What is the minimum height that B-vent must extend above the roof?

The minimum height that a B-vent must extend above the roof is indeed 5 feet. This requirement ensures that the vent adequately disperses combustion gases away from the roof surface and nearby structures, thereby reducing the risk of carbon monoxide accumulation and ensuring proper ventilation. The 5-foot height requirement also helps to mitigate potential downdrafts that can occur with lower venting heights, which can lead to backflow of harmful gases into the living spaces of a building. Ensuring that the vent is sufficiently elevated is a key safety measure in residential and commercial building practices where gas appliances are used.