What causes pipes to burst in freezing temperatures?

When water freezes, it expands by about 9 percent in volume. As temperatures drop, 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 spaces like exterior walls, attics, basements, and crawl spaces, where insulation is minimal. Copper and steel pipes are particularly susceptible because they are rigid and cannot flex to accommodate the expanding ice. The burst often goes unnoticed until the ice thaws and water begins flowing through the crack.