By Adam Auer
When it comes to strategies for addressing climate change, it is unsurprising buildings are taking centre stage. Globally, the construction, operation, and decommissioning of buildings and infrastructure account for approximately 40 per cent of all anthropogenic greenhouse gas (GHG) emissions. Three-quarters of these emissions are associated with the operation (heating, cooling, lighting, etc.) of existing buildings, while the remaining 25 per cent is attributed to ‘upfront,’ embodied emissions associated with manufacturing of building materials as well as emissions from construction and maintenance.
Until recently, the predominant focus of addressing the climate impacts of buildings has been to improve operational energy efficiency, largely because these emissions have made up the lion’s share of a facility’s GHG emissions over its full life cycle. Driven in part by advances in operational efficiency as well as the coming of age of life-cycle assessment data analysis and tools, the embodied emissions of building materials have now come under scrutiny.
The emerging interest in embodied emissions has put concrete in the spotlight as:
- the most common building material (by weight, twice as much concrete is used globally than all other materials combined); and
- it has a significant carbon footprint.
This raises important questions. What role does/could concrete play in decarbonizing the built environment? Can concrete compare favourably to other building materials in a net-zero carbon world? What does concrete’s path to carbon neutrality look like?
Heating, cooling, and powering buildings
For years, the drive toward climate-friendly buildings has been fixated on tighter and better insulated building envelopes to reduce heating and cooling energy loads. Operational efficiency is of particular importance in temperate regions like Canada where operational energy demand can drive over 90 per cent of a building’s GHG emissions over its lifespan, and doubly important where electricity is generated using GHG-intensive fossil sources like coal.
As our ability and willingness to reduce the heating and cooling demands of facilities improve, so, too, does the potential for net-zero building operations. Whereas ‘electrification’ and low-carbon sources like hydrogen were once GHG-mitigation strategies confined to the auto sector, they are now also seen as a viable pathway for net-zero buildings operations.
When it comes to operational emissions from buildings, concrete can have a significant impact. The material’s natural imperviousness to air and water can help achieve a tight building envelope. Arguably, concrete’s most important property when it comes to reducing operational GHG emissions is its thermal mass. Studies suggest strategic integration of thermal mass into a building’s energy management system can help reduce as well as shift heating and cooling loads and lead to significantly less GHGs as well as operational costs (see “The Thermal Mass Advantage”).
Thermal mass can also drive climate resilience or what some call “passive survivability” by leveraging a building’s structural concrete as a giant thermal battery, enhancing the building’s ability to maintain critical life-support conditions if services such as power and heating fuel are lost in extreme heat or cold.
Without abandoning a commitment to pushing the boundaries of operational efficiency, leading voices in the architectural and developer community are turning their attention to the other significant source of GHG emissions from construction—in particular, those associated with building materials.
Together, the production of the two most common structural materials—steel and concrete—are estimated to account for more than 11 per cent of global GHG emissions. If this number is contextualized at the building scale, its significance is more obvious. Of all the embodied emissions in a typical multistorey building, close to 50 per cent can be attributed to the concrete used in the building’s structural elements.
This has led some to look for alternatives (e.g. wood), but only to find that cutting embodied carbon is not straightforward and there are no silver bullets (see “Mind the Carbon Gap”).