The current level of energy efficiency investments in the rental housing sector is in danger of missing EU policy targets to be reached by the year 2020. It’s possible that the goals are not being met due to a wide variety of reasons. Of great importance are especially different economic and political conditions for energy saving investments among the European member states. Furthermore the respective legal regulation in many states might still lead to “split incentives’ barriers” e.g. the landlord-tenant disincentive in the rental housing sector. Also a general lack of transparency and easy to process data is a core challenge for market participants. Therefore it is important to create a unique framework in order to assess the commercial viability of energy efficiency retrofitting in the rental housing stock. Besides calculation tools and models the assessment also has to take into account the inherent characteristics of the specific national rental markets, rental regulations, tax regimes etc. In order to ensure that such an approach is user friendly and widely used, a Web based solution will be needed. In our paper we will present a Web based concept to collect, normalize and process relevant data in order to ensure individualized results for the various investors types, legal environments etc. For that reason we will present a general network architecture using Web based technology. Here we put special emphasis on user friendly data processing as well as privacy & security. Due to the fact that the investment conditions for energetic retrofitting’s are varying considerably in Europe and furthermore input data is not static we need a flexible automatic processing tool that compute the data accordingly. For that reason we will present efficient algorithms and a universal data model.