When water freezes, it expands. That’s why a can of soda explodes if it’s put into a freezer to chill quickly and forgotten. When water freezes in a pipe, it expands the same way, and if it expands enough, the pipe bursts, water escapes and serious damage results.
Why Pipes Burst
Surprisingly, ice forming in a pipe does not typically cause a break where the ice blockage occurs. It’s not the radial expansion of ice against the wall of the pipe that causes the break. Rather, following a complete ice blockage in a pipe, continued freezing and expansion inside the pipe causes water pressure to increase downstream – between the ice blockage and a closed faucet at the end. It’s this increase in water pressure that leads to pipe failure. Usually the pipe bursts where little or no ice has formed. Upstream from the ice blockage the water can always retreat back towards its source, so there is no pressure build-up to cause a break. Water has to freeze for ice blockages to occur. Pipes that are adequately protected along their entire length by placement within the building’s insulation, insulation on the pipe itself, or heating, are safe.
Generally, houses in colder climates are built with the water pipes located on the inside of the building insulation, which protects the pipes from subfreezing weather. However, in the Lower Mainland (Vancouver and its area) a much milder weather is typical, thus pipes are often more vulnerable to winter cold spells. The pipes are more likely to be located in unprotected areas outside of the building insulation, and homeowners tend to be less aware of freezing problems, which may occur only once or twice a season.
Pipes in attics, crawl spaces and outside walls are all vulnerable to freezing, especially if there are cracks or openings that allow cold, outside air to flow across the pipes – wind chill can play a significant role in freezing and subsequent bursting in water pipes.
Holes in an outside wall where television, cable or telephone lines enter can provide access for cold air to reach pipes. The size of pipes and their composition (e.g., copper or PVC) have some bearing on how fast ice forms, but they are relatively minor factors in pipe bursting compared with the absence of heat, pipe insulation and exposure to a flow of subfreezing air.
When Is It Cold Enough To Freeze?
When should you, the homeowner be alert to the danger of freezing pipes? That depends, but in Greater Vancouver where freezing weather is the exception rather than the rule (and where houses often do not provide adequate built-in protection), it would be safe to say to take precautions in subzero temperature (under 32°F or 0 °C) though a research conducted at the University of Illinois puts the temperature alert threshold at 20°F/-6°C.
However, it also says that freezing incidents can occur when the temperature remains above 20° F/-6°C. Pipes exposed to cold air (especially flowing air, as on a windy day) because of cracks in an outside wall or due to lack of insulation are vulnerable to freezing at temperatures above this threshold.
What Can You Do?
There are simple things that can be done beside a major pipe insulation project.
– Cracks and holes in outside walls and foundations near water pipes can be sealed with caulking to keep cold wind away from them.
– Letting a faucet drip during extreme cold weather can prevent a pipe from bursting – even a very slow drip. It’s not that a small flow of water prevents freezing, (it helps) but rather it will provide relief from the excessive pressure that builds up between the faucet and the ice blockage. It does wastes some water though.
– Shutting off and draining of water any pipe that runs through an unheated or unprotected space (winterization). It’s not necessary to leave the affected water fixtures open in this case, since the pipe will be filled mostly with air.
– You can also insulate the spigot by wrapping around some plastic.
– When away from the house (on a trip) for extended period during the cold season, be careful how much you lower the heat. You may save a few bucks on the heating bill but there could be a disaster if a cold spell strikes and pipes that normally would be safe, freeze and burst.