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

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

Single ply roof guarantees usually cover 15-20 years, but the actual service life can stretch to 25-40 years with the right care. The difference comes down to day-to-day wear, weather, and maintenance