‘Three point estimating’ will be a phrase familiar to commercial estimators within the building, construction, and civil engineering sectors. Instead of relying on a single value, as an output from the estimating process, using a three point estimating approach provides an “optimistic”, a “pessimistic”, and a “realistic” value, which therefore starts to consider any inherent uncertainty in the figures.
Three Point Estimating in Early Stage Carbon Assessment
Circular Ecology have taken this approach and applied it to early stage carbon estimating and assessments. Many construction project carbon assessments often take place at the design stage, where there is still the largest opportunity to implement impactful decarbonisation actions. Subsequently, there is a larger inherent uncertainty expected within the results due to many variables such as supply chain considerations, ground conditions, and procurement processes, to name just a few.
Early stage carbon assessments will often make use of carbon datasets for generic materials, along with other published assumptions and scenarios as their basis. This is considered an acceptable approach at early project stages, as many of these decisions are either subject to change or still being decided, but can be considered to have higher levels of uncertainty.
To mitigate this, carbon factors, such as those used within a carbon library, can be built to provide an uncertainty range, developed by understanding the plausible maximum and minimum values for that type of material or product.
Instead of applying blanket minimum and maximum values, our approach is much more grounded in plausibility. This can be achieved through the review of available Environmental Product Declarations, Life Cycle Assessments, or via literature studies and other research. Statistical analysis is then applied to give the plausible minimum and maximum values.
For example, at the design stage, a specific supplier of structural steel may not yet have been chosen, and so the assessment would instead utilise a generic material database (such as the ICE Database) and a generic factor for steel, which is calculated as an average carbon impact for steel products globally.
During the construction stage, it could then be decided that a steel produced using EAF (electric arc furnace) is to be procured. As the design stage assessment utilised a generic (global average) carbon factor, this assessment of the steel would be observed as having a much greater impact, compared to the lower carbon impact expected from an EAF steel.
Applying a three point estimating approach to this scenario would help to bridge the gap between the “generic “design stage assessment and a more specific “as built” assessment, allowing a greater understanding of the possible variations, decarbonisation potential, and maximum or minimum plausible ranges.
This can be a particularly useful way to present outputs when aligning cost and carbon reporting, especially when cost estimates may already use a three point estimating approach.
There is always an inherent level of uncertainty when undertaking carbon assessments, and it is difficult mirror the exact real world accurately, even when using the highest quality data available. Implementing a three point estimating approach to carbon assessments can help manage this uncertainty, gain a better understanding of the likely best and worst case scenario impacts, and allow for a more targeted implementation of suitable decarbonisation actions to achieve the most favourable outcome.
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If you are interested in using three point estimating to better manage uncertainty and identify real decarbonisation opportunities within your project, our team would be happy to help.
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