A Swindon-based firm has been fined £5,000 for breaching safety regulations after an apprentice electrician fell through a ceiling and broke his back.
Richard O'Connor, 18, was injured in February 2010 while working at a youth centre on Farringdon Road.
Roberts and Prowse (Swindon) Ltd pleaded guilty at Swindon Magistrates in a prosecution brought by the Health and Safety Executive.
The company was also ordered to pay £5,156 in legal costs.
The court heard Mr O'Connor was carrying out electrical installation work when he stumbled from a narrow timber walkway and fell onto an exposed plasterboard ceiling that gave way under his weight.
He managed to grab hold of a timber joist, but after a few seconds that also gave way and he fell 5.5m (18 ft) onto the floor below.
Mr O'Connor suffered three fractures to his vertebrae as well as cuts and bruising. His injuries meant he was unable to work for two months.
The court heard the company had failed to carry out a specific risk assessment for the work, and failed to ensure adequate measures were put in place to reduce the risk of a fall.
The firm, which is officially registered at Barnfield Crescent, Exeter, pleaded guilty to a breach of Section 2(1) of the Health and Safety at Work Act 1974.