A long service life is expected from modern wooden windows. This requires permanently tight window corner connections. As part of the research project DauerFen, constructive solutions for stabilizing the window corner were researched. The type of adhesion, the formation of joints between the longitudinal and transverse timber, and the use of joint sealing systems were identified as influencing parameters. The focus of the examinations was on a comparison of the solution variants under real conditions with direct weathering. It was furthermore investigated which amounts of wood preservative can be applied using the methods commonly used in window construction such as flooding or dipping.