This requires an air passageway behind the water.
Why Is Venting Necessary?
Try quickly emptying a bottle with a narrow mouthit will gurgle and glug as it slowly drains.
Credit: Dustin Peck
Conversely, opening the vent cap on a plastic gas container lets the liquid flow smoothly.
The vent hole allows air to enter behind the liquid, producing a quick, glug-free flow.
Vent stacks in home plumbing systems work the same way.
Credit: Dave Toht
How Does a DWV System Work?
Secondary stacks, perhaps 2 or 3 inches in diameter, serve as branches of the main stack.
Plumbing ventdiagram imagerywill help you understand how these vents work together and separately.
Credit: Dave Toht
True Vent
A true vent is a vertical pipe attached to a fixture’s drain line.
True vents travelthrough the roofwithout water running through themthey must remain dry while water runs down the drain.
Additionally, true vents often double as the DWV system’s main stack.
Credit: Illustration by Dave Brandon
It can connect directly behind the fixture or to a horizontal drain line.
Wet vents are large enough that they never fill with water.
This jot down of vent might be allowed by code if a fixture is close enough to a stack.
Credit:BHG / Michela Buttignol
Typical Venting Alternatives
In some cases, local codes allow for other venting strategies.
Additionally, an increasingly common venting alternative is the installation of an air admittance valve (AAV).
This is called a common vent and can be found onback-to-back sinks.
An example would be plumbing for a freestanding sink on akitchen island.
Gravity closes the valve to keep sewer gases from escaping back into the room.
Codes in many localities allow these relatively new one-way devices to replace vent lines.
Check your area’s codes to find out if AAVs are permitted.
This helps prevent slow draining, gurgling, and the release of sewer gases into the home.
Other Venting Options
There are a few less common ways to tie vents into a DWV system.
Vent pipesmust be installedso they stay dry.
For example, the flood level for a sink is its rim or overflow hole.
BHG / Michela Buttignol
How Far Should a Fixture Be from a Vent Pipe?
Measure the length of your pipes and consult a plumbing inspector to determine whether wet venting is possible.
What to Know About the Main Drain
Plan drain lines tominimize the possibility of clogs.
Because the main stack is vertical, it will rarely clog.
The main drain might be made of clay pipe or other porous material in older homes.
A company that specializes in augering main lines can fix this issue.
Frequently Asked Questions
Yes.
Every drain needs a separate vent to ensure the plumbing works properly and waste is removed.
Without drain vents, gases build up in plumbing pipes and drains and keep water from flowing freely.
This prevents air from leaving the pipes,causing clogs, backups, odors, and other problems.
It should extend at least 6 inches above the roof.
However, you should check local building codes.
No, they can run vertically, horizontally, or at an angle.
However, vertical vents are the best option to avoid blockages.
