The plumbing vents are important to ensure that your whole plumbing system functions properly. Of all the systems in the home, plumbing is one of the worst if something goes wrong—no one wants sewer smells or worse, sewer water, filtering out of the pipes and flowing through the house.
Where the main plumbing vent (vent stack) terminates (stack vent) is vital because it is responsible for the control of pressures and release of gases from the plumbing system that keep it functioning smoothly. As such, there are specific requirements for this part of the plumbing.
|Plumbing Vent Termination by Topic||IRC Coordinates||Code Summary|
|External venting||P3102.1||At least one vent stack must terminate outside|
|Possible location of stack vent||P3103.1|
|Roof, sidewall, or soffit|
|Distance from openings||P3103.5||Minimum 4′ above, 3′ below, and 10′ to the side of openings into the house|
|Distance above roof (roof vents)||P3103.1.1|
|6″ above roof or snow line (whichever is higher)|
7′ above recreational roof space
2″ if the roof is covered (must be protected against animals)
|Sidewall venting||P3103.1.4||10′ from lot lines|
10′ above highest topographical point in a 10′ radius
Protected against animals
Not on walls with overhang soffit vents
|Frost considerations||P3103.2||Minimum 3″ diameter if the area is below or at 0 ℉ for 97.5% of the year|
|Protecting the opening around the vent||P3103.3||Flashing around roof vents|
Caulk around sidewall/soffit vents
Where to Find the Requirements
The regulations and requirements for plumbing vent termination can be found in the International Residential Code (IRC). These are the generalized building codes used for one- and two-family dwelling units, and contravening the code is against the law.
The IRC is used in the majority of the United States (only Wisconsin does not adopt this code) as well as other North American territories, such as Guam and Puerto Rico.
While the IRC is the general standard, each state and territory is permitted to make certain adaptations and additions that will better suit the needs and climate of that area. These local codes will take precedence over the IRC.
For this reason, it is important to consult your local codes. These can be found on UpCodes but should also be available from government or local officials’ offices. If you hire a contractor, they will be in charge of ensuring code compliance.
For the sake of this article, however, we will simply look at the IRC as it is the most generalized and it serves as the base code for the local ones.
Only One Vent Requires Outdoor Termination
In Section P3102.1, it states that:
“The vent system serving each building drain shall have not less than one vent pipe that extended to the outdoors.”
Those that don’t extend outside must be terminally fitted with an air admittance valve (AAV).
As mentioned, the plumbing vent is supposed to control the pressures inside the plumbing system and allow the sewer gases to escape safely.
AAVs allow for an inflow of air that will balance the air pressure (specifically the negative air pressure) as well as prevent the siphonage of the water trap when negative air pressure builds up.
However, it is designed to prevent any gases originating in the plumbing system from escaping out of the pipes. As the AAVs are for pipes that terminate indoors, such a release of gas would be very unpleasant and even harmful to health.
The plumbing vent that terminated outdoors is designed to allow the free movement of air both in and out of the plumbing system. So, it helps to alleviate negative pressure but it also serves as an escape route for sewer gas (positive pressure).
The code says “not less than one”, which means that if you have more than one stack vent, then you are still fine. It just means that you will have more holes through your house.
Where Can a Plumbing Vent Terminate?
When we talk about the terminating plumbing vent, we are specifically talking about the stack vent, which is the part of the main vent stack above the last drain and which extends to the outside.
According to Section P3103.1 of the IRC, a stack vent can be vented through the roof or sidewall. This is plainly stated.
Outside termination is important because, as mentioned, you don’t want sewer gases to be filling your home.
The main risks of sewer gas building up in your home include hydrogen sulfide poisoning and the risk of fire and explosion.
Hydrogen sulfide poisoning is common when exposed to sewer gas, and the symptoms include drowsiness, nausea, headache, and eye and lung irritation. After prolonged exposure to hydrogen sulfide, loss of consciousness and even death are possible.
Another component of sewer gas is methane. Both methane and hydrogen sulfide are extremely reactive and can cause fires or explosions.
There are further limits to the placement of the stack vent, which can also dictate if the roof, wall, or soffit is the best choice.
According to Section P3103.5 of the IRC, the termination point must be:
- Four feet or more below openings into the house. Any closer and the sewer gases can readily drift up and enter your home.
- Three feet or more above openings into the house. This is a smaller minimum distance because gases are unlikely to sink. Instead, the exhaust rises because it is often warmer than the surrounding air.
- Ten feet or more to the side of openings into the house. This is because air preferentially enters vertical openings, like a window, horizontally, so the opening’s surrounding horizontal area must be clear of termination vents.
Don’t forget that this is not only referring to openings in your own house; you need to consider your neighbors as well.
Additionally, while we most quickly think of windows and doors when talking about openings into the house, there are also things like air supply inlets/intakes for furnaces, ACs, heat pumps, and gas-powered appliances.
Roof Plumbing Vent Termination Requirements
With the requirements listed above, venting through the roof may be the easiest since it is often farthest away from openings to your home and your neighbors’ houses.
However, venting through the roof has its own set of requirements.
According to Section P3103.1.1 of the IRC, the plumbing vent must terminate at least six inches above the roof or at least six inches above the anticipated snow line, whichever height is greater.
There are some state-specific variations in the height, which you can find in our article Plumbing Vent Height Above Roof.
For regions that do not experience much snow accumulation, it is still important to have roof plumbing vents distanced from the roof to limit animal access to the vent as well as to limit accumulated rainfall from entering the vents, especially with a flat roof.
Plumbing vents don’t need to be protected from rain like bathroom or dryer exhaust vents, which is why they don’t require any kind of cap, but having a deluge running down into your house drains is not great.
Regions that do experience snow accumulation must extend their vent pipes even higher to prevent snow from blocking the vent.
Roofs Used As Open Recreational Areas
Roofs used for recreational purposes can still have the plumbing vent running through them. The difference is that the six-inch height is not sufficient in such cases.
Shorter vents will release sewer gases into the occupied area as well as prove to be a hazard for the occupants’ toes.
Luckily, the IRC takes this into account and amends the rules for roofs that are sometimes occupied.
Section P3103.1.2 of the IRC states that when a roof is used for recreation, the open stack vents must terminate at least seven feet above the roof.
This pipe will most likely be taller than you and your guests and will allow the exhaust to rise without being breathed in and, hopefully, without being smelt.
A pipe this tall is also much easier to see, so you are less likely to kick your toes.
However, a seven-foot long pipe can certainly be an eyesore and can be difficult to cover up, especially since Section P3103.4 of the IRC states that the vent terminal cannot serve another use other than a vent terminal.
In other words, you cannot use the vent terminal as a flag pole, for example, to hide the fact that a plumbing vent is on your deck.
There are still ways to conceal this vent terminal, for example, a tall room divider to block off the area but add some decor.
When Roofs Are Covered
There is one final scenario that the IRC has taken into consideration when it comes to venting the stack vent through the roof.
In Section P3103.1.3 of the IRC, it is stated that, if your plumbing vents terminate on the roof but are under some form of cover, the pipe’s termination length must be changed.
Roof covers can come in the form of a decorative shroud or some other overhanging roof element.
Because of these forms of cover, the normal termination rules cannot apply since the cover would impede the exit of sewer gases from a tall plumbing vent.
Instead, with a cover over a plumbing pipe, the requirements state that the pipes must be at least two inches above the roof surface.
Additionally, this section of the IRC states that these covers must provide protection to the pipe from rain, snow, and wind.
The same goes for a pipe with a solar panel placed above it. The panel would impede the exit of sewer gases, so a shorter vent allows for sewer gases to exit and disperse freely.
However, Section P3103.1.3 of the IRC requires that, with a cover, the opening of the pipe must be protected from birds or rodents that try to nest in it since a shorter pipe can be more easily accessed by wildlife.
This section also requires that an area equal to the area of the opening of the vent is open above the vent. In other words, the area above the vent must not be covered.
Sidewall Plumbing Vent Termination Requirements
With venting through the roof, it seems to be a lot of information to keep track of. However, with venting through a sidewall, the rules are relatively simple.
First off, Section P3103.1.4 of the IRC says that the plumbing vent must terminate at least ten feet away from any lot lines.
A lot line is where your property ends and your neighbor’s property, or some other form of property, begins. It is a legal boundary.
Venting your plumbing system in such a way that sewer gas enters your neighbor’s property, dictating how they use their land or creating an unpleasant and unhealthy living environment is not permitted, which is why the lot line rule exists.
It is specifically listed under the sidewall venting requirements because wall vents are more likely to be close to a lot line than a roof vent.
Section P3103.1.4 of the IRC also requires that the vents must terminate at least ten feet above the ground within a ten-foot radius around the highest elevation in the area.
This allows for the flow and dissipation of sewer gases to be unimpeded by the surrounding topography of the area.
For example, if the vent terminated at the bottom of a depression in the ground, the sewer gases would accumulate and be prevented from dissipating properly. This could potentially lead to someone being exposed to these gases if they were in the area.
Finally, this same section of the IRC requires that a plumbing vent must not terminate anywhere below the overhang of a roof that contains soffit vents.
If a vent was to terminate under a roof overhang containing soffit vents, the gases could enter the soffit vent, your attic, and eventually the rest of your home.
In Section P3103.2 of the IRC, it says:
“Where the 97.5-percent value for outside design temperature is 0℉ (-18°C) or less, vent extensions through a roof or wall shall be not less than 3 inches (76 mm) in diameter.”
What this means is that, if the location is below or at 0 ℉ for 97.5% of the year, the vent extensions must be a certain width (three-inch diameter) to account for the potential freezing of the pipes in these cold conditions.
Freezing of the pipes would block off the exhaust, not allowing it to exit and forcing it back into the pipes, causing pressure problems, which result in things like sewer smells from drains, backflow, noisy drains, and empty toilet bowls.
The vent only has to be this size from at least one foot inside of the thermal envelope. The thermal envelope refers to the insulating layer of your home and it can include or exclude spaces like the attic, basement, and crawlspaces.
Protecting the Hole Cut Into the House
Once the location of your piping is all settled, the hole cut into your home must also be considered.
According to Section P3103.3 of the IRC, the point at which the vent pierces the roof has to be made watertight with flashing, and the flashing used has to be approved for such use.
Watertight means that water is not able to get through any seams.
Flashing refers to thin pieces of impervious materials whose goal is to prevent water from getting into a structure.
Caulk can be used to achieve weathertightness for vent extensions in the walls and soffit.
Weathertightness means that the area is impervious to the elements, including most temperature changes, rain, snow, and wind.