Single ply roof guarantees usually cover 15-20 years, focusing on material...

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, focusing on material defects rather than how long the roof will actually last. In reality, with proper care, these roofs can serve 25-40 years