A coworker had a similar story with his prefab. After it was delivered (and it comes delivered with sheetrock walls, electrical, and subfloor), my coworker not

A coworker had a similar story with his prefab. After it was delivered (and it comes delivered with sheetrock walls, electrical, and subfloor), my coworker noticed that the the factory forgot a step: the plumbing. The builder had to rip out lots of the sheetrock and install plumbing. Lots of mistakes occur while building a house. The difference is that when the workers are already in the field, it is generally quite inexpensive to identify and fix any problems. Not so for the prefab stuff.