Production and construction of window profiles are changing due to new aesthetic and functional requirements. More and more users choose windows which do not require any maintenance of a surface coating. Due to the mentioned fact, and because of the aggressive advertising of PVC windows, they are taking over a leading market share. Wood as a natural material for producing windows needs to be maintained, as deffects may appear soon, caused by bad surface finishing, mechanical stress, incorrect installation and other irregularities. Deffects on the surface finished wooden windows appear the most frequently on the lower parts of the window sash and frame, especially incorner joints. We studied the impact of corner joints on resistance of profiles of surface treated windows against ageing. We used 2 types of corner joints and produced them from wood of 3 different tree species: spruce, Siberian and Slovenian larch. We determined the changes of dimensions, weight, gloss, and colour. The results showed an advantage of dowel joints with many horizontal joints. Moreover, all the results of research confirmed that surface treated pine had some advantages comparing to other profiles. Based on the results and review of the market, we conclude that the installation of pine wood windows contributes to the reduction of CO2 in the atmosphere. By a careful installation and regular maintenance of the surface finishing better durability can be achieved.