The median home in South San Francisco went up around 1963, which puts most of this town's garage openings right in the middle of the first wave of sectional doors replacing the old single-panel swing-up style. Builders in that era used lightweight steel or wood-composite panels on torsion springs sized for a door that weighed a fraction of what a modern insulated door weighs. That mismatch is the root of most of the service calls we get from this part of the service area: a homeowner swaps in a heavier, better-insulated door and the original spring and opener, still doing the job sixty years on, can't keep up.
With 21,870 households in South San Francisco, a sizable share of them are sitting on a door and hardware combination that predates any opener with a modern safety reversal sensor. That's not a scare line - it's just what the build date tells you. When we install new, we're not matching a door to a house built last year. We're matching it to a frame and header that were sized for 1963 expectations, and that changes what track, spring, and opener we spec.
We travel the 9 miles from Alameda for these jobs, so we're not guessing at what's common here - we're accounting for it before the first panel goes up.