What is the primary purpose of plumbing jacks on a roof?

The primary purpose of plumbing jacks on a roof is to create water-tight seals around vents. Plumbing jacks, often made of rubber or metal, are specifically designed to fit around plumbing pipes that extend through the roof. Their function is to ensure that water does not enter the building through these vent openings, which are critical for the drainage and ventilation of plumbing systems. Proper sealing around these pipes helps to prevent leaks that might lead to water damage or mold growth inside the structure.

While ensuring a watertight seal is the main function, plumbing jacks may have additional roles, such as working with the roof's overall drainage system or being compatible with certain roofing materials. However, their primary and most crucial task remains to protect the interior from water ingress at these vulnerable points.