Description: For the new installation of the Hi•Art irradiation system, a new radiation protection structure was built next to an existing radiation protection room. In order to enable the construction work to be carried out during ongoing operations, the adjoining room had to be adapted to the new requirements within a weekend. For this purpose, the existing room was uncovered and provided with a facing shell. The space created in this way was filled in layers with a bulk mineral filling and compacted. The use of Forster Sandwich Construction® and the associated high degree of prefabrication made it possible to realize the project within this short time window.