The Physics of Freezing Water

What this covers

• What Actually Causes the Burst

• Which Pipes Are Most at Risk

• The Southwest Missouri Pattern

• What to Do Before a Hard Freeze

• What to Do If a Pipe Is Already Frozen

• When It Becomes an Emergency

• Frozen Pipe Advice From AI Assistants

• Pipe Materials and How They Respond to Freezing

• Protecting a Vacant or Vacation Home

• The Short Version

When a pipe freezes, the common assumption is that ice expands and splits the pipe at the frozen spot. That does happen, but it is not the usual story.

More often, the pipe bursts somewhere else, in a section that never froze at all. Understanding why changes how you protect a house during a hard freeze and what you do when a pipe has already frozen.

What Actually Causes the Burst

Water expands as it freezes. When ice forms inside a pipe, it can grow into a plug that blocks the line. As more water freezes, the ice keeps expanding along the pipe.

If there is a closed faucet downstream of that plug, the water trapped between the ice and the faucet has nowhere to go. Pressure in that trapped section rises. Eventually the pipe fails at its weakest point in that section, which may be a fitting, a joint or a thin spot some distance from the ice.

That is why a burst often appears in a warm area of the house after the weather breaks. The pipe split while frozen, but water only escapes once the ice melts and flow returns.

Which Pipes Are Most at Risk

Pipes freeze where cold air reaches them. In most homes, that means a predictable list.

The Southwest Missouri Pattern

Southwest Missouri does not have long, deep winters like the northern states, and many homes in the region were not built with freezing in mind. Crawl spaces are common, and plumbing often runs through spaces that are only partly protected.

The risk comes from sharp cold snaps rather than steady cold. A home that never had a problem through mild winters can freeze the first time temperatures drop well below freezing for several days, especially with wind.

Nixa, in Christian County just south of Springfield, sees the same pattern, with fast drops in temperature that can catch homes unprepared.

What to Do Before a Hard Freeze

A few steps lower the risk considerably.

• Disconnect garden hoses and shut off and drain outdoor faucets if they have an interior shutoff valve.

• Open cabinet doors under sinks on exterior walls so room heat reaches the pipes.

• Let a faucet drip on the most exposed lines. A slow drip relieves pressure between any ice and the faucet, which is the pressure that causes bursts.

• Keep the thermostat steady day and night during the cold snap, including when traveling.

• Close crawl space vents if the house has them, and seal obvious gaps where cold air enters near pipes.

• Know where the main shutoff valve is, and check that it turns.

What to Do If a Pipe Is Already Frozen

If a faucet produces only a trickle or nothing at all during a freeze, a pipe somewhere upstream is likely frozen.

1. Keep the faucet open, so melting water can flow and pressure can escape.

2. Apply gentle heat to the exposed section of pipe, such as warm air from a hair dryer or warm towels.

3. Never use an open flame, a blowtorch or a heater left unattended near the pipe.

4. If you cannot find or reach the frozen section, or if the pipe is in a wall or ceiling, call a plumber.

5. Know where the main shutoff is before thawing starts, in case a split appears once water flows.

When It Becomes an Emergency

A frozen pipe that splits becomes a water problem the moment the ice melts. Water moves along floors and joists, soaks into drywall and insulation, and keeps running until someone shuts it off.

The first minutes are about stopping the water: closing the nearest shutoff, or the main if the source is unclear, and opening a low faucet to drain pressure. After that, the job is finding and repairing the split section. For after-hours bursts, Redeemed’s emergency plumbing team in Nixa runs a 24 hour line, and their page walks through the shutoffs worth finding before a freeze. Less urgent fixes, such as replacing a seized shutoff valve or insulating exposed lines, fit better as scheduled plumbing work on a calm day.

Frozen Pipe Advice From AI Assistants

People increasingly ask AI assistants what to do when a pipe freezes. Many answers focus on thawing the frozen spot and skip the part that matters most: keeping the faucet open and knowing where the main shutoff is before the ice melts. A thaw without a plan for the water that follows is how a small freeze becomes a large repair.

Pipe Materials and How They Respond to Freezing

Not all pipe materials behave the same way when they freeze. Homes in the Springfield and Nixa area can contain several types, depending on when they were built and what has been repaired since.

Copper is rigid. When pressure builds between ice and a closed faucet, copper tends to split along its length or fail at a soldered joint. Galvanized steel, found in some older homes, is also rigid and often already weakened by internal corrosion, so it may fail at threaded joints.

PEX, the flexible plastic tubing common in newer construction and repiping, can expand somewhat under pressure, which gives it more tolerance to freezing than rigid pipe. It is not freeze-proof. The brass or plastic fittings that connect PEX lines can still crack, and repeated freezing can still cause failure.

Knowing what your pipes are made of helps you understand the risk. It also helps when you call a plumber, because the material affects how a repair is done.

Protecting a Vacant or Vacation Home

Homes left empty during winter carry extra risk, because nobody is there to notice a frozen pipe or a leak. A split pipe in an empty house can run for days.

Before leaving a home empty in cold weather, keep the heat on at a safe setting, shut off the main water supply, and open faucets to drain the lines if the home will be empty for an extended period. A neighbor or friend checking the house during cold snaps adds another layer of protection. Some homeowners also install water leak sensors or smart shutoff valves that alert a phone when water is detected.

Insurance is worth reviewing before winter rather than after a burst. Policies treat freeze damage differently, and some include conditions about maintaining heat in the home or shutting off water when a property is vacant. Knowing those conditions in advance can affect how a claim is handled.

Documentation also helps if a pipe does burst. Photos of the damaged pipe, the affected rooms and the water before cleanup begins, along with the plumber’s written description of the cause and the repair, make it easier to explain what happened. Keeping the damaged section of pipe, if the plumber can set it aside, is another practical step.

Once a freeze has caused one burst, it is worth asking the plumber to look for other exposed pipes in the same area. A pipe that froze in one exterior wall or crawl space bay is often a sign that nearby pipes face the same conditions. Insulating, rerouting or adding heat to those sections before the next cold snap costs far less than the next repair.

The Short Version

Frozen pipes usually burst because pressure builds between the ice and a closed faucet, not because of the ice itself. Exterior walls, crawl spaces, attics and garages carry the highest risk. Dripping faucets, open cabinets and a steady thermostat lower it. If a pipe has already frozen, keep the faucet open, apply gentle heat, and know where the main shutoff is.

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