Reducing the climate impact of construction is possible with the existing means
A low-carbon assessment method for buildings currently being developed by the Ministry of the Environment has greatly increased awareness of the life cycle carbon footprint of buildings. As regulatory guidance for construction based on the method is to be expected by the end of this decade, discussion around the topic has intensified. This year, a committee of the Green Building Council Finland (FiGBC) has worked on the definition of a carbon neutral building, but in this blog I will explain how the life cycle impact of buildings can be addressed in all types of projects.
Constituents of life cycle carbon footprint
The most important stages in the generation of the life cycle carbon footprint of a building are emissions during the manufacture of building products (A1–A3 Product stage) and the consumption of purchased energy during the use of the building (B6 Operational energy use). The relationship between the two depends essentially on the calculation method used (a method based on EN 15978, such as REM, compared to the YM method, where energy emissions are reduced), the building type and the structural and energy solutions.
Regardless of the above parameters, a common denominator for these emissions is that the product stage emissions are generated at the very beginning of the building’s life cycle.
In-use energy consumption emissions are generated over a longer term during the life cycle and can also be influenced during the life cycle. Meanwhile, emissions at the product stage cause an immediate, significant carbon spike – that is why addressing them is of utmost importance from the perspective of the curbing of climate change. Steering projects in a direction that will reduce the carbon footprint is possible, and it does not necessarily mean increased construction costs.
Reducing the carbon footprint at the product stage
The carbon footprint at the product stage can be influenced by design solutions and procurement. Even in the case of conventional concrete construction, there are many factors that can be used to influence the carbon footprint, and this does not necessarily mean choices that will increase the investment costs. The principles of cutting down the carbon footprint can be reduced to simple rules of thumb, such as “avoid metals and use light-weight structures”, but only a project-specific review will provide a more accurate idea of what type of measures will have the greatest impact.
The diversity of exterior face materials often offers opportunities to influence the carbon footprint. A concrete sandwich exterior wall is an average solution in terms of emissions. Higher emissions will occur if the outer concrete shell is replaced with masonry – similarly, lightening of the structure (e.g. light-weight exterior face cladding, insulating plaster or a timber exterior face instead of the outer concrete shell) will reduce emissions from the exterior walls.
In terms of building frame solutions, many solutions based on steel structures or steel and concrete sandwich structures cause the highest emissions – in many cases, the emissions from a column-beam frame in an office building are clearly higher than those from residential buildings with a frame based on load-bearing concrete partition walls. On the other hand, there are often more realistic options for the frame solution of an office building than that of a residential building, because fire safety and acoustics requirements for residential buildings limit the freedom of choice. Timber construction offers significant emission reduction potential when compared to traditional concrete components, but replacing a concrete column frame cast on site with steel beams and columns and a timber slab system, for example, can lead to significantly increased emissions.
On the other hand, material choices are connected not only to design but also to procurement. Hence, different product categories are in very different positions in terms of emissions. There are only a couple of alternative manufacturers (or even a single manufacturer that has achieved a monopoly) for some products, which means limited opportunities to influence emissions by the choice of products. On the other hand, even a wide range of products and a diversified competitive position might not offer any clear emission reduction potential at the procurement stage if comprehensive manufacturer-specific emission data is not available.
Alongside the development of the YM carbon footprint method, a national emissions database project is underway to develop a database for generic emission data. It will harmonise carbon footprint analysis results and assist in the choosing of structural solutions and materials. However, product-specific emission data (based on Environmental Product Declarations or EPDs) will still be needed (and even more so) to highlight the differences in the carbon footprints of the manufacturers within the product categories.
For construction product manufacturers, this is a great motivator to prepare EPDs for their products in order to gain a competitive advantage within the product group with their eco-efficient products. At present, some product categories have relatively good EPD data to support emission comparisons, while manufacturer-specific data is virtually inaccessible in the case of other products due to lack of data.
The product stage reviews may be completely different in the case of different building types. In the case of small buildings, such as a day-care centre with a timber frame, the emissions from the frame may be very low – similarly, the emissions from the foundation and base floor of such a building may constitute a significant share of the total emissions at the product stage.
Reducing the carbon footprint during use
Reducing the in-use carbon footprint is a different topic when compared to the product stage. While the emissions at the product stage are generated right at the start of the building’s life cycle, emissions during use are gradually generated, although the general direction for the in-use carbon footprint has been already decided at the design stage. On the other hand, the regulation of energy efficiency in construction has been a familiar task for a long time now due to energy performance certificates, but the E figure analysis in an energy certificate does not directly apply to the carbon footprint.
When the E figure is calculated, coefficients based on primary energy consumption are used. They do not provide any information on the specific emissions of the energy types. With a significant reduction in the specific emissions from electricity production, this has led to a growing difference between the carbon footprint of energy use and the E figure. The specific emissions of purchased electricity have remained below the specific emissions of the average district heating network for several years now, and the carbon footprint of heating energy can be a fraction of the carbon footprint of district heating, especially if air source heat pumps are used. On the other hand, there are huge differences between district heating networks – high-emission district heating networks based on fossil fuel include those in Espoo and Helsinki, while in some towns the specific emissions of the district heating network have been very low for years due to the utilisation of waste heat from the forest industry or renewable fuels, for example.
The relationship between the calculation of the E figure and reality is a whole different story – the user plays a major role in the generation of the in-use carbon footprint. An energy survey cannot (and does not even try to) fully predict the actual circumstances. Instead, it uses simple calculation principles to present an indicator based on the building’s characteristics.
The carbon footprint of energy consumption can also be significantly changed over the course of the life cycle. In any case, building technology must be renovated during the 50-year review period as systems reach the end of their estimated technical service lives – and energy consumption can be influenced at many points. On the other hand, development of the specific emissions from purchasing energy will inevitably change the in-use emissions. The assumptions included in the YM calculation method on reducing emissions in the energy sector take this into account.
Other points of view and prioritisation
The life cycle carbon footprint is linked to a wide range of aspects other than the structural and energy solutions discussed above. The life cycle involves other stages during which emissions occur, and in addition to the life cycle emissions, buildings have different kinds of climate effects outside the life cycle, such as aspects related to carbon sequestration and the recyclability of products. However, from the viewpoint of curbing climate change, it is most important to focus on acute, important issues.
Reducing the carbon footprint of buildings does not require miracles, and it is possible in all kinds of projects, even though the design solutions are limited by a variety of preconditions. Life cycle assessment always involves assumptions and uncertainties, but this does not mean that it is not possible to assess the magnitude of the issues at the relevant level of precision and thus find concrete measures to curb climate change.
