What does carbon footprint analysis mean and how do you perform it?
With the current building volume, the carbon footprint of construction at the national level accounts for up to one-tenth of Finland’s annual greenhouse gas emissions. These emissions are generated without delay instead of gradually over the course of decades. That is why the pressure to reduce emissions from construction and buildings is heavily focused on the emissions currently produced. Life cycle assessment (LCA) is the right tool to assess these emissions and thus to identify the potential for reduction.
Concepts and their interpretation
Carbon footprint in general refers to the greenhouse gas emissions generated by a product or service. The concept has been named according to the most significant greenhouse gas – carbon dioxide (CO2) – and the other greenhouse gases, which in practice refers to methane (CH4) and nitrous oxide (N2O), are taken into account by converting their climate impact into carbon dioxide equivalents (CO2e). In the case of the carbon footprint of buildings, this refers to the climate impact over the life cycle of a building. A standardised step-by-step breakdown for the life cycle of buildings has been determined to contribute to a more harmonised approach. EN 15978 determines the different stages of the life cycle of a building:
- A: Pre-use stage (product stage and construction stage)
- B: Use stage
- C: End-of-life stage
- D: Impact beyond the system boundary
There is a slight margin for interpretation in many of the definitions, and the Finnish terms, in particular, have been somewhat unestablished for a long time. For example, “hiilijalanjälki” or “carbon footprint” can refer to the entire life cycle assessment or to the annual emissions of a building (without any consideration of the life cycle impact). Vähähiilisyyden sanakirja, a dictionary compiled by the Green Building Council Finland (FiGBC) in the spring of 2020, is a praiseworthy attempt to standardise the terminology and definitions – the undersigned also participated in the background working group.
Calculating the life cycle carbon footprint of a building
The above-mentioned EN standard serves as the basis for the calculation of the carbon footprint of a building during its life cycle. In Finland, life cycle assessments based on the standard have been carried out since 2013 on the basis of a building life cycle analysis guideline (Rakennusten Elinkaarimittarit or REM) published by the FiGBC. REM is also the method used in the carbon footprint rating of the Finnish environmental classification RTS.
Climate policy pressure causes an increasing pressure to address and control the climate impact of buildings at the national level with a more comprehensive approach than mere energy consumption during use. To this end, the Ministry of the Environment has developed a national carbon footprint analysis method (YM julkaisuja 2019:22), the first pilot phase of which ended in June 2020. An update of the method is expected in 2021, and it will become a tool for regulatory control by the end of the 2020s (a mandatory “C figure” for building permits) in the same way as energy efficiency has been controlled with the E figure for a long time now.
The LCA criteria for the international environmental classification systems LEED and BREEAM require a similar analysis, but they are quite clearly different due to their different limitations and coverage. In practice, REM and YM are the methods used in Finnish construction projects for carbon footprint analyses. They have many similarities, such as the fixed reference period for the use stage (50 years), as well as similar calculation principles for building materials and energy during use.
For GBP, we offer the results of analyses according to our own analysis and reporting model and the REM and YM methods in the same report.
Practical implementation of carbon footprint analysis
In practice, a carbon footprint analysis is based on building design data. Emissions during the product stage are included in emissions at stage A, including the acquisition of raw materials for building materials, emissions from transport and manufacture, as well as emissions from the construction stage, including transport and construction site operations. In practice, the required important initial data consists of the quantities required for the design solution from, for example, the building element estimate or the developer’s bill of quantities or data model. The emissions for all the building elements are calculated on the basis of the quantities and the design data (the architectural and structural plans). The sources of product-specific emission data include Environmental Product Declarations (EPD), which contain standardised life cycle assessments at the product or product group level, such as for gypsum boards, concrete reinforcement bars or sawn timber.
Energy consumption of the building during use forms the most significant part of the emissions during the use stage. The YM method aims to achieve comparability between buildings, in which case it is important to use harmonised consumption data as the initial data for the analysis: the analysis is based on delivered energy according to the E figure analysis. The REM guideline instructs to use the most accurate energy consumption estimate as the initial data for the analysis – the E figure analysis is only secondarily used in cases where a more accurate simulation based on the actual usage profile is not available. Emissions during the use stage also include all required building element replacements during the review period – these are assessed on the basis of the estimated technical service lives of the structural solutions and chosen materials.
Other life cycle parts of lower significance can be considered on the basis of type values, especially where actual data is not available yet at the design stage or decisions on the solutions have not been made yet.
Results and utilisation of the carbon footprint analysis results
The final result is a report on the carbon footprint during the life cycle of the building. The sum total, in the format of “the carbon footprint of the building is 3,570 tCO2e”, is not a particularly interesting piece of information in itself, and in practice, the results are most useful if the report is sufficiently detailed. Reporting the emissions per net heated area makes the figures comparable, and a study of the different life cycle stages will genuinely reveal whether the emissions from the solutions are high or low.
In the case of stage A, splitting the emissions of the product stage into more detailed figures than the total emissions will offer concrete information about the design solutions that comprise the site’s total emissions. We use the division into building elements pursuant to the Finnish Talo 2000 (Building 2000) classification system in reporting – it provides an appropriately detailed way of classifying building elements in a standardised yet easily understandable manner. A well-established reporting practice also allows us to present the project’s emission level per building element compared to the average level for new buildings.
In terms of energy consumption during use, it is essential to understand how emissions are distributed between the different energy types, as well as to what extent large or small emissions are due to the characteristics of the local energy production or the energy efficiency of the building or its own energy solutions, for example. Furthermore, the differences between the YM and REM calculation methods are emphasised in the calculation of energy during use – comparing these helps to understand how the different calculation methods emphasise the relative share of the different life cycle stages in different ways: REM emphasises emissions from energy during use, while YM focuses on emissions from building materials.
When the carbon footprint analysis is performed as a declaratory analysis based on completed plans, in many cases there is no longer any practical opportunity to influence the carbon footprint during the life cycle of the building. In such cases, the value of the analysis lies in increased awareness and comparison with other buildings, as well as the opportunity to use the carbon footprint data in corporate accountability reporting or communication, for example. Meanwhile, if the analysis is performed at an earlier stage of the project, the carbon footprint calculations can provide a clear guiding effect: when the design process can be combined with the carbon footprint analysis results, it is often possible to reduce the carbon footprint by making the right design solutions – both in terms of structures and energy.
In practice, the cases mentioned above can also be combined: early stage plans can be used to create a preliminary carbon footprint analysis that can be used to guide design, and the analysis can be updated after completion of the building (or design), which allows for a precise analysis of the carbon footprint of the final solution.