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

https://blogfreely.net/rothesqlmw/what-does-a-bad-vapour-control-layer-do-to-a-flat-roof

Single-ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with the right care. Guarantees focus on materials and workmanship, not wear and tear or accidental damage