Background Renovation using standard methods and materials based on fossil fuels and concrete binders encounters a number of problems that demand new and better solutions. Such materials hinder diffusion and often lead to dampness and mould, which results in long-term damage to a building. These factors are responsible for the bad quality and short lifespan of many renovated buildings. Higher quality can be achieved with improved knowledge transfer. Large gaps in knowledge, especially outside academia, are responsible for the poor performance of the renovation sector. Exisiting innovative solutions in the construction business are mainly suitable for new buildings and often do not comply with the requirements of older buildings. Moreover, knowledge of the use of renewable building materials is poorly resourced, and only a very few skilled professionals are able to carry out restoration work of historic buildings without causing long-term damage to the structures. Objectives The project partners' primarily aimed to reduce CO2 emissions caused by the construction industry, one of the most resource-intensive sectors. These emissions can be reduced by increasing the energy efficiency by an order of magnitude or more, and by using building materials with low-embodied energy, i.e. materials whose production and transport does not require large amounts of energy. The project focused on improving the environmental impact of the renovation sector by promoting knowledge transfer of construction methods that use renewable resources and natural materials; by gaining practical knowledge from demonstration sites; and by involving stakeholders across the building sector. It examined both the best technologies derived from the latest research projects, and traditional know-how on the use of renewable and locally available resources with a very low carbon footprint. Results The RENEW BUILDING project successfully demonstrated that the use of renewable and sustainable construction materials for the renovation of existing buildings can lead to impressive savings in terms of CO2 emissions and waste. Hence, the project proved that the renovation sector can make a significant contribution to the mitigation of climate change. For instance, the project consortium's tests showed that 17t CO2 equivalents can be saved in the production of building material per average single family house if renewable, climate-friendly materials such as straw, wood, or hemp are used. Moreover, reusing roof tiles, clay, and so on resulted in 82% less construction/demolition waste. Their sustainable renovation techniques amounted to economies of nearly 100% of petrochemical products, and considerably reduced traffic emissions, as materials were sourced locally. The project team tested different materials, combinations, and techniques for the main areas of renovation such as foundations, outer and inner wall insulation, windows, surfaces, ceilings, and roofs. These so-called 'prototypes' were implemented at two training sites in Böheimkirchen (Lower Austria) and Sarleinsbach (Upper Austria). They consisted of small or larger trial areas in the test buildings, i.e. one room would have two or three wall sections built/treated in different ways. In their quest for sustainability, the project partners combined research and practice, old and new techniques and materials. The latest trends in passive house design were employed side by side with techniques such as 'tadelakt'. This lime plaster has traditionally been used to waterproof interior and exterior walls of the riads of Morocco. Rediscovering and adapting it to modern requirements (energy standards, safety, liability, connection to modern material such as glass foam, modern production, etc.), the project aimed to bring the technique into the 21st century. In this context, the project team also built a lime furnace to locally produce burnt lime (calcium oxide, CaO) with properties suitable for the use in e.g. floor and wall coatings, 'tadelakt' surfaces, and others. The lime furnace reduced the environmental footprint, and showed that this important construction material can be produced locally. In this and other ways, the project boosted local product and service cycles, which are particularly important for small enterprises, and decreased dependence on imported goods. In addition, the use of renewable materials in housing has a positive effect on the health and living comfort of the inhabitants. The demonstration factor in the project was just as important as the innovation aspect: the consortium strived to involve craftsmen, architects, planners, and other professionals from the construction sector, in order to link practice and theory, and foster cross-disciplinary information exchange. The project team developed an innovative training scheme in the form of a series of training modules and hands-on experience at real building sites. In particular, achieving cost-efficiency is part of the training schedule to make climate-friendly renovation techniques competitive in the construction market. The training programme continues now that the project has ended. The RENEW BUILDING project partners are also keeping up dissemination and information activities, targeting experts as well as laypersons. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan/After-LIFE Conservation Plan (see "Read more" section).