The owner of a Worcester Park loft conversion business has promised action after the company was fined £6,000 over safety failings.
Stacy Owens, of More Than Lofts, said he has spent more than £70,000 on health and safety improvements since the accident last June, when a 17-year-old labourer fell 4m from a hole in a loft.
The teen escaped with cuts and bruises.
Mr Owens said despite "strict guidance" given to foremen, "You can't be over them 24 hours a day."
He added: "We try and do good work, and it's very difficult.
"The materials were there on site so it wasn't like we were trying to cut costs - we're not cutthroat.
"We've got to review all of our health and safety. We've made massive changes since last year."
The family firm, which employs about 40 full-time staff, was fined by magistrates at Westminster Magistrates' Court this week after being prosecuted by the Health and Safety Executive (HSE).
HSE inspector Gavin Pugh said: "This young man had an extremely lucky escape from what could have been a fatal or severe injury in a fall of that distance.
"He and his co-workers were put in unnecessary danger by the careless approach to safety demonstrated by More Than Lofts.
"The company had ample materials on site to cover over fragile surfaces during work on this loft conversion but failed to do so."
More Than Lofts admitted breaching work at height regulations and was also ordered to pay costs of £729.
Mr Owens said the employee, from Morden, was still working for his company.