Replacing the electrical mast flashing where a one-piece boot cannot go over the wires is a simple 8 nail installation that takes under a minute. Repairing a bad flashing only takes a couple minutes and the old flashing doesn't need removed, Garrdal can enclose it. See the template on the installation page.
Rapidly increasing conversions to or new installations of mid and high efficiency furnaces are another example of where a one piece boot can't be pushed over a pipe. Non-condensing units are typically vented through the roof and have a "hood" on the concentric pipe, many of these vents are on the front of a house, certainly not a place you want a "re-used" existing flashing or ugly exposed clips showing.Installing a Garrdal 2 piece flashing saves time and has a one piece appearance. More important, the UV resistant materials aren't going to be a future issue.
Garrdal is an American made 2 piece flashing that is designed to go around roof top obstacles such as wire masts, high efficiency HVAC stacks or other circular penetrations up to 5 inches. A split boot alternative that has a single piece appearance. UV resistant with tear away ribs allowing the flashing to adjust up to over 5 inch diameter.