Portland gets one or two real freeze events most winters — usually a cold snap where temperatures hold below 25°F for a few days. That's plenty to split an unprotected hose bib or burst the line behind it. The leak almost never shows up during the freeze itself; the ice plug seals the break. You see it when things thaw — sometimes weeks later — and water that was running into the wall framing finally finds its way to a ceiling stain or a soaked baseboard.
The single biggest cause we see is a garden hose left attached over winter. Even a frost-free hose bib relies on water draining back out of the long stem when the valve closes — a connected hose blocks that drain, so the stem fills with water and freezes. Disconnect every hose before the first freeze; that one habit prevents most of these calls.
Oregon plumbing code requires backflow prevention on every hose bib — that's the small dome on top of the spigot (a vacuum breaker) that stops contaminated water from being siphoned back into your home's supply if pressure drops. We replace with anti-siphon frost-free units that meet code, and we'll repair or replace a failed vacuum breaker on an existing spigot when that's the issue.