Single ply roof guarantees, usually 15-20 years, cover defects but don’t always...

https://redditchstandard.co.uk/lifestyle/how-long-does-a-single-ply-membrane-roof-really-last-a-building-owners-guide/

Single ply roof guarantees, usually 15-20 years, cover defects but don’t always reflect the roof’s full lifespan, which can be 25-40 years with proper care. To help your roof reach its potential, arrange annual inspections and clear drains regularly