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

https://jasperotbu571.iamarrows.com/single-ply-roof-on-an-industrial-estate-with-metal-roofs-too-who-coordinates-it

Single ply roof guarantees usually cover 15-20 years, focusing on workmanship and materials, but the real service life often stretches to 25-40 years with proper care