Single ply roof guarantees usually cover 15-20 years, but many roofs last 25-40...

https://wiki-neon.win/index.php/What_Maintenance_Records_Should_I_Keep_for_a_Commercial_Roof%3F

Single ply roof guarantees usually cover 15-20 years, but many roofs last 25-40 years in practice. The difference comes down to things like weather, wear and tear, and maintenance