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

https://andreocln282.lucialpiazzale.com/what-questions-should-i-ask-before-signing-a-single-ply-roof-contract

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years if well cared for. The guarantee mainly covers manufacturing faults, not wear and tear or damage from poor maintenance