Why do freezing pipes burst?

Burst water pipes are a big problem when temperatures drop below freezing in winter. But why do frozen pipes burst?

The simple answer is that when water freezes into ice, it expands, causing solid ice to fill more volume than the liquid that used to flow through the pipes. This ice creates pressure in the pipes, which can cause them to rupture.

“If there’s no relief, ice will just pop a pipe,” John Galeotafiore, who has a technical background and is associate director of product testing at Consumer Reports, told Live Science. His organization creates guides for home maintenance on topics such as pipe safety (opens in new tab).

“I’ve seen copper pipes that have burst,” Galeotafiore added, but says the burst can be as much a result of a weak fitting as it can be a weak spot in the pipe. Even plastic pipes are not immune, especially as the material ages.

“I’ve heard some people say, ‘Well, I have PVC or PEX plastic pipe.’ But while this could cause a slight delay in the emergence of problems, it’s really not the solution,” Galeotafiore said.

When water freezes, its molecules crystallize into an open hexagonal array that takes up more space than when the molecules are in their liquid form—meaning the water molecules expand when they freeze.

As the ice expands, it pushes liquid water towards the closed faucet. This causes immense water pressure to build up between the ice blockage and the faucet – eventually the pipe ruptures under the pressure, usually in a spot where there is little or no ice.

The pipe sections in front of this block of ice are generally not in danger of bursting because the pressure is not high enough. In this case, the water is not blocked and can flow back to its source at any time.

Pipes that are most prone to rupture are those that are exposed: outside the building’s insulation or in unheated interior areas such as basements, attics, and crawl spaces. Also at risk are mobile homes and three-season cottages with thin walls and little or no insulation; Galeotafiore said you need to flush your plumbing systems ahead of winter to reduce the risk of damage to your property.

The typical danger zone is at temperatures around 20 degrees Fahrenheit (minus 7 degrees Celsius). Danger signs to look out for include water that’s not flowing at all or water that’s flowing slower than usual, Galeotafiore said. “It’s a big sign that the pipes are starting to freeze.”

Heating or insulating these delicate tubes with fiberglass or foam sleeves can help prevent them from bursting. Additionally, keeping the faucet open and the water running—even if it’s just a trickle—helps to prevent the water pressure from building up to dangerous levels. Galeotafiore also urges people to go into their attic or crawl space on a sunny day and plug any holes in the wall that let in daylight.

However, if more insulation is required, consult a professional as there can be safety concerns or other issues associated with installing large amounts of modern insulation in a home at one time. Take extra care if your home has asbestos insulation, which can cause health problems if improperly disturbed and requires special care from licensed contractors.

If you’re going to be away from home for more than a day, Galeotafiore said, make sure your indoor temperature is above 17C to reduce the risk of pipes freezing. If possible, turn off the water at the source. While heating is expensive, he conceded, “don’t worry about the cost savings because it’s going to be a lot cheaper than fixing a broken pipe.”

If the worst happens and you have a clogged or burst pipe, here are a few steps you can take before calling a plumber. If the pipe is under a kitchen or bathroom sink in a closet, you can try opening the doors to expose the pipe to the heat of your home. Turn off the water line for a few minutes, then try running a hair dryer on the coldest part of the pipe to break up the ice. When you’re ready, slowly turn the main switch back on, Galeotafiore urged, to make sure there weren’t any leaks.

If the pipe has completely burst and flooded an area, Galeotafiore said you should never wade into standing water because you cannot be sure of your footing or protection from possible electrocution. You need a professional for that. Only turn off the water if you can do so safely without entering the flooded area; Otherwise your plumber will take care of it.

Galeotafiore added that homeowners, whether they are renting or buying, should always be aware of the age of the pipes, the type of pipes and the condition of the pipes as soon as possible before or after moving in – and stay up to date should of maintenance. Plumbing is one of the top knowledge topics, along with roofs, electrical systems, heating systems and windows, he said.

The repiped is a very expensive procedure, typically costing several thousand dollars and taking several days. Their walls will also need to be replastered and repainted after the plumbing is replaced. But this investment will go a long way towards preventing leaks and ice vulnerability in the future. If you’re lucky, insurance may cover the procedure, but check first.

Originally published on Live Science.

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