Don’t be left with an unreliable system during a significant rain event by not specifying no-hub fitting restraints.
by Jim LeStage, CSI, CDT
Looking at the geographic location or climate of your next job is important in determining how much heavy rainfall could hit the next storm drain system you design. This is often an indicator of the amount of thrust force the system is likely to undergo. If the piping system isn’t properly supported with durable restraints like no-hub fitting restraints, it could lead to pipe system failure and potentially disastrous building damage.
Despite the possible catastrophic outcomes, no-hub fitting restraints aren’t included in plumbing specifications as often as they should be. Let’s dive into a few reasons why that is and why plumbing engineers should add no-hub fitting restraints to their specifications to provide the best possible outcome and protect their company’s reputation.
Why No-Hub Fitting Restraints Are Often Not Installed and the Ramifications
In 2009, the International Plumbing Code addressed the need to install no-hub fitting restraints but didn’t specify exactly how the pipe and fitting needed to be restrained. Many installers will get creative in their use of readily available materials to make their own pipe restraints out in the field. This do-it-yourself (DIY) approach is untested and is often limited to the installer’s imagination and ability to jerry-rig a restraint device. Reasons for choosing the DIY method vary.
Too Labor-Intensive and Costly
On large projects, outfitting the entire storm, waste, or vent system as prescribed by both the International Plumbing Code and the Cast Iron Soil Pipe Institute can be a labor-intensive and costly endeavor. It’s no surprise that unless it is specified as a requirement of the job, chances are it will be overlooked or omitted.
However, when you look at it closely, DIY is much more labor-intensive. It can take anywhere from 30 minutes to an hour to measure, cut, and fabricate a field-devised system. If a plumber is being paid $60 to $70 an hour and they’re taking the time to fabricate a DIY restraint system for each coupling on a 20-floor building, the labor cost for this approach can be excessive.
Many Inspectors Are Unaware of the Code
Shockingly, many inspectors are unaware of the requirements for restraints, and a lot of plumbers or installers are aware they should be installing restraints but will wait to see if the inspector will notice.
Before the issue was addressed in the plumbing code, the only time some plumbers shackled the pipe and fitting together was when they were testing the system. However, once the system passed the test and the inspector was satisfied with the installation, they would remove the shackling and assume the system was complete. Unfortunately, even today many plumbers and installers still take this approach, but the only thing worse than a field-devised restraint is no restraint at all.
When to Specify the Use of No-Hub Fitting Restraints
As you design a plumbing system, it’s important to consider the force of substantial rainwater or sanitary liquids flowing down a pipe. Without proper support, this force can cause significant damage if the pipe is not reinforced with no-hub fitting restraints.
Here are the top reasons to include specifications of no-hub fitting restraints:
- Thrust forces greater than 10 feet of head pressure: All pipes and fittings on DWV systems must be tested to ensure they do not leak. One of the most common methods of testing is with a 10-foot column of water above the lowest point of the system. Since DWV systems are open-gravity drainage systems, they are not designed or intended to hold pressure. Occasionally, thrust forces greater than a 10-foot water column equivalent may be placed on the system due to high flow during rain events. If the system will likely be subjected to thrust forces greater than the 10-foot water column equivalent, then thrust restraints should be included in the design.
- Installing a no-hub coupling: It’s also important to note that no-hub couplings are not restraints on their own—even with only 10 feet of head pressure. Couplings are a weak point in the system. Without something to restrain the pipe and fitting against thrust, a no-hub coupling will not prevent pipe and fitting separation at thrust forces greater than the 10-foot head equivalent.
- Installing a large pipe size: If a cast iron soil pipe is 5 inches in diameter or larger, specify restraints. The larger the diameter of the pipe, the more thrust force the connections will endure during a heavy rainfall event.
- Building two stories or more: While pipe restraints may not be necessary on single-story projects, you need to consider them for any project that is two stories or more, where the potential to exceed that 10-foot head thrust exists.
How Engineering Firms Can Mitigate Liability
After taking the time and effort to design the plumbing system for a major build, you could still be left with an unreliable system during a significant rain event if you don’t specifically specify engineered no-hub fitting restraints. When you take into consideration the amount of liability you assume by allowing untested, non-standardized systems, the potential costs are even higher.
There are two key things that engineering firms can do to mitigate their liability in this area:
- Require the use of engineered solutions. Put engineered no-hub pipe fittings into your specs, and specifically disallow the use of field-devised restraint solutions.
- Do your due diligence on the rest of the system. Look at the system’s design requirements and what stressors the system is likely to be subjected to and plan accordingly.
It may be time to consider adding no-hub fitting restraints to your specification sheets. It’s a proven way to protect the building from damage and protect your company’s reputation.
About the Author
Jim LeStage, CSI, CDT, is the Specification Sales Manager at RWC—a market leader and manufacturer of water control systems and plumbing solutions for residential, commercial, and industrial applications. To learn more about RWC and its family of brands, visit rwc.com. You can read Jim’s previous article on no-hub fitting restraints here: aspe.org/pipeline/four-common-misconceptions-about-specifying-no-hub-fitting-restraints.
The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.
