The purpose of this thesis was to examine the total content of phenols and total organic carbon in the eluate of three different wood species: sweet chestnut (Castanea sativa Mill.), European beech (Fagus sylvatica L.), Norway spruce (Picea abies L.) and Norway spruce protected by a copper-ethanolamine preservative Silvanolin%. The research also explores the change of the compressive strength of the samples. They were exposed to third class exposure in periods between 4 and 30 months. Soluble organic carbon in the eluates was determined by TOC analysis, whereas the proportion of total phenols by UV-VIS spectrophotometry. Furthermore, measurements of compressive strength were performed with the machine Zwick-Roell on air-dried samples. The results show that longer exposure time increases the share of extractives, which is reflected in the greater proportion of soluble organic carbon and / or total phenols. The increased proportion of extractives is mainly caused by bio-degradation of wood. Finally, the study reveals that compressive strength in all wood species is inversely proportional to the time of exposure to weather conditions.