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

https://cristiansbrilliantblog.fotosdefrases.com/ponding-water-at-upstands-design-problem-or-maintenance-issue

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