An access door unit includes a door, a doorway structure, and elements for pivotally attaching the door to the doorway structure. The doorway structure has an outer perimeter frame and a base affixed thereon. The base has support members extending in transverse relation to and outwardly in opposite directions from the outer perimeter frame and adapted to rest on a generally level support surface such that the outer perimeter frame extends upright from the base enabling the doorway structure to assume a free-standing, self-supporting orientation on the support surface. The outer perimeter frame of the doorway structure defines a passage large enough to fit the door and permit entry or exit through the passage when the door is opened.