PVC roof systems are often promoted as one of the best roof systems available. They have excellent UV resistance, hold up well against greases and oils, and have heat-welded seams. However, PVC also has a problem with cracking, shattering, and shrinking over time. This is a result of one major problem with PVC roof systems, which is plasticizer migration.
Plasticizer migration occurs as a result of the PVC membrane formulation. Most PVC products, like PVC pipe, PVC trim, and PVC decking, are solid, rigid products. In order to make PVC a flexible membrane sheet, the formulation needs to be altered. As a result, plasticizers are injected into the formula so that the membrane is flexible, making it able to be installed similar to other single-ply roof systems.
The problem is that with some PVC formulations, the plasticizer injected into the formula isn’t compatible. As a result, the plasticizer tries to separate from the PVC sheet, which causes the shrinking, shattering, and cracking that older PVC roof systems are known for.
In some manufacturer’s older PVC roof systems, the membrane was not reinforced. As a result, the entire roof system would shatter like glass, creating a total roof system failure in seconds. Today, almost all PVC membranes are installed with a reinforcing fabric. As a result, the shattering is typically contained to smaller areas of the roof system. However, when the roof shrinks, it can cause other major problems, such as the edge metal pulling away from the roof.
Higher-end PVC manufacturers have come up with a variety of solutions to this problem. Some have modified their PVC formula so that the plasticizer is more compatible. Others have substituted out the plasticizers, or a large portion of it, for KEE, an alternative product that doesn’t try to migrate away from the PVC sheet. However, KEE is substantially more money, making these KEE PVC roof systems far more expensive. Some manufacturers offer both formulations.
Regardless, almost every PVC manufacturer will claim that plasticizer migration is a thing of the past. However, even on some of these higher-end PVC roof systems, localized shattering can still be found as the roof nears the end of its life. Whether these newer formulations will fare better will only be determined down the road, after nature has had decades to throw everything it has at them!