Plant-based insulation materials as CO2 sinks?

The building sector is the most material-intensive sector and one of the most important drivers of global climate change. It is responsible for around 40 percent of global energy consumption, for 30 percent of greenhouse gas emissions and accounts for 36 percent of the waste generated in the EU. Following significant efforts in recent decades to ensure that buildings consume less energy and that renewable energy is increasingly used in the operation of the building stock, greenhouse gas emissions have been noticeably reduced in this area. However, over the entire life cycle of a building, its construction as well as the production of building materials also play an essential role, but one that has received little consideration so far compared to its operation. In modern buildings, the embodied greenhouse gas emissions resulting from the construction of the building are about as high as the emissions from its operation. Therefore, building materials that remove CO₂ from the atmosphere long-term have great potential to reduce the ecological footprint of buildings.

How CO₂ can be bound long-term

A new research project by a team of scientists led by Jannis Wernery from Empa's Building Energy Materials and Components Lab is based on the idea of binding CO₂ in newly developed insulation materials over the long term. To this end, plant-based raw materials – ideally waste products from agriculture and forestry – are to be processed into insulating materials for buildings. Most of the carbon bound in the biomass, which the plants have absorbed in the form of CO₂ from the atmosphere during their growth, can be permanently fixed by a special heat treatment; it remains bound in the resulting biochar throughout the life of the building – and even far beyond: Indeed, when the latter is deconstructed, the biochar can be introduced directly into fields. There, it increases the fertility of the soil and remains stable for centuries to millennia – unlike other plant-based building materials, such as wood or cellulose insulation, which release the stored CO₂ again when they rot or are utilized thermally.

"But there is still a lot to do before the idea can be put into practice," says physicist Wernery, who specializes in the research and development of insulation materials with his research group at Empa and is also collaborating with researchers at the Zurich University of Applied Sciences (ZHAW) on this new approach. Among other things, it is important to ensure that all the ingredients of the novel insulation materials are suitable for later use as "fertilizer"; a marketable insulation material must, of course, also be able to keep pace with established products in terms of thermal insulation and also guarantee adequate fire protection.

Empa researcher Wernery is convinced that biochar-based insulation could significantly improve Switzerland's CO₂ balance in the future – if it succeeds in meeting this demanding set of requirements. An initial analysis has shown that a realistic partial replacement of conventional insulating materials such as EPS or mineral wool with biochar could save a good half a million tons of CO₂ equivalents annually, on the one hand by avoiding emissions during the production of the conventional materials, and on the other hand by the long-term storage of CO₂ in the biochar. This corresponds to over one percent of Switzerland's total greenhouse gas emissions.

Financial support – from several sources

An ambitious concept with great potential – this was also the opinion of various funding institutions, which are therefore supporting Wernery's approach financially: namely the Minerva Foundation, which is committed to the sustainable use of natural resources, the ETH Board and the Swiss Federal Office of Energy (SFOE). Last but not least, the Climate Fund of Stadtwerk Winterthur recently granted a subsidy for the development of the basics, which comes from voluntary contributions of two Rappen per kilowatt hour of electricity purchased by the customers of Stadtwerk Winterthur.