Single ply roof guarantees usually cover 15-20 years, but the roofs often last...

https://www.bookmarkidea.win/single-ply-roof-guarantees-usually-cover-15-20-years-but-the-actual-service

Single ply roof guarantees usually cover 15-20 years, but the roofs often last 25-40 years if well looked after. The guarantee mainly protects against manufacturing faults, not wear and tear or poor maintenance