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

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, mainly focusing on material defects. But in reality, these roofs can last 25-40 years with proper care