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Can TPO Be Installed Over Old EPDM?

Posted: 2/1/2021

Yes. Recovering with TPO is a great option for a building with an aging EPDM roofing system. It’s easy. It’s far less costly and disruptive than a full tear-off. And the result is a durable, low-maintenance, energy-efficient new roofing system.

The EPDM membrane should not be recovered “as-is,” however. To make any future leaks far quicker and easier to find and repair, the old membrane must first be cut into pieces no larger than 10 feet by 10 feet. If the EPDM is left watertight, any water that gets in will pool on top of it. The leak will go unnoticed and unaddressed, leaving the roofing system susceptible to extensive damage. Cutting the old EPDM membrane helps ensure that the leak will manifest itself inside the building quickly, allowing it to be repaired promptly.

If a system warranty will be sought, a coverboard or slip sheet also may be required. The following is a brief guide. Further details can be found in the Mule-Hide System Specifications linked below.

  • Ballasted Systems: As a minimum, Mule-Hide HP Protective Mat must be used as a protective slip sheet between the new TPO membrane and the old EPDM membrane. When the old ballast will be reused, it also is advisable to place a protective mat between the membrane and ballast, since debris tends to get lost in ballast over the years and could puncture the new membrane.
  • Mechanically Attached Systems: No coverboard or insulation is required. If desired, insulation may be placed under the TPO membrane to enhance the building’s energy efficiency.
  • Fully Adhered Systems: A coverboard or insulation must be placed and secured between the old EPDM membrane and the new TPO membrane to provide an appropriate substrate for the adhesive to bond to.

When an EPDM roofing system has reached the end of its useful life, recovering it with a new TPO membrane is a cost-effective option that will deliver years of watertight, low-maintenance, energy efficient performance.


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