Several factors influence the performance of modified bitumen flat roofs in asphalt or bitumen modification systems. Key factors include the type of polymer used for modification (such as SBS or APP), the application method (torch-applied, self-adhered, or cold adhesive), environmental conditions during installation, and the roof’s slope and drainage. Additionally, the quality of the underlying substrate and proper detailing at seams and penetrations are crucial for ensuring durability and waterproofing effectiveness.