The Role of the Structural Engineer in Sustainable Design

essex centre of research hallway interior. wood accents and large bright windows
Essex Centre of Research (CORe) University of Windsor, ON Structural Design by NORR Photo Credit: doublespace photography

At NORR, our engineering team across the globe works collaboratively to share knowledge about structural design solutions that are resilient and help clients to meet specific carbon emission targets.

Today, carbon dioxide levels in our atmosphere are considerably higher than they have been in the past 800,000 years. Per the IEA/UN Global Status Report for Buildings and Construction 2019, the building and construction sector contributes 11% of the entire CO2 emissions worldwide, a number that needs to improve. As architects and engineers, we have a responsibility to our local and global communities to reduce the impact of designs we are entrusted with, whether new or renovations.

Much is done to save on buildings’ operational energy; however, Architecture 2030 estimates that embodied carbon emissions of new constructions over the next 30 years, will be equivalent to operational carbon emissions over the same period. Embodied carbon is that emission associated with the extraction of raw construction materials and therefore their fabrication, transportation, erection and finally deconstruction at the end of life. In other words, about half of the carbon emissions would have already taken place by the time the building is commissioned and occupied. The design decisions that structural engineer is a party to grossly influence the magnitude of a building’s lifetime carbon emissions.

How can we reduce the impact on the carbon footprint? 

There are several avenues to explore to reduce embodied carbon. It starts with the endeavor to reuse building stocks instead of constructing new ones. Whether it is a new built or a renovation, however, architects and engineers should strive to limit the use of carbon-intensive materials, choose carbon sequestering alternatives, specify low-carbon concrete mixes and use high-recycled content materials. Even the good practice of maximizing structural efficiency results in the reduction of embodied carbon.

Canada is to mandate the reduction of cement clinker, the most intensive concrete ingredient in CO2 emission, by 10% in all federal construction mainly through the use of limestone Portland cement, as I had blogged in June 2020. This, and more, can be achieved through better mix design, use of pozzolanic cement substitutes and better yet through performance specifying concrete mixes that have limits on their carbon emissions. Just as we regularly specify concrete strength without getting into mix design, one can specify a value of xxx kgCO2/kg of concrete for a specific concrete strength.

Is there a material we should be giving more consideration to?

Concrete and steel advocates make the case for how these materials can be applied in an environmentally responsible manner. Many such arguments are valid and deserve careful consideration. Life cycle analysis (LCA) of carbon emission will provide a cradle-to-cradle understanding that will guide designers and property owners alike as they make the important choices of selection of materials and systems. There however has been an exceptional excitement about Wood as the most environmentally friendly construction material. As engineers, we are convinced by numbers and there is one number that is striking when comparing wood to say steel. The production of 1 kg of steel, even while allowing for the typical recycled content, results in the emission of about 1.8 kg of CO2. Curiously and coincidentally the production of wood, which is the growth of a tree, entails capturing and storing this same amount of 1.8 kg of CO2 for every 1 kg of construction timber. Of course, for this advantage to hold, it is to be assumed that this wood comes from replenishable trees that are FSC (Forest Stewardship Council) certified and that the wood at the end of the building’s life will be recycled rather being incinerated or buried in a landfill. NORR is currently working with Public Services and Procurement Canada on the design of a pioneering multi-story wood construction federal building in Ottawa that is to be a flagship for such environmentally responsible project in the capital region.

How are structural engineers at NORR helping? 

NORR’s stated mission, in part, is the pursuit of a socially aware, environmentally responsible and financially viable architecture and engineering design solutions. Our mandate to achieving that is to understand the issues involved, fine-tune the design and document the LCA of embodied carbon in every new construction and rehabilitation project. That can only be successfully done in partnership between the architect, engineer, LEED® consultant, client and other stakeholders.

Hassan Saffarini,Principal