Prevent That Vent Stack From Freezing This Winter

December 19th 2011
Prevent That Vent Stack From Freezing This Winter

A common question that comes up every winter from homeowners across B.C., especially from those of you in the north or Interior of the province, is the issue of frozen roof stacks. The vent stack takes all the moisture and exhaust from within your homes water supply - like sinks, showers, toilets, floor drains and all sanitary drains - and exhausts them through your roof cavity.

The warm vapour moving up the stack must be exhausted, and as the moisture hits the sub-zero outside temperature, it condenses, freezes, and continues to build up until eventually, the roof stack will plug shut.

Some suggest that insulating the vent stack within the attic cavity will fix the problem, but the attic is not where the problem lies. Others suggest installing one of the various styles of sewer vents that resist plugging and are available from hardware stores and building centres, but these vents are costly. In any case, you can fix the issue without buying any alternate materials.


The higher the roof stack rises above your roof line, the more condensation to take place and build up within the pipe, so the easiest solution to prevent this from happening continually is to cut the vent stack shorter, giving the moisture a quicker route to dissipate into the open air. Be sure to cut the roof stack no shorter than six inches from the roof line and re-cap it with the appropriate vent cover. You may also want to wrap the pipe with foil insulation, such as Reflectix, within the roof cavity. This will keep the vapour exhausting through the pipe warmer, which in turn will help it vent more rapidly and exit your home faster, reducing the time the vapour has to freeze.

Its just that easy.