In order to shield the indoor environment from the exterior most building components are assembled out of several layers of materials to meet different performance requirements (watertightness, airtightness, thermal resistance, stability etc). In that regard windows and doors are usually the weak spot of the building because it is a transition from the building component to the glass where all the different materials and functions are literally forced together. On top we want them to open and close, so that interface becomes even more crucial and we need to use somewhat exotic fabrics to rise up to the challenge (the bill will rise accordingly). Strangely enough, this research department is much too often left to the industry. Pressure equalisation is the basic principle where windows and doors derive their performance from, but how can this be realised, and what are the main parameters that influence it? As in walls and roofs we can distinguish different elements in the window casement that will fulfil those needs and influence the performance: the section, joggles, gaskets and fittings (handle, gearbox, locking bar, corner pivot, stay, hinges…). Using high frequency measuring equipment the influence of the different elements are examined in both dry as well as rainy conditions during static and dynamic pressure differences. The pressure equalisation in the chamber is dependant on the collaboration of the profile and the gaskets, the design of the vents and drainage holes, and the fine-tuning of the fittings. Analysing the performance of windows and doors one comes to the conclusion that the European Standard EN 1027:2000 may not properly benchmark the watertightness: certain damage initiation phenomena are underestimated in the current procedure.