What happens to EPDM over time?

• A. It shrinks, creating termination stress and is prone to failures at terminations, penetrations, and seams under tension.
• B. It expands and becomes more flexible.
• C. It becomes completely brittle at all temperatures.
• D. It does not change.

Answer: (A)

The important idea here is how EPDM behaves as it ages in a roof system. Over time, this elastomer tends to shrink rather than expand. That shrinkage means the membrane pulls away from fixed edges and details—terminals, penetrations, and seam areas—where it is restrained or tied down. When the membrane tightens at these points, it creates tension and stress concentrations right at the most vulnerable spots. If those edges and flashing aren’t able to accommodate the pulling forces, seams can open or flashings can pull away, leading to leaks and failures under wind uplift or thermal movement.

In contrast, the notion that it expands and becomes more flexible isn’t typical of aging EPDM in service. Becoming completely brittle at all temperatures is not accurate for a well-installed EPDM membrane, and claiming it doesn’t change at all ignores the aging process that affects shrinkage and performance over time.

So, the best understanding is that EPDM shrinks with age, producing termination stress and increasing the likelihood of failures at terminations, penetrations, and seams under tension.