Home » Carbon calculators for the built environment – why they don’t add up

Carbon calculators for the built environment – why they don’t add up

Published: 06/06/2023

Reducing carbon emissions is one of the biggest challenges facing our industry. 40% of GHG (greenhouse gas) emissions come from the built environment, and if we do not act immediately this figure could double by 2050. With the wide variety of carbon calculators on the market, it would appear progress has been made in finding a solution to the first part of the problem – calculating carbon.

It seems simple enough, with these figures the industry can begin to make better, informed decisions about the types of materials and components used in any construction project.

But how are these carbon calculators arriving at their assessments? Compare the results of one carbon calculator with another and you’ll find the figures vary considerably. What’s the reason for this?

Despite the good intentions behind many of the carbon calculators out there, here’s why they don’t add up…

We need four things to make consistent carbon assessments of our projects and have a better chance of driving down emissions:

  • Methodology: a consistent, industry-agreed methodology that clearly outlines what will be included in the calculation
  • Data: A consistent data source used in the calculation
  • People: Suitably qualified people to do the calculation
  • Regulation: Regulation or certification to make sure that the methodology and the data is being used correctly

And here’s our assessment of where we stack up as an industry against each one.



The industry has widely adopted the RICS (Royal Institution of Chartered Surveyors) Standard on whole life carbon assessments, but the application of the standard varies in the tools and calculators seen in the industry.

The various tools and calculators available today measure and include different things – some focus on the emissions of the initial construction, others include the in-use stage, some even include the end-of-life stage but often these are calculated differently.

The methodology also needs to change depending on the stage that the project is at. At the early stage of design you won’t necessarily know the materials you’ll be specifying, so the calculations you need to employ will have to change.



Unfortunately, we don’t have a rich history of carbon data to draw upon. Although EPDs (Environmental Product Declarations) are becoming more common they’re not available for every construction product. In some cases, the EPDs that are available for a product don’t have the information needed – mandatory fields aren’t completed and critical pieces of information such as the unit of measure aren’t identified, or consistent, with other products of a similar nature.

Other assumptions – life expectancy, installation process and what happens at the end of the life of the product – also have a dramatic impact on the figures used. Something, again, there are inconsistencies in.

Because of the lack of historical project data, we also find ourselves with the challenge of not being able to understand if our assessments are good, bad, or indifferent. We simply need to know these benchmarks, to ensure we’re confident we’re making the right decisions on our projects.

We also need to make sure we have a data feedback loop. Assessing a project’s emissions before construction is one thing – making sure we understand the emissions during and after construction and throughout its life is something else. We need to make sure we capture the ‘as built’ information and that this is fed back to help improve and refine our assessments in the future.



Currently anyone can complete a whole life carbon assessment, qualified or not. This is likely to present issues, as understanding on applying the methodology will vary dramatically. As an industry we like to confuse ourselves by using terminologies and acronyms.

These need to be understood by anyone undertaking an assessment, let alone a collective understanding of how and what to measure and report.

The likely outcome is that people without a common level of training and qualification will interpret things differently during assessments – even if we adopted a single methodology, calculation, and data set.



There is currently no industry-wide regulation to ensure carbon calculators use consistent methodologies, are operated by appropriately skilled professionals, or use consistent data. Until this is resolved by the industry there will continue to be inconsistencies in the calculations.

We’ll also be limited in our ability to accurately benchmark, learn from each other, and drive down emissions in the built environment.


What is the answer?

We’re undoubtedly all trying to drive this critical issue forward. We’re making good progress on several things –the use of a common methodology through the RICS standard and improving the availability of carbon data through the BECD (Built Environment Carbon Database) and BCIS.

But we are still at the early stage of our journey and time is against us.

To reach our goal of lower emissions, however we plan to solve the issues we need to work together, share our insights, and continue learning.

We need to overcome our fear of sharing data, information, and experience. This isn’t an issue we can solve remotely with pockets of activities.

Without meaning to sound like Yoda, the more inconsistent methodologies, databases, and calculators we produce, the greater the risk of creating more confusion and stalling our progress of reducing emissions in the built environment.

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