Freeze expansion (January–March)
The dominant cause in Brockton winters. When supply-line water drops below 20°F it crystallizes and expands roughly 9 percent by volume, generating internal pressures past 40,000 psi — far beyond what Type L copper, CPVC, or PEX-B is rated to hold. Splits occur at the weakest point, typically where the pipe passes through an unheated wall cavity, crawl space, or exterior rim joist. The first sustained sub-15°F night of January reliably produces our highest single-night burst dispatch volume.