Single ply roof guarantees, usually 15-20 years, cover product defects but...

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 product defects but don’t always reflect the roof’s full service life, which can reach 25-40 years with good care. To help your roof last longer, get annual inspections by an SPRA-approved contractor