What the vent does and how it gets blocked
A plumbing vent is a pipe that runs from your drain lines up through the roof. It lets air in behind moving water, so drains empty smoothly and the water seal in each trap stays put. A blocked vent starves the system of air, and the first signs are gurgling, slow drains and a sewer smell.
The usual culprits are a bird or wasp nest, leaves and debris dropped into the open pipe, a cracked or crushed section inside a wall, or a vent that was cut off or capped during a remodel. Most vent trouble starts at the roof end, where the pipe is exposed to everything that falls on it.
Gurgling, slow drains and smells: the vent clues
One slow sink usually means a local clog. A vent problem tends to show up in more than one place, or in sounds rather than standing water.
Gurgling after a flush
Air that cannot come in from the roof gets pulled through the nearest trap instead, so a tub or sink burbles when the toilet flushes.
Slow drains across the house
Water drags in a pipe when no air follows it, much like a bottle held upside down with the cap on.
A sewer smell in the bathroom
If the vacuum pulls a trap dry, sewer gas comes up through the drain. The smell is stronger after a big flush.
A toilet that flushes weakly or glugs
A bowl that takes a long time to settle and glugs while it does is a classic vent clue, as long as the main line is clear.
Checks you can make from the ground
None of these needs a ladder. Run them in order and note what changes.
Test one fixture at a time
Run the sink, then the tub, then flush the toilet. Write down which ones gurgle and which are slow.
Listen at a tub or shower drain
If a toilet flush makes the tub drain burp, air is being pulled from the wrong place.
Look at the roof from the yard
Walk around the house and find the vent pipes, usually a plain round pipe poking through the shingles. Binoculars help you spot a nest or a missing cap.
Check the main line cleanout
If water also rises in a floor drain, the problem may be a clogged main line and not a vent. That is a different repair.
Suwanee note: the 6-inch vent rule and the city permit
Georgia's state minimum plumbing code is the International Plumbing Code with Georgia amendments, adopted by the Department of Community Affairs. One amendment in the DCA packet says open vent pipes that extend through a roof shall be terminated not less than 6 inches above the roof. If your vent looks very short on a low-slope roof or after a re-roof, ask a plumber to check the height.
That one line is the only vent rule we cite. Venting also has rules about pipe size, slope and distance that are not covered here, and they depend on the code edition in force for your job. Ask your installer which rules apply to your house instead of relying on a number you read online.
The City of Suwanee permit page says changes to plumbing systems need a building permit, and it lists 770-945-8996 for permits and inspections. Adding a vent line, moving a fixture or re-routing a stack counts as a plumbing change, so call the city before work starts.
What a homeowner can do and what belongs to a plumber
Keep your feet on the ground unless you are comfortable on a roof. A vent opening is usually the highest, most exposed point of the house.
Safe for you to do
- Find the vent pipes from the yard and photograph the tops.
- Note which fixtures gurgle, and when.
- Check the attic or a basement wall for a vent pipe that has been capped or cut off.
Better left to a plumber
- Climbing onto the roof to clear or cap a vent.
- Running cable or a camera down the vent line.
- Repairing a cracked pipe, flashing or boot around the vent.
- Adding an air admittance valve or a new vent line.
Roof work is where people get hurt
A roof can be wet, steep or slick with pollen, and a fall from even a single story causes serious injury. Do not climb on a wet roof, do not climb alone, and stay clear of power lines at the service drop. If a vent is out of reach from a ladder, call someone with the right fall protection.
If the smell inside the house is like rotten eggs, do not assume it is sewer gas. Natural gas smells like rotten eggs too. Leave the building, then call the gas utility, for most homes Atlanta Gas Light at 877.427.4321, or 911, before you call a plumber.
What a plumber actually does about a blocked vent
The first job is to separate a vent problem from a drain clog. A plumber runs water in several fixtures and listens, then looks at the roof end of the pipe. If the line is blocked at the top, the fix may be as simple as clearing the nest and fitting a cap suited to the pipe.
A cable or a small camera can be fed down the vent from the roof to find a blockage inside the wall. A cracked or crushed section is a repair, not a cleaning, and may mean opening the wall. If the camera shows the vent clear, the cause is probably a clogged main line, and sewer line cleaning or drain cleaning is the next step.
Some older additions and remodels use an air admittance valve, a one-way valve that lets air in without a roof pipe. Whether one is acceptable for your job is a code question, so ask the plumber and the city. Homeowners in Duluth and Lawrenceville face the same questions when a remodel adds a bathroom.
The International Plumbing Code with Georgia amendments is the state minimum standard that covers drain, waste and vent systems. According to the City of Suwanee's building permits page, changes to plumbing need a city permit.
Plumbing vent questions
Yes. Water leaving a pipe needs air behind it, and a blocked vent removes that supply. Drains in more than one fixture slow down, often with gurgling.
A clogged main line tends to cause water to rise in the lowest drain, such as a floor drain or tub. A vent problem tends to cause gurgling and smells first. A plumber can tell for sure with a camera.
Looking at it from the yard is fine. Climbing onto the roof is where the risk sits, so call a plumber if the vent is not reachable from a ladder.
The city's permit page lists changes to plumbing systems as needing a building permit. Call 770-945-8996 before adding or moving a vent line, and ask your plumber whether simple clearing counts.
A Georgia amendment says an open vent pipe through a roof shall end not less than 6 inches above the roof. Other venting rules exist, so ask your plumber what applies to your house.