Today’s commercial buildings need to be flexible because in many instances the exact use to which a given building will be put is not defined during the planning or construction phase. Moreover, the type of use often changes after completion, e.g., due to tenant turnover. FassadenSystemLüftung GmbH (FSL) of Mannheim provides architects, builders and ventilation engineers with a flexible solution to this problem: decentralized modular ventilation units. These modules, which have vents for air intake and expulsion, are integrated into the facade of the building’s skeleton structure. Depending on the function modules installed, decentralized ventilation units are used as air intake, expulsion, or recirculation units or as combined air intake/expulsion units with or without heating or cooling capacity. This high degree of versatility is achieved through function modules that need only be inserted into the main modules, which can be outfitted with heat exchangers, fans, air filters, volume flow controllers or valves. If no ventilation functions are realized, the modules are thermally and acoustically insulated. FSL’s decentralized modular ventilation units constitute the centerpiece of a decentralized ventilation/heating and cooling system that enables architects to design flexible buildings. The modules can be installed in windows, balustrades or in the building’s subfloor. These units (approximately 5,500 of them) are being installed in the Investment Banking Center (IBC) in Frankfurt, which is currently under construction, and are to be used in other buildings as well.