TPO and PVC membrane are heat welded as the rolls and flashings are installed. This provides a stronger seam than EPDM provided the welding is done properly. If the welding is done poorly then the seams/flashings may fail after a period of time. Some of the problems found in the plastic based membranes occur from the different chemical make-up. Older versions of plastic membrane could crack and shatter in below freezing temperatures. Splits and holes can also occur. Seams and flashings welded properly should last as long as the membrane. Slices and cracks are the most problematic issues with plastic based single-ply membrane. Proper patches require heat welding a piece of similar material. Check for ponding (see special ponding section on other page).