The diploma thesis is focused on determination physical properties of spruce (Picea abies Karst.) and their influence on the thermal performance and other properties of window frame section. Thermally modified wood is performed at temperatures 160 ° C, 180 ° C and 210 ° for three hours. Its selected physical properties are measured and compared with wood without thermal treatment. The experimentally determined values of thermal conductivity of thermally treated and untreated wood are used to analyse the thermal performance of simple wood windows. The results are compared with the requirements according to STN 73 0540-2. The conclusions from experimental-theoretical research of thermally modified wood in the term of the application point for the production of building and joinery products are evaluated.