The aim of the diploma thesis was to detect the resistance of coniferous timber treated with selected flame retardants after exposure of its surface to radiative heat. One kind of tree species Norway spruce (Picea abies), which is most often used in construction, was tested.The treatment was performed with a typical flame retardant HR prof, and an atypical retarder, which is not commonly used in wood protection, an aluminum coating used to protect metal objects at high temperatures - Striebrenka.Samples treated with retarder, and untreated, verification sample, were heat-loaded by radiant heating from a radiation panel. When detecting the degree of wood degradation, the changes in the basic chemical composition were monitored, specifically the content of extractive substances, holocellulose, cellulose, hemicelluloses and lignin.The results indicate, that the chemical treatment of the timber by radiant heating changes the chemical composition of the timber, while the largest changes were recorded in the sample, which was not coated with any retardant at all. This sample showed a significant decrease in the carbohydrate component of wood, especially hemicelluloses. When comparing the level of degradation of samples treated with flame retardants, it is clear, that the HR prof retarder has a better effect compared to Striebrenka.Key words: spruce timber, HR prof, Striebrenka, extractive substances, holocellulose, cellulose, hemicelluloses, lignin