Three of the six workers were buried under the debris when the roof collapsed during work to transform the third floor from a motel to hospital offices.
Two of the buried workers died, but one was found alive after a 14-hour rescue effort.
The building’s structure was too weak use heavy machinery in the rescue operation, and the number of workers assigned to the rescue had to be limited to 20 at a time to avoid a secondary collapse.
Two of the workers were found to have been crushed to death by the debris.
A third was found to have survived, having stepped outside to smoke against a wall minutes before the sudden cave-in, avoiding the direct impact of the fallen roof.
The authorities suspect that the workers had unwittingly knocked down a wall that supported the roof, mistaking it for a non-supporting partition wall to separate motel rooms.
The mistake may have arisen partly because the building differed from typical Korean structures as it was built entirely of unreinforced brickwork, and blueprints of the original construction were missing, authorities said.
The authorities plan to question whether there were any legal breaches in the reconstruction work.
The first floor of the building is being used as a Chinese restaurant and the second floor is a hospital office area.
The renovation had been intended to expand the hospital’s premises.
By Lim Jeong-yeo (firstname.lastname@example.org)