The vent stack is part of the plumbing system. Its purpose is to permit adequate circulation of air in all parts of the sanitary drainage system and to allow a means for sewer gas to vent harmlessly to the atmosphere. All homes should have vent stacks. The absence of a vent stack usually indicates that the plumbing system is not properly vented, almost always a violation of the plumbing code. As you inspect the roof, look for a pipe that projects through the roof and terminates about 8 inches above the roofline. In newer homes, the vent stack is usually fairly obvious. In older homes, however, the vent stack might be missing or at least not visible when looking at the roof. On occasion, I have found vent stacks that terminate in the attic. This condition is a violation of the plumbing code; the vent stack must extend above the roofline so that the escaping gases can discharge to the outside.
In some older homes, when kitchens or bathrooms are renovated, vent stacks are often run up along the outside of the building to a point above the roofline. (See FIG. 3-6.) If these homes are located in the northern part of the United States, this type of installation is undesirable. Because of the moisture in the escaping gas, during cold weather it could freeze over and eventually block the pipe. Sometimes you find vent stacks that terminate near a window. (See FIG. 3-7.) This installation is also undesirable because the discharging sewer gas might seep into the house when the window is open.
PULL CHAIN AND RING
For vent stacks that terminate above the roof, very often you’ll see a black ring at the base of the stack adjacent to the flashing. This black ring is asphalt cement that has been used to seal the joint. This joint is vulnerable to leakage and should be periodically checked. On one inspection, I found water dripping from a ceiling tile in a suspended ceiling located two levels below the roof. When I lifted the tile, water came cascading down. After the initial shock and after all the water had spilled away, it became obvious that the water was not caused by a leak in the above laundry room but had collected during the previous day’s driving rain when water had leaked into the structure through the small crack between the vent stack and the flashing. This area should be periodically checked and sealed as needed.