Single ply roof guarantees usually cover 15-20 years, but these membranes often...

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 these membranes often last 25-40 years in real life. The guarantee is about the manufacturer’s promise if something goes wrong, not how long the roof will physically hold up