What causes pipes to burst in freezing cold weather?

When water freezes, it expands by about 9 percent in volume. As temperatures drop below 32°F, water inside pipes begins to freeze and expand, creating enormous pressure inside the pipe. This pressure builds between the ice blockage and the closed faucet or fitting, and the pipe walls cannot withstand the force, causing them to crack or burst. Pipes most vulnerable are those in unheated or poorly insulated areas like exterior walls, attics, basements, and crawl spaces. Metal pipes, particularly copper, are common victims, though plastic pipes can burst too. The actual rupture often occurs not at the frozen section but at a weaker point nearby where pressure has concentrated.