How Plumbing Vent Pipe Works in Your Home

The vent pipe system is composed of pipes connected to the drain lines and waste lines that exhaust sewer gases through the roof. This system allows wastes from toilets and wastewater from sinks and showers to flow freely.

The drain and waste lines have a slight slope downward and move by gravity. It starts from the fixture and going to the sewer line or septic tank.

The sizes of waste pipes are large to avoid the probability of blockages. For toilets, the usual size is 4 inches. For drain pipes, shower drains are usually sized at 2 inches, while sinks and bathtubs range from 1 1/4 to 2 inches in diameter.

The materials of the waste and drain pipes are commonly made of PVC or plastic, cast iron, galvanized iron or copper. Some of the very old homes might have used lead piping material.

For the drain and waste line to function properly and safely, they must be connected to a vent line that allows sewer gases to go out through the roof. These vents may interconnect and end up going towards one larger soil stack that penetrates the roof. This is okay as long as there is no drain that connects directly at the connection point.

Sometimes, many vent pipes pass through the roof. What’s important is that the correct flashing is used to protect the house from roof leakages. Local code requirements may vary, but the vent pipe extends from the roof by around 2 feet so it doesn’t gets covered when it snows.

It is also important for waste lines to have cleanouts at necessary intervals and accessible areas. A cleanout is a y-shaped fitting that juts out through the floor and has a cover. Should the drain malfunction, a cleanout allows for the plumber to repair with the use of a drain snake.

In order to prevent the waste gases and odors from going into the house, traps are installed near drains. A trap is a curved pipe that allows water to stay, providing a blockage against odors. Drains that pass through the wall have what’s called a “P-trap”, like what you see in the kitchen sin. Drains that go through the floor have an “S-trap”, like in the toilet and floor drains.

Compared to drain and waste pipe repairs, vent pipe repairs are rarely necessary. When it happens, the problem is most probably clogging and corrosion of the pipes. This results to odor getting into the house. You will have to find the source of the problem.

One way to do so is called the Peppermint Test. This is done by sealing of the pipe lines and inducing peppermint oil into the vent pipe system. Peppermint has a strong smell and it will let you know right away where the source of the problem is located and have it repaired.

The cost for vent pipe repairs depend on the scope and materials needed. To know what needs to be done and how much it would cost, ask a professional plumber.