures in BC.
This hotel project sits in the heart of downtown Vancouver. The structure has 4 below-grade levels and the roof slab is 100m above grade at L32. For any engineers who are curious, the building has flat-plate reinforced-concrete floors and is designed with ductile shear walls and ductile coupled walls. The site class is B, Sa(0.2) = 0.839, PGA is 0.364, and the seismic design is under the NBCC 2015 provisions.

Basement size: Managing what doesn’t count (but still matters)

Basements are one of the most significant and often overlooked drivers of embodied carbon.

Building large parkades and extensive exterior areas increase the building ECI. This is partly due to the intensity of materials used to build underground or heavily landscaped areas, but mostly because of the nuance of the ECI calculation metric, which excludes the floor areas of these elements in the calculation while still including the material embodied carbon. This calculation methodology promotes transit-friendly developments and less reliance on vehicle infrastructure and travel, an admirable parallel strategy for reducing global greenhouse gas emissions.

 

Due to the usage of this building and the massing, the basement structure is relatively small, and the building maximizes its floorplate within the plot. This project could provide up to 195 stalls within the permitting requirements. However, due to the usage considerations and other discussions within the development team, 42 parking stalls have been provided. To put this in perspective, doubling this parking count would require three additional parking floors below grade, and likely increase the ECI by over 30%

It is very important that projects consider appropriate parking strategies in their building. Being a hotel downtown near bus routes, it is expected that most occupants will take transit to this area, and so it is appropriate to minimize the parking provision.

Building transfers: aligning structure with architecture

We were fortunate to be able to work closely with the architecture and wider project team to effectively remove transfers from this project. We used a strategy of stepping the columns gradually from their position in the tower floorplate to the parking layout below. These columns were only offset by approximately 0.3 to 0.9m, and so it was much more efficient to build larger columns than to provide an exhaustive layout of deep transfer beams at L1.

This is expected to reduce the ECI by about 5-25 kgCO₂e/m² compared to other comparable projects.

Optimizing the LFRS design: designing to the limit and not beyond it

In our February OnTrack post, we identified that buildings between 25 and 35 stories often have efficient Lateral Force Resistance Systems (LFRS). These are the elements that resist the earthquakes, windstorms, or any other horizontal force or acceleration imposed on the building. There are two main streams of designs for the LFRS:

• Strength – ensure the building is stable and strong enough to resist the horizontal loads
• Stiffness – ensure the building sways within the required drift limits. This can be for occupant comfort, to make sure secondary components are not damaged, or to remain within property lines and setback limits.

This project was challenging as the floor plate was very close to the adjacent property, and the drift limits were strict to ensure the building does not cross the property line in an earthquake event (which could cause the buildings to collide).

The project has an additional elevator bay outside of the circulation core that feeds the full tower height. Although it is tempting to use that additional circulation core to add to the LFRS, the additional stiffness results in significantly more force being attracted during an earthquake event, which creates some inefficiency in the amount of material required in the LFRS and also requires the foundation to be much larger. What we focused on was sharpening the pencil in the analysis models and design so that only the primary circulation core constituted the LFRS. We designed this building right to the drift limits and leveraged all of our expertise and skill in developing and running analyses to ensure this building met the design limits with the minimum amount of structure required.

This is expected to reduce the ECI by about 15-40 kgCO₂e/m² compared to other comparable projects.

Efficiency-Driven Design with Measurable Carbon Reduction

This project is a strong example of how targeted structural refinement can produce a lower-carbon building. In addition to reducing material volumes, we specified 56- and 91-day concrete mixes, allowing for lower cement content and further reductions in carbon intensity.

By minimizing below-grade volume, aligning the structure to eliminate transfers, and optimizing the lateral system to meet—but not exceed—performance requirements, the team achieved:

• Approximately 25% lower embodied carbon
• Up to 40–50% reduction compared to more car-centric developments
• Estimated cost savings of $680,000

The result is a structure that performs efficiently—both environmentally and economically—without relying on new materials or unconventional systems.

Written by Rory Roberts, P Eng

Together, we can contribute to a more sustainable built environment. If you are interested in sustainability and would like to discuss any of the topics in this article, please get in touch with us at [email protected].

For more information on our sustainability initiatives and to stay updated on our latest projects, visit our website and follow our OnTrack blog series.