As the energy efficiency of new buildings begins to be at a cost-optimized level in Europe, the focus is shifting towards CO2 emissions during the construction phase. The maths in calculating the carbon footprint of producing the building materials is basically straightforward: The carbon footprint equals the mass of building materials multiplied their CO2 emissions/kg. It is thus obvious that timber structures, with their light weight and lower emissions per kg will score a lower carbon footprint than other materials. However, in reality it is not that simple because carbon footprint calculations involve a large number of question marks related to system boundaries and different lifecycle scenarios. In carbon dioxide emissions, the time perspective is not very simple. Do we want to radically reduce CO2 emissions now and not think about how it will affect future emissions, or should we consider the development of emission reductions over a horizon of tens of years?

Different materials have advantages over different lifecycles. The positive side of timber structures is that they work as carbon sinks in the building as long as the building is in use, but after demolition, the structures are usually used as energy waste, and the carbon dioxide bound in them is released back into the atmosphere. In addition, if logging and wood construction are now significantly increased, it will reduce the carbon sequestration capacity of forests, as a regenerated forest will only bind the same amount of carbon dioxide after decades. The steel production stage generates a lot of emissions, but once produced, steel circulates virtually forever and contributes to the reduction in future steel production emissions proportionately to the amount of recycled steel used. Steel structures can also be easily implemented so that they can be quickly dismantled and re-used in the future with little refurbishment. The final carbon footprint depends heavily on how different lifecycle phases are weighted. These priorities have not yet been defined and active debate on the subject is desirable when European countries develop their own regulations on carbon footprint reductions in buildings.

Sustainable construction aims, of course, at more than just carbon footprint. If a cap on carbon footprint is defined for different building types as a separate measure, will this lead to a low carbon footprint at the expense of other sustainable construction indicators? In the German DGNB environmental certification, carbon footprint is only one element in the environmental quality of a building. Other criteria for a sustainable building include: the technical, economic, operational and process quality of the building. Some concrete measures from these criteria include, for example, building flexibility and adaptability, noise insulation, façade maintenance, and demolition or reusability of structures. Metals meets well many of those criteria and by their very nature are durable, low maintenance with minimal running costs, easy to identify and dismantle whilst retaining their market value and easily returned to the value chain.

The calculation system in regulations must not be too complicated, but it’s clear that carbon footprint alone can’t define the sustainability level of buildings. Designers and the industry need to be given an opportunity to make innovative and sustainable solutions using all materials.