Single ply roof guarantees usually cover 15-20 years, but the actual roof can...

https://bravo-wiki.win/index.php/Is_Choosing_the_Membrane_Chemistry_the_Main_Decision_for_Roof_Lifespan%3F

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. Guarantees mainly protect against manufacturing faults, not wear and tear or poor maintenance