David Hammel, 55, of Langley Park, has been left unable to resume his work as a joiner after falling 2.5m from a wall on 9 July 2012.
Consett Magistrates' Court heard that he was an agency worker employed by Newcastle-based MGM Ltd, the principal contractor for a new-build residential care home in Front Street, Dipton, Stanley.
Hammel was part of a four-man gang installing roof trusses of various sizes to form part of the new roof. He had climbed onto and was standing on a wall plate on top of a block wall that formed the shell of a second-floor room and was waiting to receive and manoeuvre a roof truss into place. But the roof truss slipped and knocked him off the wall plate. He fell into a corridor sustaining multiple fractures of his right arm and elbow.
He since had two operations to rebuild his elbow with the insertion of a titanium hinge. He has been told by doctors he is unlikely to resume his job because he does not have full function of his arm as a result of the injuries and reconstructive surgery.
An investigation by the Health and Safety Executive (HSE) found the measures in place by MGM Ltd to prevent a fall were wholly insufficient. It identified that the firm's planned system of work required a crane to be used to lift, hold and support the trusses while they were temporally fitted into place. However, on the day of the incident there was no crane on site and the gang of joiners were allowed to install the roof trusses manually instead.
The investigation concluded that if a crane had been used it is highly unlikely that the roof truss would have fallen or slipped.
MGM Ltd of Rhodes Street, Newcastle, was fined £4,000 and ordered to pay £6,184 in costs after pleading guilty to breaching Section 3(1) of the Health and Safety at Work etc Act 1974.
HSE inspector John McGill said: "This was a wholly avoidable incident resulting in serious injury. "Work at height is inherently fraught with risk and falls remain the single biggest cause of deaths and serious injury in the construction industry. It is therefore essential that work at height is properly planned, managed and monitored to ensure it is carried out safely and that all necessary precautions are taken to prevent falls and protect workers.
"Work at height activities should only ever be undertaken by competent personnel with the right equipment, knowledge and experience.
"This incident also emphasises the need for those who control work activities to ensure that they establish safe systems of work, make sure they are adhered to and that effective supervision is in place."
Speaking after the court case Hammel said: "I hope this prosecution will act as a reminder to building contractors of the responsibilities they have to individuals on site. I'm still here to tell the tale but it could have been a lot worse. This incident has ruined my career and I wouldn't like to see it happen to anyone else."