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Why Do Pipes Freeze and Burst in Cold Weather?

Last updated October 26, 2026

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The short answer

What Happens Inside a Frozen Pipe

When outdoor temperatures stay below freezing for several hours, the water in exposed pipes can lose enough heat to form ice crystals. This usually starts in unheated areas like crawlspaces, attics, garages, or exterior walls with little insulation. As ice forms, it expands by about nine percent, but the pipe's rigid walls don't stretch much.

The real problem is pressure. If ice blocks the pipe completely, the water trapped between the plug and a closed faucet has nowhere to go. That trapped water builds pressure as it freezes, and that pressure can exceed the pipe's strength. A crack may form immediately, or it may appear later when the ice melts and water flows again.

  • Ice expands and pushes against the pipe walls
  • Trapped water between ice and a closed faucet builds pressure
  • Cracks can form during the freeze or after thawing
  • Even small cracks can leak a surprising amount of water
  • Unheated spaces are the most common places for freezing

Which Pipes Are Most at Risk

Pipes in unheated zones are the most vulnerable. That includes pipes running through attics, basements, crawlspaces, garages, and exterior walls with little or no insulation. Pipes on the outside of a building, such as hose bibs or sprinkler lines, are also at high risk because they have direct exposure to cold air.

Pipes with a smaller diameter, like half-inch lines, can freeze faster than larger ones because they hold less water and have more surface area relative to their volume. Pipes near drafty spots, such as gaps around vents, windows, or where wires enter the home, are also more likely to freeze. Even in a mild climate, a sudden cold snap can catch you off guard.

  • Attics, crawlspaces, and garages
  • Exterior walls with little insulation
  • Hose bibs and sprinkler lines
  • Small-diameter pipes
  • Pipes near drafts or gaps in the building

How to Prevent Pipes from Freezing

The right way to prevent a burst is to keep pipes from freezing in the first place. Insulate exposed pipes with foam sleeves or heat tape, especially in unheated areas. Seal gaps and cracks around pipes where cold air can reach them. During a cold snap, let a trickle of water run from faucets served by exposed pipes; moving water is less likely to freeze. Policies vary, and your insurer decides what is covered if damage occurs.

Keep garage doors closed if water lines run through the garage. Open cabinet doors under sinks to let warm air circulate around the pipes. If you plan to be away, set your thermostat no lower than 55F and consider shutting off the main water valve and draining the system. These simple steps can make a big difference.

  • Insulate pipes in unheated spaces
  • Seal gaps around pipes and vents
  • Let a trickle of water run during freezing weather
  • Keep garage doors closed if lines run through
  • Open cabinet doors to let warm air reach pipes
  • Know your shutoff valve location

What to Do If a Pipe Bursts

If a pipe bursts, act quickly to limit water damage. First, shut off the main water valve to stop the flow. Then turn off the electricity to any affected rooms if water is near outlets or appliances. Open faucets to drain remaining water from the system, and take photos of the damage for your insurance records.

Next, remove as much standing water as you can with mops, towels, or a wet vacuum. The sooner you dry things out, the less chance mold has to grow. Move furniture and belongings to a dry area if possible. If the water has soaked into drywall, flooring, or insulation, those materials may need to be removed.

  • Shut off the main water valve immediately
  • Turn off electricity in affected areas if safe
  • Open faucets to drain the system
  • Remove standing water with mops or a wet vacuum
  • Move belongings to a dry spot
  • Call local water damage pros for serious damage

When to Call a Pro for Burst Pipe Cleanup

You don't need to call a pro for a small leak that you can dry quickly. But if water has soaked into drywall, carpet, insulation, or wood flooring, the damage can be hidden and persistent. Moisture trapped behind walls can lead to mold and structural issues, even if the surface looks dry.

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Frequently asked questions

How long does it take for pipes to freeze?

There's no set time, but pipes can freeze when temperatures stay below 32F for several hours. Unheated spaces and poor insulation speed up the process. In a mild climate like Bellingham, a hard freeze overnight can be enough, so keep an eye on the forecast.

Can a pipe burst without freezing?

Yes, pipes can burst from other causes like corrosion, high water pressure, or physical damage. But freezing is a common cause in cold weather. If you have a leak and it's cold outside, frozen pipes are a likely suspect, but a plumber can help determine the exact cause.

What should I do if I find a frozen pipe?

Turn off the main water valve first to prevent a burst. Then gently warm the pipe with a hair dryer or space heater, starting from the faucet end. Never use an open flame. If the pipe has already burst, shut off the water and call local water damage pros for cleanup.

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