Single ply roof guarantees often cover 15-20 years, but the real service life...

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

Single ply roof guarantees often cover 15-20 years, but the real service life can stretch 25-40 years if the roof’s properly looked after. Guarantees focus on material defects, not wear and tear or maintenance issues