What is a plumbing stack and why is it important to your home?

What is a plumbing stack and why is it important to your home?



Your plumbing system is much more extensive than the pipes under your sink and the drains in your bathroom. A network of pipes runs like veins through your home, and at the very heart lies your plumbing stack, which supports these pipes and keeps the water flowing quickly.

A plumbing stack is a critical component of any home’s plumbing system, and understanding the common problems with vent stacks and when to replace them will help you make the best and most cost-efficient decisions for your home.

This article outlines what plumbing stacks are, how they work, common issues with them and the estimated cost of repairs. Keep reading to learn more!


What is a plumbing stack?

A plumbing stack, also called a plumbing vent or a vent stack, is a long, vertical pipe extending out of your roof that directs wastewater from all the fixtures in your home to a municipal or private sewer system. The name “stack” comes from the architectural concept of a vertical column of straight pipe that rises from floor to ceiling.

The plumbing stack is the central hub from where other plumbing fixtures branch out. Not only does it help regulate the air pressure inside your pipes to keep water flowing smoothly, but it also filters out dangerous gases and allows fresh air into your plumbing system.

There can be different types of plumbing stacks and vents, and understanding these types will help you choose the one best suited for you, if you’re in the market for a new plumbing stack.

Types of plumbing stacks

The most common material options for a plumbing stack are cast iron or PVC. Understand the differences between these two types for a better idea of what problems to expect and which is better for you.

Cast-iron plumbing stacks have been used for centuries and are still used today. While these pipes are incredibly durable, they’re prone to catching rust, so you have to be very careful about good maintenance. The pipe should be repaired or replaced as soon as you see the first signs of rust to prevent more extensive damage.

In contrast, PVC pipes are made from plastic. They’re less durable compared to cast iron, but they don’t run the risk of catching rust, which makes the maintenance process much easier.

Refer to the table below for a detailed comparison of these two types of plumbing stacks.

 Factor  Cast-Iron Pipes  PVC Pipes
 Adjustability  Fittings are easily readjustable during home remodels, etc.  If changes are needed after installation, parts of the fittings must be replaced.
 Price  Costs more.  Costs around 50% less than cast-iron pipes.
 Heat resistance  Extremely heat- and fire-resistant.  PVC pipes are heat-resistant but risk melting in house fires.
 Flexibility  Cast-iron pipes are brittle and can break with some force.  PVC pipes are more flexible, so they are less likely to break.
 Pipe performance  The walls of iron pipes are rougher, causing more water friction and reducing pipe performance.  The walls of PVC pipes are smooth, causing less friction and a more constant water flow rate, giving better pipe performance.

In addition to these types of plumbing stacks, you also have several vent options to choose from: 

  • True vents: This vent pipe runs through the plumbing stack on the roof, and no water runs through it. This is the most commonly used vent system.
  • Common vents: A common vent connects two different drainage systems before linking up to the true vent.
  • Auxilary vents: This vent connects to the main drain line somewhere around the plumbing fixture, then it runs up to connect to the main vent.
  • Loop vents: These are used for free-standing sinks that don’t have wall support, so the vent forms a loop below the sink and then drops under the floor to connect horizontally to the vent stack.

You should be aware of these various types of plumbing stacks and vents. But to detect problems with your plumbing stack easily, it's essential to understand how it works.


What does a plumbing stack do?

The critical functions of a plumbing stack or a drain waste vent (DWV) include:

  • Carrying your wastewater and sewage to an underground sewage system.
  • Preventing harmful gases from entering your waste pipes.
  • Allowing fresh air to enter your plumbing system.
  • Controlling the air pressure in your plumbing system to facilitate the easy flow of water.

You might already be aware that drainpipes drain the wastewater from your home into a sewage system, and a supply line allows fresh water to flow through your taps. 

A plumbing stack is a little different because it doesn’t carry water. Instead, it regulates air pressure within your pipes to allow this water to flow smoothly and prevent the buildup of toxic gases in your pipes.

But if plumbing stacks neither directly drain nor supply water from or into your home, how essential is it to have one?


Do you need a plumbing stack in your home?

The average American uses around 82 gallons of water a day. That’s a lot of water going through your plumbing system! Naturally, with so much waste flowing through the pipes, gases build up in your sewer pipes, and the vents in your house help to release these gases. However, if there are blockages in your vent stack, they can cause the sewer gases to flow back into your home, which can lead to health problems for you and your family. 

Plumbing stacks are important because they direct water flow from fixtures toward the sewer system. That way, wastewater doesn’t get backed up and flood your home. Without them, homeowners would have to rely on drain stacks and horizontal pipes that divert wastewater from fixtures and direct it toward the public sewer line. These drain stacks are much less efficient than vertical plumbing stacks because horizontal pipes don’t carry water as quickly as vertical pipes. If every fixture drain in your home were to run at once, drain stacks wouldn’t be able to handle the drain volume, leading to plumbing problems.

If your plumbing stack is clogged and water backs up, the unpleasant plumbing odors and sewage smells can give you headaches, and you might experience nausea and drowsiness.

In addition, without a proper plumbing stack and vent, your drainage system can have negative pressure buildup, meaning water won’t flow out of your home at all without a proper cleanout.

So, a properly working plumbing stack is essential to maintain a hygienic environment in your home.

If you’re currently experiencing drainage problems, a blocked vent may be the cause. Read on to know common plumbing stack problems and how to identify them.


Main issues with plumbing stacks

The two most common issues with plumbing stacks are broken collars and clogging.

A collar is the strip of aluminum that wraps around the base of your vent stack on your roof, with a rubber boot over the aluminum. 

Due to exposure to direct sun rays, the rubber can deteriorate or melt over time, creating a leak in your roof where water can get into your walls, causing mold. For this reason, you should frequently inspect your home and plumbing to prevent such damage. If you notice water pooling around the base of your vent stack, look into hiring a quality plumber to fix your broken collar.

Another common problem that American households face is clogged plumbing stacks. Because these vents are located on the roof, dirt and debris can easily accumulate, along with other things like bird's nests, leaves or dead animals in the pipe.

A clogged vent stack will create a buildup of negative pressure in your home, which leads to slow drains or no drainage. You may even hear gurgling sounds in your pipes. 

A clogged plumbing stack is tricky because it can appear to be a clog in your fixtures. The key to correctly diagnosing the cause of the issue is noticing if this happens with several drains in your house. If only one drain is acting up, it’s probably a problem with that fixture, but if several drain slower than usual, it’s likely a problem with the plumbing stack. In that case, you will need to hire a professional plumber to assess the sitwwwion.

Apart from this, a new plumbing stack can experience issues if it’s too narrow or too long. If the waste stack is too narrow, wastewater will back up into your home and cause clogs and odors. If the stack is too long, wastewater will flow slowly through it and take longer to reach the sewer system. Sometimes, a plumbing stack can also become sloped or curved at the end, signifying it needs to be replaced.

But how do you know if your plumbing stack has damage?



6 warning signs that your plumbing stack needs to be replaced

If you haven’t had your plumbing system checked in a few years, here are a few warning signs that your plumbing stack might need replacement:

  • Slow drainage: If your kitchen sinks or toilets are draining slowly and standard unclogging procedures aren’t helping, the problem is likely a clog in your plumbing stack.
  • Discolored water: If you see brown, orange or oddly colored water flowing through your toilet, it might indicate that your cast-iron plumbing stack is rusted and needs replacement.
  • Wet spots on walls: If you see that your internal walls around the stack appear to be damp, your plumbing stack could be leaking. Even a minor leak in the pipe could lead to a pipe burst, so call a professional immediately.
  • Foul odor: If you notice a terrible smell in your home, it could indicate a leaking plumbing stack. Normally, your plumbing should be airtight, and all toxic gases should be released through the stack vent. But in the event of leaks, these toxic gases can create a foul odor in your home.
  • Mold: A leak in your plumbing stack and wet spots on walls can lead to mold formation, weakening your walls.
  • Barnacles or rust spots: If you notice any rust on or around your plumbing stack, you should call a plumber to assess the sitwwwion.

If you notice these warning signs and suspect that your plumbing stack might need to be replaced, take action sooner rather than later to minimize damage and expense. This is because, in addition to being unhygienic and inconvenient, residential plumbing stack repairs and replacements can be very costly.

How much does it cost to replace a plumbing stack?

Depending on the plumbing stack you have and what the issue is, the repairs can vary in complexity and cost. 

The cost of replacing a plumbing stack depends on where it’s placed in the home and how big of a stack you need. Plumbing stacks are often placed in the attic, basement or wall. The cost also depends on the stack's size and the materials used to build it, the labor charges, and any other unexpected costs. On average, expect to pay between $1,500 and $4,000 to replace your plumbing stack, according to HomeAdvisor.


Costly plumbing system repairs are covered under a Cinch warranty

A plumbing stack is a critical component of any home’s plumbing system. Without it, your plumbing system can’t work as efficiently as it should. It’s a good idea to regularly inspect your home and appliances to spot any developing problems and get them fixed rather than pay for costly repairs after more extensive damage.

To avoid expensive plumbing repair costs, sign up for Cinch’s Built-in Systems plan, which covers plumbing system repairs. In addition, this plan also gives you rust and corrosion coverage, protection for unknown pre-existing damages, and discounts on new devices. If you want to know more, you can get a custom quote for your home here.


Tired of slow drainage? Your plumbing stack may be the problem. Read on to learn more about what a plumbing stack is and why it’s important to your home.

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