Before the First Hard Freeze: A Plumbing Walk-Through for St. Louis Commercial Buildings

Freeze season in the St. Louis area doesn't start on the same date everywhere. Under the National Weather Service's 1991–2020 normals, the median first freeze at Lambert Airport comes on November 1 and the median first hard freeze (28°F or colder) on November 15. Farther out, the cold comes sooner. The NWS St. Louis office lists a median first freeze of October 21 at the Chesterfield (Spirit of St. Louis) station and October 18 at the St. Charles County station. NWS notes that the St. Charles record has some missing years, so treat it as a rough guide. If your building is in St. Charles County or west St. Louis County, freeze season may have started already.

The seasonal outlook won't save you either. NOAA's October 15 Winter Outlook, shaped by a very strong El Niño, favors warmer-than-average temperatures for the Midwest and Mississippi Valley from December through February. But that's a statement about averages, not a promise of no cold nights. NOAA says its seasonal outlooks give probabilities for temperature and precipitation and don't forecast snowfall. The Insurance Institute for Business & Home Safety (IBHS) has warned that even as U.S. winters get shorter, arctic outbreaks still happen, especially in central states where warm and cold patterns overlap. That describes St. Louis. A mild winter with one hard cold snap can do more damage than a steady cold one, because nobody is ready for it.

This walk-through is for facility managers, property managers, and building engineers. It covers what to check before the first hard freeze.

Why pipes burst where you don't expect

Freezing pipes usually don't split at the ice. Research from the University of Illinois Building Research Council, summarized by the International Code Council, found that a solid ice blockage traps water between the ice and a closed valve or fixture. As the ice grows, pressure builds in that trapped water, and the pipe gives way downstream, often where there's little or no ice at all. The same research set a 20°F "alert threshold" for uninsulated pipes in unconditioned space and found that moving air, like wind coming through a wall opening, speeds up freezing.

For a commercial building, that changes where you look. The risk isn't just cold air. It's cold air moving across a water-filled pipe with a closed valve downstream. Facility rounds should focus on those spots.

Walk the building the way cold air does

Start at the outside walls and follow every route cold air can take into the building:

• Vestibules, stairwells, and loading docks. Dock doors stay open for long stretches, and wall hydrants and hose bibbs near docks are easy to forget. Check that every wall hydrant is frost-free and that every hose is disconnected.
• Ceiling plenums above exterior walls. Domestic water lines often run through the ceiling space along the building's edge. Look for missing insulation at roof-to-wall joints and gaps around penetrations made after the building was finished: data cable, conduit, or a rooftop unit curb.
• Mechanical, riser, and fire-service rooms on outside walls. Make sure unit heaters work and their thermostats are actually set. Check that louvers close.
• Vacant suites and partly leased floors. A dark tenant space with the heat turned down is where small problems turn into flooded ceilings.
• Irrigation and outdoor backflow assemblies. Missouri American Water's cold-weather advice tells customers to turn off and fully drain sprinkler and irrigation systems. Above-ground assemblies need insulated enclosures or a planned seasonal shutdown.

The plumbing code already expects this protection. Section 305.4 of the International Plumbing Code says water, soil, and waste pipes may not be installed outside a building, in attics or crawl spaces, concealed in outside walls, or anywhere else exposed to freezing temperatures unless they are protected by insulation, heat, or both. Exterior water piping must be at least 6 inches below the frost line and 12 inches below grade. In practice, buildings drift away from that standard. Renovations open walls, someone removes insulation to make a repair and never puts it back, and a space that was heated at turnover gets used as storage.

Fire sprinkler piping needs its own plan

A sprinkler line is one of the costliest pipes in a building to lose. The National Fire Sprinkler Association, quoting NFPA 25, says spaces with wet sprinkler piping should stay at 40°F or warmer. The wet portion of a dry-pipe valve must also stay at 40°F or above. Its enclosure must be checked daily during cold weather, or weekly if it has a low-temperature alarm. Low-point and auxiliary drains on dry systems have to be drained before freezing weather starts and as often as needed after that. Antifreeze systems need to be tested before the cold arrives.

Local buildings have learned this the hard way. In January 2026, First Alert 4 reported that a frozen sprinkler pipe broke at a private school in Chesterfield on a Sunday afternoon, when no one was there. The water reached every room, and it damaged the tenant spaces on both sides. Students had to learn remotely while repairs were made. In January 2024, KSDK reported that a broken pipe during a cold snap flooded the first three floors of the Mark Twain Building downtown, and all 213 residents had to be evacuated onto warming buses.

Sprinkler inspection, testing, and maintenance belong to your licensed fire protection contractor. The plumbing side still matters, though. The domestic service, the backflow assembly that protects it, and the heat in the rooms where those pipes enter the building all affect whether the sprinkler system freezes. Plan both together.

Know your shutoffs before you need them

When a pipe bursts, damage grows by the minute, so the most useful thing you can do before winter is make sure your team can stop the water fast. Missouri American Water's cold-weather tips say to find the main shutoff, tag it so anyone can spot it, and test it by closing it and checking that fixtures stop flowing. Ball valves usually close with a quarter turn. Gate valves close clockwise and should turn easily. If a valve sticks, have it serviced now, not during an emergency.

For a commercial building, go further:

• Label the domestic main, each riser or zone valve, and the fire-service valve. Put a simple map in the mechanical room and in your after-hours call list.
• Check that the after-hours number on that list actually reaches someone. In the same First Alert 4 report, a Lakeshire apartment resident said a frozen-pipe work order went in the night before the line burst.
• Consider low-temperature alarms for at-risk rooms. Missouri American Water suggests freeze alarms that call a chosen number if the inside temperature drops below 45°F.

Settings for holidays and shutdowns

IBHS and Missouri American Water both recommend keeping heat at no less than 55°F when a building is empty. For a commercial building, apply that to the whole building, including vacant suites and storage rooms, not just the occupied offices. If a space will sit empty through a cold stretch, you can shut it off and drain it, but do it as a planned procedure so the lines can be refilled and checked for leaks before people come back.

Letting water trickle is a short-term fix, not a plan. The International Code Council explains that an open faucet works mostly by relieving pressure between the ice and the fixture. That helps on one bad night, but it won't protect a riser in an uninsulated wall.

After a freeze: what to check before you call it done

Once a frozen line thaws, open the water slowly and look over joints and fittings. Missouri American Water says to shut off the main before thawing, warm the air around the pipe, and never use an open flame or leave a space heater unattended. Then check the equipment a freeze often damages without anyone noticing:

• Backflow assemblies. Missouri's backflow rule (10 CSR 60-11.010) requires assemblies to be tested by state-certified testers, and your water supplier sets an annual test date. If a freeze damaged an assembly, ask your supplier what they need from you before it goes back into service.
• Water heaters and expansion tanks in cold rooms, especially in buildings that lost heat.
• Underground service lines. A service line that keeps freezing usually means it isn't deep enough or the ground around it has settled. That's an excavation repair, not a heat-tape fix.

Where Legacy Plumbing fits

Legacy Plumbing's facility team handles the plumbing side of winter readiness for commercial and industrial buildings across the St. Louis metro. That includes preventive maintenance walk-throughs that flag exposed piping and bad valves, service and repair when something has already failed, and commercial water main repair when a service line between the meter and the building gives out. If you'd like a second set of eyes on your building before the first hard freeze, call our office at 636-978-0120, Monday through Friday, 7 a.m. to 4 p.m.

Frequently asked questions

When does the St. Louis area usually get its first freeze?

Under National Weather Service 1991–2020 normals, Lambert Airport's median first freeze (32°F) is November 1 and its median first hard freeze (28°F) is November 15. Outlying stations freeze earlier: the median first freeze is October 21 at Chesterfield's Spirit of St. Louis station and October 18 at the St. Charles County station, which NWS notes has some missing years of data.

What temperature should an empty commercial building be kept at to avoid frozen pipes?

IBHS and Missouri American Water both recommend keeping heat at no less than 55°F in unoccupied spaces. For fire sprinklers, the National Fire Sprinkler Association, citing NFPA 25, says areas with wet sprinkler piping should stay at 40°F or warmer, and the wet portion of a dry-pipe valve must also stay at 40°F or above.

Does NOAA's warm winter outlook mean St. Louis buildings are safe from frozen pipes?

No. NOAA's October 15, 2026 outlook favors warmer-than-average temperatures for the Midwest and Mississippi Valley, but seasonal outlooks only give probabilities. IBHS notes that arctic outbreaks still occur as winters get shorter, especially in central states, and a single cold snap is enough to freeze an exposed pipe.

What should be checked after a pipe freezes and thaws?

Shut off the main before you thaw anything, warm the air around the pipe without open flames, then open the water slowly and check joints for leaks. Check backflow assemblies, water heaters, and expansion tanks in rooms that got cold. Missouri's backflow rule requires assemblies to be tested by state-certified testers, so ask your water supplier what it needs before a damaged assembly goes back into service.

Sources

• National Weather Service St. Louis, "Frost & Freeze Decision Support Page," fall climatology, 1991–2020 normals: https://www.weather.gov/lsx/frostfreezepage
• National Weather Service St. Louis, "Latest/Earliest Freeze Dates for Saint Louis, MO (1874–present)": https://www.weather.gov/media/lsx/climate/stl/temp/temp_stl_freeze_data.pdf
• NOAA, "El Nino looms large over U.S. Winter Outlook," Oct. 15, 2026: https://www.noaa.gov/news-release/el-nino-looms-large-over-us-winter-outlook
• NOAA Climate Prediction Center, Prognostic Discussion for Long-Lead Seasonal Outlooks, Oct. 15, 2026: https://cpc.ncep.noaa.gov/products/predictions/long_range/fxus05.html
• Insurance Institute for Business & Home Safety, "IBHS Winter Weather Ready guide…," Nov. 14, 2024: https://ibhs.org/ibhs-news-releases/ibhs-winter-weather-ready-guide-provides-easy-to-do-actions-to-help-prevent-property-damage-from-colder-temperatures/
• International Code Council, "Freezing and Bursting Pipes" (summarizing University of Illinois Building Research Council findings): https://www.iccsafe.org/wp-content/uploads/DIS-FreezeBurstPipe.pdf
• International Plumbing Code Section 305.4, Freezing (via UpCodes): https://up.codes/s/protection-of-pipes-and-plumbing-system-components
• National Fire Sprinkler Association, "A Fool's Fall: Fire Sprinkler Freeze Protection," Nov. 15, 2024 (quoting NFPA 25, 2023 ed.): https://nfsa.org/2024/11/15/fire-sprinkler-freeze-protection-for-2025/
• First Alert 4 (KMOV), "Thawing pipes leaves a mess to clean up at home and school," Jan. 28, 2026: https://www.firstalert4.com/2026/01/29/thawing-pipes-leaves-mess-clean-up-home-school/
• KSDK, "200-plus residents displaced by flooding from broken pipe at downtown St. Louis apartment building," Jan. 16, 2024: https://www.ksdk.com/article/news/local/broken-pipe-floods-downtown-apartment-hundreds-evacuated/63-771d484d-b060-4113-947e-91353c8c1f9a
• Missouri American Water, "Missouri American Water Urges Customers to Prepare for Cold Weather," Dec. 4, 2025: https://newsroom.amwater.com/2025-12-04-Missouri-American-Water-Urges-Customers-to-Prepare-for-Cold-Weather
• Missouri Code of State Regulations, 10 CSR 60-11.010, Prevention of Backflow (via Cornell LII): https://www.law.cornell.edu/regulations/missouri/10-CSR-60-11-010