Case studies were used to investigate the effect of double facades on the planning and dimensioning of building services systems and on the overall energy efficiency of buildings. The main result of these investigations was the finding that the energy efficiency of buildings with double facades depends on whether the use of the double facade makes it possible to dispense with entire building services systems (e.g. mechanical ventilation). If this is not the case, it can take up to 25 years until the additional manufacturing energy expenditure of the second skin is compensated by energy savings during operation. If, on the other hand, a complete technical building system can be omitted due to the double facade, this energy payback time is reduced to a reasonable period of time, in some cases even within 2 years. The case studies examined clearly show that highly efficient double facades can not only improve the energy performance of the building but can also significantly reduce the investment costs of the building services. Therefore, the cost-effectiveness of such a measure should not only be evaluated in terms of its potential for reducing energy costs, but always in connection with a possible reduction of investment costs for HVAC systems in the building. A mere reduction in the size of the building services systems usually does not lead to significant savings.