Ask the Builder

Roof Vent Ice

By Tim Carter
©1993-2010 Tim Carter

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Summary: A roof vent cap can keep debris out of the vent, but it can also ice up in the winter. This ice can block the roof vents. Can the cap be removed?

DEAR TIM: My vent pipe running thru the roof extends about 30 inches above the roof and has a metal cap on it to keep debris out. Ice formed at the end of the vent pipe and blocked it.  Do I need this cap on the vent, it seems to create ice and block it, Can I leave the vent pipe open with no debris cap on it? Cleon Shafer, Coram, Montana

DEAR CLEON: I can see why the ice forms, as you sure get cold temperatures there. The water vapor rising from the plumbing system readily condenses, and then flash freezes on the cap. As this happens continuously in bitter-cold weather, it's no wonder the plumbing vent clogs with ice. When this happens, the plumbing system will get starved for air.

The bottom line is that you can remove the cap. I can't imagine why you would need it in the winter. Not seeing your house, I would think it may have been put on to stop debris from overhanging trees. But if those are deciduous, they have dropped their leaves by now.

Once there is no snow or ice on the roof, I would periodically check the vent pipe to ensure it is free of any organic debris. If the vent system is connected correctly to the drain pipes, you can insert a garden hose into the vent pipe to flush debris into your sewer or septic system.

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