Original header clearance
That gap matters more than it sounds. A house built in the early-to-mid 1950s often still has the original low-clearance header, sometimes framed for a door that predates any opener at all. Swapping in a modern opener box means checking headroom, checking whether the door itself is original wood or a later steel replacement, and running new wiring to a panel that was never built with a garage circuit in mind.

