The complexity of the residential house structures makes their condition evaluation difficult. Taking the human experts' thinking into consideration the linguistic approach seems reasonable, therefore the fuzzy set theory may provide a basis for creating an expert system. In practice, the assessment of some predefined attributes of building components may give a comprehensive value about the condition of the examined building on a relative scale. The data structure of building evaluation procedure makes clear that the fuzzy signature structure is helpful in analysis. The numerous building components that determine the character of the given building can turn to an unnecessarily large rule-base. The fuzzy rule interpolation and the corresponding sparse fuzzy rule-based knowledge representation could be a reasonably efficient structure for handling the building evaluation procedure. In this paper the fuzzy rule interpolation as a novel aggregation method in fuzzy signature structures is proposed. Its application is presented with a case study of roof structure evaluation of a classic urban-type residential house located in a historic district of Budapest, Hungary.