A Soil Stack is the part of a plumbing system that connects interior plumbing to the sewage system and vents gases out of a home or building. In a soil stack system, the pipe runs vertically from below the building to a vent on the roof. Soil stacks usually have two sections: one section that exits directly into the sewer line running parallel to the house, and another section that has vents allowing methane gas produced by decomposing organic matter to escape. Soil stacks typically have two vents, one that exits from the top of the soil stack and another which exits from a vent line running parallel to the soil stack.
Incoming Soil Stack
The first section is an incoming soil stack: it carries drain water and sewage away from sinks, showers, and toilets inside a building before emptying directly into the sewer main below ground level. Soil stacks are usually 4 inches in diameter or larger. The plumbing code requires at least one 2-inch diameter vent on this section of the stack for each floor above the basement if not more than 3 stories high (see Soil Stack Venting). Any fixtures such as kitchen sinks or lavatories must be indirectly vented (see Soil Stack Venting ). This pile of pipes that exits vertically from the house connects with a stack vent at least once for every story in the building. Soil stacks may also be found on commercial buildings and larger structures where more than one floor may have fixtures requiring drainage. Soil stack vents are not required to be interconnected with the vents of other soil stacks but are typically installed this way to minimize turbulence or flow resistance between two soil stack vents. Soil Stack Vents
Underground Soil Stack
Underground, extended Soil Stacks carry drain water and sewage away from upper-story bathroom fixtures before emptying into an underground system approximately below ground level. They have an approximately 2 inch diameter opening which releases built up gases which can periodically cause Soil Stacks to “Burp” or Soil Stack Vents are required on these Soil Stacks. Soil stack vents are not required to be interconnected with the vents of other soil stacks but are typically installed this way to minimize turbulence or flow resistance between two soil stack vents.