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

https://direct-wiki.win/index.php/What_Questions_Should_I_Ask_Before_Signing_a_Single_Ply_Roof_Contract%3F

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