Over the New Year’s holiday, many homeowner’s vent pipes iced over creating a possible hazardous situation. To prevent this problem, inspection and cleaning the top of the vents in the late fall, after all the deciduous trees have lost their leaves, is fundamental.
Even with regular maintenance, icing over of low roof vents can occur. One possible solution is to extend the vents higher up to prevent coverage with snow. While this may help prevent snow blockage, it may actually hinder the true solution to the issue.
The real cause of ice formation at the top of your vents is the loss of heat inside the pipe as it rises through your cold attic. If the pipe does not remain warm enough, the large amount of moisture in the air rising up toward the roof can condense and then freeze before it exits to the exterior. If you have older cast iron stacks, this is even more likely due to good conduction properties of the metal. An iron pipe will lose heat more rapidly than other ones, but even a more modern ABS plastic pipe can be subject to freezing.
The real key to preventing excessive heat loss and freezing of the wet air inside your stack is better insulation. Insulating the exterior of these pipes, mainly as they progress through your frigid attic space, may prevent this excess heat loss. While there may currently be a thin layer of fiberglass or other pipe wrap material around these stacks, it may provide only minimal help. Covering the stacks with better quality or thicker layers of insulation may be the only thing required to prevent freezing.
Adding more insulation around the bases, where the vents enter the attic, can also prevent quick cooling.