In coming years, we need to change how we design our buildings – specifically, to start assessing and reducing the building carbon footprint. MBIE has proposed making this mandatory within the Building Code. Such assessments are conducted using building carbon footprinting tools – software that simplifies the otherwise complex process. BRANZ has been conducting research into how these tools can better meet the needs of the industry.
What is a carbon footprinting tool?
A carbon footprinting tool (CFT) is software that can help project teams calculate the carbon footprint of their building designs so they can make informed lower-carbon design decisions. Generally, a user will need to input what resources (materials, energy and water) the building is estimated to use, and the tool will calculate the carbon footprint of those resources.
CFTs can be different from each other – some are web-based while others are Excel-based, some simplify inputs at the expense of flexibility and some assess other characteristics as well such as cost and energy efficiency. However, most tools are intended to be used throughout the entire design process – particularly during early design as this is where there is the most potential to test lower-carbon design decisions.
Understanding industry needs
As part of BRANZ’s research, stakeholders were brought together to discuss what the building industry needs from a CFT (see BRANZ Study Report SR473 Roadmap for evaluating building performance for low-carbon houses). We then compared several CFTs available in the Aotearoa New Zealand market to what was found during these discussions.
All the tools we looked at made carbon footprinting significantly more accessible and will be important for helping the building industry transition to low-carbon buildings. However, there were some aspects that arose out of the stakeholder discussions that aren’t currently being met by CFTs. These can serve to highlight key areas for future development to help on our journey to a net-zero carbon future.
A single source of truth
The CFTs we investigated use different underlying data and assumptions. Carbon footprinting is a data-intensive process requiring the assessor to use multiple data points and consider many defaults and assumptions for one design. A benefit of these tools is that they help users make well-informed assumptions and contain comprehensive environmental data so they don’t need to source these datasets themselves. However, since these tools use different data and assumptions, they can calculate different carbon footprints for the same design.
These differences become significant when they are great enough to change the design decision a project team makes. This can lead to a building having a much higher carbon footprint if that design decision affects a significant component in the building such as the structure or thermal envelope. When compared to each other, these tools also currently lack the consistency needed to calculate a carbon footprint for building consents.
One solution is to make a single source of data that all CFTs draw from. Essentially, Aotearoa would establish a database that contains data, defaults and assumptions needed to carbon footprint buildings. Each tool could then query this database when undertaking a carbon footprint assessment. This would mean that building carbon footprints should be more consistent regardless of what tool a project team decides to use. Criteria would need to be developed to test CFTs to ensure they calculate building carbon footprint results to within an acceptable range. It would also mean that consent officials won’t need to investigate the underlying data when assessing a consent application, saving time and cost.
Harmony with other evaluation criteria
Within these tools, other metrics that the industry considers important were not considered holistically. Buildings need to fulfil a range of functions – to provide safe and resilient shelter from the elements, that is healthy and comfortable and has minimal impact on the environment – and all delivered at an acceptable cost. We usually model how a building will perform these functions, often early in design, so that we can test the impact of early design decisions before they are locked in. This is a critical part of delivering safe, comfortable and environmentally sustainable buildings.
Currently, how well a building performs these functions is considered separately, if at all. It is also common for one function to be prioritised over others, depending on the project brief. This means that the design may perform well in one area while potentially performing poorly in another. The tools we investigated as part of our research often only considered the building’s impact on the environment, ignoring other important considerations.
A better way to design would be to assess a building’s ability to perform these functions in a holistic manner. This would enable us to better consider these functions early in the design process and ultimately deliver better-performing buildings. It would also allow us to balance how well a building performs these functions so that it doesn’t fail to perform one of the functions it needs to. The introduction of carbon footprinting into the design process and the uptake of CFTs is an excellent opportunity for us to start working towards taking a more holistic approach to design, supported by tools that assess a building’s ability to perform multiple functions.
Knowing what data to use
The CFTs we assessed as part of this research require users to assign environmental data to the materials within the design. In an ideal scenario, there is environmental data for the specific product that is being specified so that the assessor just needs to pick the correct product. However, there is a lack of data available for the products that are often used here, and it is best to start carbon footprinting a building during early design before specific products have even been decided.
This means that an assessor needs to pick a dataset that best represents the product that they are potentially going to use. This can be difficult as the assessor needs to have a good understanding of the products they are using such as knowing how they are manufactured, which is often beyond the level of understanding they would normally have. They would then need to have this level of understanding for the potentially hundreds of products that the design will use.
This can lead to assessors not picking the most appropriate dataset available – ultimately degrading the quality of the assessment and potentially leading to poorly informed design decisions. There is also a risk that assessors may pick a dataset with the lowest carbon footprint rather than what best represents the product proposed for use in the building, leading to the building’s greenhouse gas emissions being higher than what is calculated.
This is a complex issue as it requires change in a range of areas. There needs to be more environmental data available for products used in Aotearoa, there needs to be better guidance on how to deal with unknowns when calculating a building carbon footprint and project teams need to develop a better understanding of the products that they’re putting into their buildings. However, CFTs have the potential to contribute to addressing this issue by simplifying what information they ask users to provide and providing guidance on what data to use.
Conclusions
Ultimately, this research showed that CFTs still have a few challenges to face if they are going to help the built environment deliver lower-carbon buildings and demonstrate compliance with MBIE’s proposed changes to the Building Code. These issues cannot be addressed by tool developers simply updating their tools as they are system wide. Instead, there needs to be greater collaboration between government and industry to provide the technical infrastructure and guidance needed so that these tools can be used properly and in a consistent manner.