This thesis deals with the optimization of structural details for flat single-leaf roofs. In the first part of the thesis, 3 groups of structural details for flat roof (flat roof parapet, gutter at flat roof without overhang of the roof cladding, intersection of the flat roof and vertical supporting structure) are characterized, classified and examined. In every group one of these structural details is designed with use of modern composite material based on secondary raw materials (still in development process). The theory describes the current issue of thermal bridges at constructions and applicable legislative documents. The next part introduces thermal engineering analysis (based on finite element method) of structures with annotated data outputs. The another main part of thesis provides with designed innovative optimization algorithm using multi-criteria decision analysis methods, which is then practically tested on the surveyed construction details. The conclusion summarizes the results and provides with improvements based on completed research.