Because EPDM rubber has a lower puncture resistance, installation with a protective geotextile underlayment always recommended. Use of an approved underlayment is typically required to meet warranty requirements, since it prevents punctures from rough or rocky ground.
Even ground that appears smooth and free of rocks at the time of installation may encounter damage from rocks that rise from the soil over time. With such a long lifespan, it's a good idea to cover that contingency with a protective layer. A secondary benefit from the use of a non-woven geotextile underlayment is that it allows the ground underneath to breathe, preventing the formation of gas bubbles that may push your liner up from the bottom.
