Abstract
The OnTop Project performed at Frankfurt University of Applied Sciences, competing in Solar Decathlon Europe 2014, aims to demonstrate an approach to the rising challenge of urban densification by the help of an extra construction on top of an already existing building. While architects work on the most profitable structure of the building, it is equally important to detect which buildings are actually suitable for this purpose. Through the spatial data (3D city model, solar-roof and buildings cadastre, orthophotos, thermal images and LiDAR data) an analysis was conducted, deriving acceptable buildings within Frankfurt meeting the appointed criteria. Unfortunately, data protection issues and the aim of making the entire analysis automatic left only few criteria usable. Some of them proved to be crucial: height, function and roof surface, while others were used to weigh the results and appoint each building to a suitability class. For instance, the concept assumed that re-modelling roofs is acceptable. It was stressed that no resettlement should occur. Therefore, one of the most essential criteria was to assess from the available data, whether a building's attic is inhabited. This question was mainly assessed by the derived average roof angle per building, small angles indicating less likely habitation. One of the biggest challenges of the project was to manage the huge amount of data, their accuracy and inadequacy as well as their different origins. The analysis yielded estimations, overlaid on building polygons, which may be used for this concept and further evaluation resulted in a possible number of built OnTop structures.