Single ply roof guarantees usually cover 15-20 years, but the actual roof can...

https://sirachapete736.gumroad.com/p/how-often-should-a-commercial-single-ply-roof-be-inspected

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. Guarantees protect against defects, not wear and tear or poor maintenance