Frequently Asked Questions (FAQs)

While we can’t diagnose your plumbing problem without a look at your specific pipes, gurgling (or bubbling) sounds are a frequent sign of restricted lines in single-stack systems. In a mid- to high-rise building with a single-stack drain, waste and vent system, you may be hearing signs that the piping needs to be cleaned or replaced.

What might be causing this? Here are a few common sources of issues with single-stack DWV systems:

• Improper maintenance and repairs. Single-stack systems require more specialized maintenance than conventional piping. Standard snaking techniques aren’t designed for these horizontal lines and can damage the fittings if applied incorrectly—so it’s important to work with technicians who know the system. That expertise has become less common as these systems age, which means buildings sometimes defer maintenance longer than they should simply because it’s harder for them to find the right contractor.

• Installation issues. Particularly when single-stacks were gaining traction in the US in the late 1970s, contractors didn’t always understand how to properly install these systems. For example, they may have skipped installing deaerators, which are an essential component. They may have also used single-stack design for functions it’s less suited for, such as dealing with the sudsy discharge from washing machines. Installation flaws can lead to back-ups and infrastructure failures well ahead of the typical timelines.

• Age. Like any plumbing system, single-stack DWV piping deteriorates over time. In many cases, this infrastructure may have reached the end of its useful life (approximately 50 years in multifamily properties), so it may be showing its age with blockages and other issues.

A few signs that something might be going wrong with your single-stack DWV piping include:

• Slow or stopped drains across multiple units. Slow or non-flowing drains appearing in multiple locations simultaneously is a recognized indicator of single-stack infrastructure trouble.

• Gurgling sounds. A gurgling or bubbling sound coming from plumbing can indicate that the pipe is clogged or under pressure. You may even see bubbling in your toilet water.

• Water stains, dampness, and mold. Signs of leaks in your single-stack system include water stains on walls or ceilings, musty odors, and dampness around plumbing fixtures.

• Discolored water. If you’ve got a cast iron single-stack system, brown or yellow water is one of the most visible signs that pipes have become corroded or rusted internally.

A single-stack drain, waste and vent piping system uses one main vertical stack instead of separate drain and vent stacks. It’s often called Sovent® after one of the more prominent brands in the US multifamily market. Aerators and deaerators allow air and waste to move through the single stack, maintaining proper drainage while protecting the pipes by controlling pressure. While less common than conventional two-stack systems, single-stack piping can be found in mid- to high-rise properties, particularly those built in the 1970s and 1980s. Designers or developers may choose it because the infrastructure requires less space and it costs less than conventional systems to install (i.e., lower material and labor costs).

When selecting a contractor to replace or install single-stack DWV piping, you’ll first want to make sure they’re experienced with properly installing the special features of single-stack piping, such as aerators and deaerators. Then, look for pipe replacement experts who are accustomed to working on large-scale projects in occupied multifamily properties of your size. SageWater, for example, can provide a turnkey, design-build solution that streamlines your process by including engineering design and self-performing the construction services.

Whatever solution your designer proposes, be sure to ask them to explain their reasoning. In many cases—like when there’s limited space—replacing your existing infrastructure with another single-stack DWV system makes the most sense. (It can also cost less.) There may be times, however, when best practice is to replace your single-stack system with a more conventional two-stack drain and vent system. Your designer’s answers will help you gauge whether they genuinely understand single-stack systems, including the benefits, limitations, and the conditions under which a hybrid or conventional solution is warranted.