The Master thesis follows the research focused on verifying the thermal performance of the traditional log structures with thermal insulation made of softboard fibreboard and sheep wool designed with and without vapour barrier. Log structures, natural thermal insulation of timber structures, vapour barriers and actual requirements for thermal performance of structures and components in accordance with the standard STN 73 0540-2 are described in the thesis as well. The research part of the thesis focuses on theoretical analysis of thermal performance and experimental research of moisture content of given log structures built in research building with in-situ conditions during the period of 2 years and 3 months. Theoretical analysis results in an assessment of thermal performance of structures in accordance with the standard. Experimental measurements result in the moisture content of individual materials in structures, relative air humidity and direction of moisture movement in the structures during periods of the year, influence of the vapour barrier on water vapour transition in structure, dew zone and period of possible condensation of water vapour, moisture content of the log structure for the biodegradation risk assessment. The result of the thesis provides final assessment of obtained findings and subsequent proposals for practice in designing timber structures.