Common Roofing Problem: Shrinkage

January 6, 2015

Shrinkage is most common on EPDM or modified bitumen roofs. Its causes include aging of the material, poor installation, and UV exposure. A few decades ago, unreinforced rubber roof systems were plagued by shrinkage problems, but thanks to technological advancements and improvements to EPDM roofs, the problems have diminished.

The primary concern with a roof that is shrinking is the way it pulls the flashings at curbs, penetrations, and walls; this often leads to splits and cracks that allow moisture in, which can result in leaks.

Prevent It
Proper installation is the best prevention. With modified bitumen, crews should lay out the material to relax for 45 minutes, then when installed, alternate/stagger end laps. On an EPDM roof, use of ballast or a coating can prevent UV from heating the membrane and causing shrinkage.

Repair It
Replace affected flashing and curbs and relieve pressure and pulling by cutting the flashing, securing the field sheet with a termination bar or russ strip, and installing a new flashing.