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

https://daisydustmaid.com/overlay-vs-full-replacement-for-a-single-ply-roof-when-does-overlay-make-sense/

Single ply roof guarantees, usually 15-20 years, cover workmanship and materials but aren't the full story. These roofs often last 25-40 years if properly maintained. To get the most from your roof, arrange annual inspections and clear drains regularly