A frozen pipe is one of the few plumbing problems that can go from a minor inconvenience to thousands of dollars in water damage in a single night. When water freezes inside a pipe, it expands and builds pressure between the ice blockage and a closed faucet. That pressure — not the ice itself — is what usually splits the pipe, and the real flooding often starts when the ice thaws and water rushes through the crack.
The good news is that frozen pipes are largely preventable with a little preparation each fall. This guide explains which pipes are most vulnerable, how to protect them before cold weather arrives, and how to respond safely if a pipe freezes.
Water expands by about nine percent when it freezes. Inside a rigid copper, PVC, or PEX pipe, that expansion has nowhere to go, so pressure builds rapidly. PEX tubing can flex slightly and is somewhat more freeze-tolerant, but no residential pipe is truly freeze-proof. Once pressure exceeds what the pipe or a fitting can handle, the pipe splits — often lengthwise along several inches.
Many homeowners are surprised to learn that the burst usually happens in a section of pipe that never froze at all. The ice forms a plug, and water trapped between the plug and a closed valve or faucet gets compressed until something gives. That is why plumbers always tell you to open the faucet slightly when dealing with a freeze: it gives the pressure somewhere to go.
Pipes in unheated or poorly insulated spaces freeze first. The usual suspects include supply lines running through attics, crawl spaces, garages, and exterior walls — especially walls facing north or exposed to wind. Outdoor hose bibs and the short pipe sections feeding them are classic freeze points. Pipes under kitchen or bathroom sinks on exterior walls are also vulnerable because cold air seeps in around the cabinet.
Homes in milder climates are actually at higher risk in some ways, because their pipes may have little or no insulation and run through unconditioned attics. A single unusually cold night can freeze pipes that have never been a problem before. If your home has a history of freezing, or if neighbors have had burst pipes, assume yours are vulnerable too.
Start with insulation. Foam pipe sleeves are inexpensive, slip on in minutes, and make a real difference on exposed runs in attics, crawl spaces, basements, and garages. For especially vulnerable sections, electric heat tape or heat cable with a built-in thermostat provides active protection — just follow the manufacturer's instructions carefully and never overlap the cable over itself.
Next, seal the cold air out. Use caulk or expanding foam to close gaps where pipes pass through exterior walls, rim joists, and foundations. Open cabinet doors under sinks on exterior walls during cold snaps so warm room air can reach the pipes. Keep the garage door closed if water lines run through the garage, and never set the thermostat below 55 degrees, even when you are away. For a full seasonal rundown, see our fall plumbing maintenance checklist.
During extreme cold, let faucets served by vulnerable pipes drip slightly — both hot and cold sides. Moving water is much harder to freeze, and the open faucet relieves pressure if ice does start to form. It costs pennies in water and can prevent a five-figure insurance claim.
The first sign is usually a faucet that produces only a trickle or nothing at all during freezing weather. If that happens, keep the faucet open and check the rest of the house: if only one fixture is affected, the freeze is in the branch line serving it; if several fixtures on the same run are out, the blockage is in a shared section. Look for frost on exposed pipes, bulging sections, or strange odors from the faucet, which can occur when only part of the pipe is blocked.
Before you start thawing, locate your main water shutoff valve and make sure you can operate it. If the pipe has already cracked, water will start flowing as soon as the ice melts, and you will need to shut the water off fast. Place buckets and towels near the suspected freeze area and any visible fittings downstream of it.
Work from the faucet back toward the frozen section so melting water and steam have an escape path. A hair dryer on a medium setting, moved slowly back and forth, is the safest tool for most homeowners. You can also wrap the pipe in towels soaked in hot water, replacing them as they cool, or use a portable space heater aimed at the area from a safe distance.
Never use an open flame — no blowtorches, propane heaters, or charcoal. Open flames can ignite wood framing, melt solder joints and plastic pipe, and even boil the water inside the pipe into steam, which can cause a violent rupture. Be patient: thawing can take thirty minutes or more, and rushing it with excessive heat risks exactly the burst you are trying to avoid. Once water flows normally, keep the faucet running briefly and inspect the full length of the pipe for drips or spraying at joints.
Call a professional if you cannot locate the frozen section, if the pipe is hidden inside a wall or ceiling, if water flow does not return after reasonable thawing attempts, or if you find any sign of a crack or leak. A plumber can use thermal imaging to pinpoint the freeze, open the wall cleanly if access is needed, and repair or replace damaged sections. If a pipe has burst and you cannot stop the water, shut off the main valve and call for emergency help immediately.
Frozen pipes and hidden leaks often go together — ice can shift fittings just enough to create slow seeps that appear weeks later. After any freeze event, it is worth reviewing how to spot hidden water leaks so small problems do not turn into mold or structural damage.
Connect with local plumbing professionals who can winterize your pipes, thaw frozen lines, and repair bursts fast.
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