Sealing the Plumbing Stack

Another penetration into the attic! As you've probably guessed by now, we don't like 'em. Anytime there is a hole that goes into the attic, there is air loss. Though hidden between walls, the stack, or waste vent, is affecting the comfort and energy consumption of the building by allowing air infiltration / exfiltration between conditioned and unconditioned spaces.

Because the stack is usually close to water supply lines, drafts through these areas during freezing weather can cause the pipes to freeze. Most of us have had that experience before, and don't care to relive it.

Above is a thermogram of an unsealed plumbing stack on a newly constructed addition. This was taken during the summer while the homeowner was running the bathroom exhaust fan. In this image, yellow is warm and purple is cool. The effect of the air washing down inside the wall can be clearly seen in the center of the image. If this penetration is not sealed, come winter, cold air will rush down this wall every time she turns on the fan. Supply lines to the shower and toilet upstairs, and the kitchen sink and dishwasher downstairs share the chase containing this plumbing stack. These pipes are in danger of freezing.

Another problem is, when the fan is not running, warm moist air from inside the building is being lost to the attic, where it may cause problems such as ice damming, mold, or structural decay.

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