What Freeze Protection Is Needed in an Unheated, Open Parking Garage?

As it starts to get chilly in many areas of the U.S., we thought an ASPE Open Forum post by John Rocchio, a Senior Engineer with EP Engineering, is very timely. He is working on a project in New York City with an unheated parking garage on the second floor, with the lowest level of apartments on the third floor. The garage walls are about 50 percent open to the exterior using perforated brick. John is considering heat tracing the individual fixture drains and traps coming from fixtures in the third-floor apartments, but only insulating the sanitary mains because they would not be as susceptible to freezing as the smaller-diameter piping due to their larger diameter and more constant flow. 

As usual, our experts were eager to chime in on this topic.

Not Worth the Risk?

Generally, traps with standing water must be heat traced, but horizontal sanitary lines don’t have to be because they are either empty or have relatively warm water flowing through.

However, the question to considerer is if the cost saving of the heat maintenance cable is worth the risk of having a frozen plumbing system. Typically, additional heat tracing is fairly inexpensive insurance to help protect the owner’s investment. The larger mains may have a more consistent flow, but some of that flow (the trailing edge) may have the opportunity to develop into ice on the walls of the carrier pipe. Also, solids and toilet paper in the horizontal mains will definitely freeze. Insulation only minimizes the rate of heat transfer—it does not prevent the pipe wall temperatures from reaching a freezing condition.

If you do decide to heat trace the horizontal runs, make sure you coordinate with the electrical engineer to get power to the controllers and any interface with the building automation system. Depending on the size of the building, the additional heat tracing could necessitate increasing the size of the electrical service.

Also, make sure the heat trace is on a dedicated emergency power service that will run for at least eight hours or more during an outage.

Which Trade Is Responsible?

Rick Graham, a Plumbing Designer with Spectrum Engineers, posed a follow-up question: Who installs the heat trace? It shows up in Section 22 (Plumbing), but will a plumber know how to install it, or is it better left to the electrical contractor?

Opinions on this topic differed:

  • “Generally, I have specified the heat maintenance as part of the plumber’s work—controls and cable. It is not difficult to install if they follow the manufacturer’s installation instructions. Of course, the plumbing contractor can always subcontract that work out at their option.” —David Dexter, FNSPE, FASPE, CPD, CPI, LEED BD+C, PE
  • “In my experience, the electrician installs the freeze protection cable for all trades, not just plumbing. The plumber (or other trade) coordinates and provides insulation over it. But the scope division might depend on local conditions and union agreements between trades. Bottom line: just show it on the drawings and let the general contractor manage trade contracts.” —Gregory Shvartsman
  • “I would always specify that it be installed by the plumber, with line voltage connections made by the electricians. Plumbers will better know which pipes will need protection and pay closer attention.” —James Richardson Jr., CPD

If you want some tips on how to show heat tracing on your plans or add your two cents, follow the entire discussion on ASPE Connect.

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