Energy‐efficient building refurbishment has the aim of saving energy and thus reducing CO2 emissions. Increased energy efficiency of a building often implies reduced air exchange. Together with other indoor air quality problems, this may lead to an increase in indoor radon concentration (Rn‐222). In order to investigate the extent of this problem, measurements of radon concentration in energy‐efficient refurbished and low‐energy houses (passive houses) were carried out. Track etch detectors were exposed in each type of building over a period of 1 year. A reference sample of non‐refurbished non‐passive buildings was drawn from the National Radon Database for comparison. Buildings were selected that have the same radon relevant properties and were built on comparable geological subsoil like those investigated. The reference sample was compiled in such a way that the measured values from the rooms on the ground floor of the refurbished and passive houses were each assigned a measured value from the database. The statistical analysis shows that the houses refurbished for energy efficiency have a wider distribution of radon concentrations indoors than the non‐refurbished ones. Both the mean value and the median of the radon concentration have nearly doubled in buildings refurbished for energy efficiency. The difference is statistically significant. On the other hand, there is no significant difference between the distributions of passive houses and houses not refurbished for energy efficiency.

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Das Ziel von HyAdd3D ist es, mit neuer Anlagentechnik komplexe Bauteile additiv zu fertigen und gleichzeitig den Anforderungen einer Multimaterialfertigung gerecht zu werden. Das Projekt umfasst die Entwicklung einer hybriden Verfahrenslösung, welche in der Lage ist, neue Materialien mit funktionalen Zusatzstoffen zu verarbeiten. Der Beitrag beschreibt den HyAdd3D-Ansatz und beleuchtet den aktuellen Projektstand. Abschließend werden die aktuellen Ergebnisse zusammengefasst und ein Ausblick auf die folgenden Entwicklungsschritte gegeben.   The aim of HyAdd3D is to create complex additive manufactured components with novel equipment technology whilst simultaneously fulfilling the requirements of the multi-material manufacturing process. The project engages in developing a hybrid procedure solution that is able to process new materials with functional additives. This article describes the HyAdd3D approach and examines the current project status. All relevant findings are summarized to conclude and further developing measures are explained.

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