Single ply roof guarantees, usually 15-20 years, cover materials and...

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 materials and workmanship but don’t always match the actual roof life, which can be 25-40 years with proper care. To get the most from your roof, arrange regular inspections and clear drains annually