South Hill sits in the same cold-moderate climate band as the rest of the area we cover, which means winters bring freeze-thaw cycles that work on any seam where moisture collects - and the bottom rail of a steel door is exactly that seam. Water gets in during a thaw, sits overnight, freezes, expands the gap a little more. Do that every winter since 1997 and the rust at the bottom of the door isn't a surprise, it's a schedule.
That's fourteen years newer than the 1983 median build year for the rest of the service area, which changes what's failing on these doors compared to older neighborhoods - South Hill isn't dealing with the one-piece doors and side-mounted hardware you find on 1960s and 70s stock elsewhere. It's dealing with sectional steel doors reaching the point where the original galvanizing is used up.
With roughly 22,789 households in South Hill built out mostly in that same window, the failure pattern repeats house to house: same door era, same panel profile, same rust line at the bottom rail. It's not random damage - it's a batch of doors all hitting the same age at once.