While the quality certification of windows and doors remains a major objective for professionals in the thermal insulating joinery business, the German institute IFT Rosenheim makes available a full range of services which covers testing, technical analysis, conformity assessments etc. Although it may seem an undue approach referring to such seemingly simple products, checking of the operation of every component and the way they are integrated in the final product are important conditions for compliance with the intended use. Virtually, every element has a distinct role, acting together as a winning team: frame offers stability and contribute to an attractively designed, handles have a major impact in terms of operation and safety, the joints in the corners secure the necessary stability, the hardware systems ensure proper operation and safety, glass packages provide the transparency and a high degree of insulation, gaskets contribute to an optimal level of tightness etc. Although the harmonized European standard provides a relatively limited number of tests (impermeability to air/ water, wind resistance and safety issues) the experts have repeatedly demonstrated that, for obtaining a performance like the one provided in the energy efficiency directive, it is necessary to test many more features than those aforesaid. Among the most important properties to check are: mechanical strength, thermal and sound insulation, burglary endurance, reaction to repeated opening and closing actions, solar control, variations at climate changes, the fire resistance, the bullet impact etc. Also, in the process of installation, the most common defects identified by experts refers to curved frames, low water/ air tightness, malfunctions of the hardware systems etc. One of the frequent errors generated by wrong processing involve the gaskets, in this case being inherently compromised the overall level of tightness. Also during installation, often appears open spaces especially in the drainage area, which causes a reduction in the degree of thermal insulation.