There is a strong trend to industrially produce multi-storey light weight timber based houses. This concept allows the buildings to be manufactured to a more or less prefabricated extent. Most common types are volume/room modules or flat wall and floor modules. When assembling the modules at the building site, elastomer isolators are used in several constructions to reduce flanking transmission. The sound insulation demands in the Nordic countries are relatively high and therefore the flanking transmission must be well controlled, elastomer isolators is one choice. Decoupled radiation isolated walls is another. There are though no working studies or mathematical models of the performance of these isolators. They are only treated as simple mass-springs systems that operate vertically. In this paper there is a first approach of an analysis of the structure borne sound isolating performance of elastomer isolators that are separating floors and walls. The performance dependence of structure type is also presented. An empirically based regression model of the insertion loss is derived. The model will be based on measurements of more than ten field installations. In this paper the first three are presented. A goal is that the model can be used for input in future SEN prediction models for modeling of sound insulation.