In timber concrete composite (TCC) floor systems the concrete contributes to increase of the stiffness and research is ongoing to develop large span TCC floor systems with less supporting walls to create both modular flexibility and wide-open spaces. Nevertheless, removing supporting walls can degrade structural performance against horizontal forces (Ferdous, et al., 2019). Meanwhile both the height of the structure and the type of floor diaphragm (rigid or flexible) has influence on the magnitude of the lateral loads transferred to the supporting shear walls. This is a challenge, not least when prefabricated elements are used; the individual elements have to be connected to form a continuous floor diaphragm. The main aim of this paper is to study lateral load transferred to the shear walls through the TCC floor with both rigid and/or flexible diaphragms in low and medium-rise timber buildings. The focal point of the study is the analysis and design of floor elements and connection systems connecting the TCC floor elements to each other as well as to the adjoining structure. The case studies for low and medium-rise timber structures have been analyzed both using finite element modelling and analytical methods based on both deep beam theory and beam or diaphragm actions depending on the height of the structure. The results in this study indicate that the magnitude of load transferred to the shear walls depends on both the height of the structure and the type of floor diaphragms. The structural performance in terms of stability can be enhanced by effective use of connection systems of TCC floor elements.