Winter Pipe Freeze Leaks: What to Check After a Cold Snap

Why freezing pipes split

Water expands as it freezes. When a section of pipe is full of ice, the pressure builds in the space between the ice and the closed faucet, and the pipe can crack at its weakest point. The crack may be too small to notice while the water is still frozen. Once the pipe thaws, water escapes through the split and can run for hours before anyone sees it. That is why the leak often appears after a cold night, not during it.

Pipes are most exposed where the house is least heated. Common spots include supply lines in exterior walls, pipes in crawl spaces, water lines running through an unheated garage, and lines under a kitchen or bathroom vanity on an outside wall. Hose bibs and irrigation lines outdoors are another common failure point, especially if a hose was left connected through the fall.

Signs to look for after a cold snap

Check the usual trouble spots once the weather warms enough for the pipes to thaw. Look for:

• Water staining on a ceiling or wall below a bathroom, kitchen or an exterior wall
• A soft, bulging or discolored section of drywall, flooring or subfloor
• A musty smell in a basement, crawl space or closet that was not there before
• Reduced water pressure at one or more faucets, which can point to a blockage or a partial split
• Frost or condensation on a pipe that is still cold, which can show where water is escaping
• A water meter that keeps moving when every fixture is turned off

If you find any of these, shut off the water at the main valve before doing anything else. Knowing where that valve is, before there is an emergency, saves a great deal of damage. Ask the household to stop using water until the leak has been located.

Prevention that works before the next freeze

Most freeze damage can be prevented with simple steps taken before the temperature drops. Keep the thermostat at a steady setting day and night, because a house that is cooled to a low setting while away is the most common cause of a burst line. On nights when the forecast is well below freezing, open the cabinet doors under sinks on exterior walls so warm room air can reach the pipes. Letting a faucet drip slowly on the coldest nights also keeps water moving, which makes freezing less likely.

Disconnect garden hoses from outdoor hose bibs and drain them. Some outdoor shutoff valves have a drain cap, and a few can be opened to drain the line behind them, depending on the type installed. Insulate exposed pipes in crawl spaces, garages and basements with foam sleeves or wrap, and seal drafts around pipe penetrations in exterior walls. These steps cost little and protect pipes that are hard to reach once they freeze.

What not to do when a pipe is frozen

Do not thaw a frozen pipe with an open flame, a torch or a heat gun held in one spot. These can ignite nearby materials and can also damage the pipe. Gentle, even heat is safer. A hair dryer or a space heater placed at a safe distance, with the faucet open, usually works better. If the pipe is in a wall or ceiling and you cannot reach it, do not cut into the wall yourself until a provider has confirmed the location of the problem.

Also avoid running water through a pipe you suspect is split. Pushing water through a crack can spread the damage, and it can wet insulation or flooring that might otherwise dry out.

When to call for help

Call a provider as soon as you find a leak, a suspected split or a pipe that will not thaw. A leak inside a wall or under a floor is difficult to find by looking, and the fix often depends on exactly where the break is. A provider can often narrow down the location before anything is opened. Calling (708) 221-8167 connects you with a local provider who serves your area. Describe where the cold pipe is, whether the water is still shut off, and whether you can see any staining.

For the leak types most often involved in a freeze, see our hidden pipe leak detection page for leaks inside walls and floors, and our water line leak detection page for supply lines that run under the yard or the slab. If the leak is near a basement wall or floor, the basement leak detection page explains how providers separate a pipe leak from seepage.

After the thaw

Once the weather has stayed above freezing for a few days, check the pipes you were worried about before you return to normal use. Run each faucet slowly and watch for sputtering, reduced flow or a sudden drop in pressure, since any of these can mean a pipe is still partly blocked or cracked. Keep a towel or a shallow pan under exposed valves and joints for a day, so a slow leak shows itself before it reaches the floor. If the house was empty during the cold, check the water heater and the shutoff valves too, because they are easy to overlook.

A short checklist

1. Shut off the main water valve if you find water where it should not be.
2. Note the location and the time you first noticed it, with photographs if it is safe.
3. Check the thermostat setting and any pipes in exterior walls or crawl spaces.
4. Call (708) 221-8167 and describe what you have seen.