How Plumbing Works in an Apartment Building

apartment building

The plumbing in a single-family residential home is relatively straightforward, as the system supplies one household. However, the plumbing network becomes slightly more complex with an apartment building. Issues with one dwelling can spiral and cause problems with others, as many apartment buildings share a common line. 

This article explains how an apartment building’s plumbing system works, so continue reading to learn more!

Types Of Apartment Buildings

In the plumbing world, apartment buildings belong in one of two categories: multiple dwelling or multiple story. Each system works differently based on the characteristics of the building, as certain features restrict the plumbing system. 

Multiple Dwelling Systems

A multiple-dwelling apartment building isn’t tall enough to be considered a multi-story dwelling, so it’s classified as a multiple dwelling. These systems may include duplexes, triplexes, and fourplexes, which feature several homes in one system. The houses may be stacked atop each other, but they might also sit side-by-side and share a wall. 

For the most part, multiple-dwelling plumbing systems mirror the system layout found in a single-family residential home. The only difference lies in the extra pipes branching into each unit to supply water. 

Besides the extra pipes, the system’s fundamentals are nearly identical. The water enters each unit via a supply pipe pulling from the municipal supply, then works its way through the home through various pipes, faucets, and valves to areas of demand. 

These systems often feature hot and cold supply lines at key points throughout the home, including kitchens and bathrooms. In addition, these plumbing systems usually feature existing water hookups for essential appliances, like washers, dishwashers, and disposers. 

These systems usually feature a drain-waste-vent (DWV) system, which escorts wastewater from each unit. These systems have various vents that allow air to enter the pipes, ensuring pressure within the system remains in range. The vents enable wastewater to flow freely through the system, preventing the formation of a vacuum that would halt the progress of sewage out of the residence. 

Multi-Story Systems

The towering apartment buildings, packed with dozens of units, often found in bustling cities, are considered multi-story systems. Given the height of these buildings, a typical plumbing system standard in a single-family residential house wouldn’t work. So, to ensure tenants in each unit have an adequate water supply, the system must address a few critical issues. 


Pressure issues are one of the most difficult challenges facing multi-story apartment buildings. Gravity isn’t working in favor of the system, especially for tenants residing on the upper floors of the building. So, to address this issue, many buildings use one of three designs. 

Some buildings incorporate gravity-based roof tanks, which bring the natural force of gravity in favor of the system. Pumps pull water from storage tanks on the ground floor or basement. Once the water reaches the roof tank, gravity aids in moving it down through the building to each unit. 

On the other hand, some buildings feature an array of booster pumps. These pumps incorporate the pressure necessary to move the water from the storage tanks or municipal water supply to units throughout the building. They add to the system’s existing pressure, ensuring it remains high enough to escort water to every unit of the building. 

Lastly, some buildings incorporate hydro-pneumatic storage tanks. These tanks store water from the municipal water supply or storage tanks in the building. Once the water is in the hydro-pneumatic storage tank, air pressure aids in moving the water to the areas of demand.


Another issue that plagues multi-story apartment buildings is drainage. The system needs adequate drainage to avoid widespread plumbing issues, so these buildings can feature multiple kinds of drainage systems, including branch lines, vertical stacks, and horizontal underground lines. 

The vertical stacks extend from the ground floor or basement of the building to the roof and include drainage stacks, soil stacks, and waste stacks. The vent or drainage stacks ensure plenty of air in the system to allow proper airflow, while the soil stacks escort water from various fixtures like urinals and toilets. The wastewater stacks move greywater from “clean water fixtures,” including showers and sinks. 

The branch lines in the system create a connection point between each vertical stack and the units throughout the building. This ensures wastewater from each unit has somewhere to go, as they transport the water to the correct stack for disposal. 

After moving through the branch lines, wastewater ends up in the horizontal lines. These lines extend beneath the building and employ the force of gravity to escort wastewater from the apartment building to the municipal waste system.

The size of the building determines the type of system design, as larger buildings usually feature two-pipe systems, while their smaller comrades typically have one-pipe systems. In a single-pipe system, wastewater and solid wastes are moved out of the apartment through one pipe. With a two-pipe system, liquids move through one pipe, and solids move through the other. 

Control Valves, Heaters, And Water Meters

Control valves and water meters are other essential parts of apartment plumbing systems. Control valves help lower the chances of cross-contamination and enable easy control of water flow to the unit without leaving the building. Water meters allow the water supplier to monitor water consumption from each unit instead of the whole building.

Lastly, many multi-story apartment buildings feature in-unit water heaters to ensure each tenant receives plenty of hot water as needed. 

Are Apartment Drains connected?

The network of vertical stacks, horizontal pipes, and branch lines in a multi-story apartment building creates a connected network between apartment units. However, while the systems ultimately connect at some point, most apartments usually only share a few pipes or a particular section of pipes. 

More often than not, the pipes you see in your unit and those directly surrounding it are solely yours. That said, some buildings have 2-3 units sharing a few pipes or a section of pipes. 

Do Plumbing Problems In One Unit Affect The Whole Building?

The extent of ripple effects from plumbing problems in one unit depends on the plumbing setup. For example, if one unit has a clogged drain or toilet and shares a common line with others, it could cause issues for units on the same line. This is a common affliction for plumbing systems in apartment buildings, as problems in one apartment can affect others nearby. 

Frozen pipes are another potential issue that could affect the water supply to all apartments in the building. If the lines are connected, and there’s no insulation protecting the common line, it could freeze (in cold climates). In some cases, the frozen blockage can create a clog, ceasing water flow to the entire building. 

Plumbing Issues Causing A Commotion? Ace Solves It All Can Help! 

Addressing plumbing issues in an apartment building is different than in a single-family residential home, potentially making problems trickier to understand. It’s essential to understand the system and how it works, including how it connects with each unit, before attempting to tackle an issue. Sometimes, it’s best to consult an experienced plumber for assistance. 

So, if you’re in dire need of an experienced plumber, Ace Solves It All Can Help! Call us at (407) 499-8006 or fill out a contact form to schedule a service appointment today!

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