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

https://angelojvrt605.wpsuo.com/approved-contractor-schemes-do-they-actually-matter-for-guarantees

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. The guarantee mainly protects against material failure, not wear and tear or damage from weather