Frozen and Burst Pipes: Why They Burst and What to Do

Why do pipes burst when it freezes?

Water expands when it turns to ice, and that expansion puts tremendous pressure on whatever holds it. A pipe can break no matter how strong it is (Red Cross).

It usually takes more than a light frost. Field tests by the Building Research Council at the University of Illinois found that uninsulated pipes in an unheated attic started to freeze when the outdoor temperature fell to 20°F or below. Water also supercools a few degrees below freezing before ice forms (ICC summary of the research).

Wind changes the math. Pipes near cracks in an outside wall, or in spots with little insulation, can freeze above 20°F, especially on a windy night (same source).

Which pipes are most likely to freeze?

• Outdoor hose bibs, sprinkler lines, and pool supply lines
• Supply pipes in unheated spaces: basements, crawl spaces, attics, and garages
• Pipes inside kitchen and bathroom cabinets on outside walls
• Any pipe running along an exterior wall with little or no insulation

List from the American Red Cross.

How can you tell a pipe has frozen?

• You turn on a faucet and get only a trickle, or nothing.
• One fixture has no water while the others work.
• Frost on an exposed pipe, or a section that looks bulged.
• Odd smells from a drain, or gurgling when you run water.

A frozen pipe is not always a burst pipe yet. But a crack often shows up only when the ice melts and water starts flowing again, so keep an eye on it as it thaws.

What should you do the moment a pipe bursts?

1. Shut off the main water valve. It is usually where the water line enters the house, near the water heater, or in a crawl space or basement. Learn where yours is before you need it.
2. Turn off the water heater. Switch off the breaker for an electric unit, or set a gas unit to pilot, so it does not run empty.
3. Cut power to wet rooms, but only if you can reach the panel from a dry spot.
4. Open a faucet at the lowest point in the house to drain the water still in the lines.
5. Photograph everything before you move anything: the break, the water, and damaged belongings.
6. Call for water removal and a plumber. The plumber repairs the pipe. A water damage restoration company extracts the water and dries the walls, floors, and cabinets.
7. Report the claim to your insurance company and write down the claim number.

How do you thaw a frozen pipe safely?

If a pipe is frozen but not broken, the Red Cross recommends this approach:

• Leave the faucet open. Running water helps melt the ice.
• Warm the frozen section with an electric heating pad, a hair dryer, a space heater kept away from anything flammable, or towels soaked in hot water.
• Keep applying heat until full water pressure comes back.
• Check the other faucets. If one pipe froze, others may have too.

Never use a blowtorch, kerosene or propane heater, charcoal stove, or any open flame to thaw a pipe. Call a licensed plumber if you cannot find the frozen spot or cannot reach it.

How do you keep pipes from freezing again?

• Open cabinet doors under sinks on outside walls during a freeze.
• Let a cold-water faucet drip on very cold nights. Even a trickle helps.
• Keep the thermostat at the same temperature day and night.
• If you leave home in cold weather, keep the heat set no lower than 55°F.
• Disconnect hoses, close the inside valve to outdoor spigots, and drain them.
• Insulate pipes in attics, crawl spaces, and garages.

Prevention steps from the American Red Cross.

Is a burst pipe covered by insurance?

Often, yes. Homeowners policies usually cover burst pipes, including frozen pipes, as long as you keep your home properly heated (Washington Office of the Insurance Commissioner).

The policy generally pays for the damage the water caused, not for fixing the pipe itself (NerdWallet). A vacant or unheated house is a common reason frozen-pipe claims get questioned. Your policy wording decides, so ask your agent. See what homeowners insurance covers.

Common questions

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