Market Drayton Magistrate's heard the 42-year-old subcontractor had been barrowing bricks and rubble along planks at first floor height at the Wem Mill in Shropshire last November when he fell onto the concrete floor below.
The Health and Safety Executive said not only were no suitable measures taken to prevent such an accident, but the firm had contravened other regulations by not notifying HSE of the accident within the required timescale.
HSE inspector Martin Overstall said: "It was clearly evident that workers were at risk of falling from a height which was very likely to cause substantial injuries or death. The exact circumstances of the accident were unclear because it was reported late to HSE. However, the simple fact remains that someone fell due to lack of sufficient safety measures and was seriously injured.
"Incidents like these could be avoided if companies ensured that they had assessed the risks of working at height."
The company, which pleaded guilty to a breach of the Work at Height Regulations and the Reporting of Injuries, Diseases and Dangerous Occurrences Regulation, was also ordered to pay £1,880 in costs.