Do I Need to Vent the Plumbing for a Basement Bath?

Vent Placement

• Local plumbing codes dictate exactly where plumbing vent pipes should be placed on your house’s plumbing. As a general rule, though, the vent pipes connect to the drainpipes from the bathroom downstream from the plumbing fixtures’ trap pieces. The main stack vent runs vertically, penetrating the house’s roof where it opens to the outside. If you have trees near the house, installing wire mesh or a cap piece onto the vent opening helps keep debris out without restricting airflow into and out of the pipe.

Sewer Gases

• All plumbing fixtures need to be connected to a vent pipe so sewer gases can flow outside the house. The sewer gases that build in the drainpipes can contain dangerous or even lethal gases. Exposure to these gases can in extreme cases cause people to lose consciousness or even die from asphyxiation. Sewer gases also can be explosive, meaning any spark in your house could ignite trapped gases and cause an explosion. Without a vent pipe connected to your basement bathroom’s plumbing, the sewer gases become trapped and eventually will flow into the house.

Wastewater Flow

• Vent pipes also facilitate the proper flow of water down the drainpipes. If the plumbing vent pipe becomes clogged with leaves, ice or other debris, the drains connected to the vent pipe may begin to gurgle or operate slowly. Because the vent pipes are open to the outside air, they allow new air to flow into the pipes when wastewater pushes the air in front of it down the drainpipes. Obstructions in the vent pipes lead to the wastewater not flowing down the drainpipes smoothly.

Pipe Traps

• Every plumbing fixture needs to have a pipe trap in its drain line. The trap piece is the curving section of drainpipe you find under the sinks in your house. Because of its U shape, the trap piece stays full of water, creating a barrier against the sewer gases in the drainpipes. If no vent pipe is present, the lack of fresh air flowing into the pipes would allow the water in the trap to be sucked down the pipes, and nothing stands in the way of the sewer gases flowing up and out the plumbing fixtures’ drain openings.