Single ply roof guarantees of 15-20 years cover material and workmanship, but...

https://magic-wiki.win/index.php/Are_Manufacturers_Honest_When_They_Say_Membranes_Outlast_Guarantees%3F

Single ply roof guarantees of 15-20 years cover material and workmanship, but the actual service life can be 25-40 years with proper care. Factors like weather, maintenance, and installation quality all play a role