Welcome back! Building on Aspect Climate Chronicles Part 1, we’ll now get into how carbon is accounted for and some of the ways that we can design for a reduced carbon footprint.

How is Embodied Carbon Calculated?

There are several ways to calculate the embodied carbon of a structure or building. You can use a standalone Whole Building Life Cycle Assessment software, a plugin software as part of a 3D modelling platform, a pre-existing tool, or you can develop your own.

For maximum flexibility and relevancy, we chose to develop our own in-house tool. This is based on the IStructE guide to calculating embodied carbon, adapted for Canadian values, and specific to the structural elements.

We anticipate (and hope) that over time this tool will become obsolete as industry standards become increasingly common, but in the interim we’ve found that the flexibility of our own tool allows the most relevant, up-to-date and accurate data to inform our decisions.

The calculations are in essence very simple: volumes or weights of all the structural materials are obtained through building 3D virtual models or manual take-offs from drawings. These quantities are used to determine Global Warming Potential (GWP) for modules A1-A3, A4 and A5 (Production, Transport to Site and Construction respectively).

With these results we can compare schemes using different materials or structural layouts, identify where savings can be made, produce reports for architects, clients or contractors and begin to educate and understand how our building designs are performing.

Sample Summary page from Aspect’s Embodied Carbon Calculation report.

What are some of the key changes we can make to the design of a building to help reduce embodied carbon? 

Refurbish!

Refurbishing an existing building has a considerably better carbon footprint than demolishing and replacing it. While certainly not suitable in all circumstances, refurbishment requires a creative and forward thinking team, willing to work within the constraints that an existing building inevitably provides. Renovation usually comes with more unknowns and is often the harder path to take. Our role as structural engineers puts us in a unique position to assess ‘the potential’ of existing building stock and influence these types of decisions. There are a host of tools in our tool belt to help bring adaptive reuse projects to life. We need to be open to ideas, and clearly represent the unknowns and risks to our teams.

Design appropriate, rational buildings

Unnecessary complexities in design lead to complicated structural arrangements which can increase material takeoffs, and in turn, embodied carbon. Limiting changes to a structural grid about the height of a building can make a significant impact – transfer slabs take note!

Efficient, well-designed structures are one of the best ways to reduce carbon (and costs!). By bringing structural engineers on early in the design, at the massing stage, we’re in a position to at least comment on efficient structural strategies, while also layering in embodied carbon considerations. While it would be fun, by no means are we trying to play architect here, but small tweaks early on can result in massive carbon (and cost) savings later on.

Graphic above from the IStructE Guide Design for zero 

Use the Correct Materials for the Application

The energy used to process timber into a structural element is generally significantly less than a corresponding concrete or steel member, by volume. This does not however mean that timber is the best solution across the board.

Long spanning structures may be more efficient in steel than in timber, and thin pre-stressed concrete slabs may sometimes be more appropriate than thick mass timber panels with extra beams and columns. Sometimes fire rating requires an excessive sacrificial charring layer of mass timber and a thin concrete element will be more efficient in cost and carbon.

Location can have a significant impact too: remote sites produce much larger transport emissions, making lightweight construction favorable. Heavy structure in high seismic regions can dramatically increase lateral loading, causing trickle-down effects to bracing and foundations. All of these factors should be considered!

Design for Longevity

The longer a building is around the lower the relative impact of constructing it, and the less we need to build over time. A building that is demolished and rebuilt every 20 years with modern technologies and materials is far worse from a carbon standpoint than a building that is built to last for 100 years. We need to design with flexibility and with resiliency (seismic and climate) in mind. The world is ever changing, but projected changes in use, temperature, precipitation and wind can reasonably be accounted for today. Structures that self-center and that can be readily repaired (and not demo’d) after earthquakes can happen now too.

Design for Circular Economy

Designing a building to be disassembled and reused has legs. This approach allows a member (or assembly) to be repurposed as structure or raw material in a future building. While simple in concept, particular attention should be taken when contemplating more ‘permanent’ structural strategies. Examples of permanence include conventional concrete buildings, steel or timber concrete composites, or the installation of a multitude of smaller diameter fasteners that will pose a challenge to eventual remilling or visual appearance.

As low hanging fruit, connections can easily be made with bolts and screws as opposed to welds and glue.

In a time of seemingly ever changing code requirements, there are intricacies in how to properly document and instruct the professionals ‘of the future’ who’ll be repurposing these elements, but strides are being made.

A temporary sales center for Bosa Properties comprised of locally sourced CLT panels over glulam beams. Care was taken in the design of the structure to allow it to be removed and re-assembled for future use. Architect: Leckie Studio; Photography: Ema Peter 

Reduce the Use of Concrete or use Cement Alternatives

Cement production alone accounts for approximately 8% of global carbon dioxide emissions. Reducing concrete, and more notably cement, will help significantly lower carbon in buildings. Buildings tend to have large underground elements (parkades) and foundations that will remain concrete for the foreseeable future. When foundations and substructures cannot be designed away or reduced, or where alternative low carbon materials are not suitable in the superstructure, the use of cement alternatives should happen today.

Right now there are easy, simple, and cost-neutral (or cost-effective) solutions that can make small to moderate, but still meaningful reductions. There are also larger moves that can be made to use concrete mixes with significantly reduced embodied carbon.

As we don’t tend to put a direct and appropriate price on carbon, these moves can tend more costly, with effects on the construction process needing consideration. In some locations, concrete manufacturers are developing “Net Zero” concrete which involves the direct air capture of carbon dioxide produced from manufacturing. Though promising, this technology remains niche and likely a few years away from mass adoption.

Graphic from the Government of Canada Publication Strategies for low carbon concrete 

Further information on calculating embodied carbon and Whole Building Life Cycle Assessments can be found at the following resources:

Government of Canada: National guidelines for whole-building life cycle assessment

IStructE: How to calculate embodied carbon (second edition)

Stay tuned for Part 3!