A Christchurch roofing contractor has been fined $5000 after failing to protect one of his employees from falling 5.4 metres onto concrete.

Louis James Petersen, trading as LJ Roofing, was also ordered to pay $5,000 in reparation to the injured man by the Christchurch District Court today.

Petersen had been replacing roofing iron on a commercial building in Sockburn in May 2011, and had agreed with the roofing contractor who hired him to remove and replace only one 400mm-wide sheet at a time.

Petersen later decided that removing one sheet at a time was not practical and increased it to three, leaving a 1.2m gap.

He did not amend the agreed safety procedures.

Soon after, a worker fell through the gap while carrying a replacement sheet with two others.

Department of Labour Southern manager Jean Martin said the injured man was fortunate to only suffer a fractured elbow in the fall.

"A fall of much less than this one can kill, so this worker is very fortunate, others have not been."

It was unacceptable for the employer to change the way the job was carried out without further discussion, she said.

"With no safety procedures in place, a gap of this width presented a huge danger to the workers.

"The defendant was aware of and trained in height safety measures and associated industry guidelines, but chose to do nothing to prevent a fall."

The employee had not been using a harness or safety line, and there was no fall protection, Martin said.