Brian Beynon, 45, from Llanelli, received serious injuries to both legs in the incident, which occurred in June 2006 in a property on Neath Road.
The company – based in Cheam, Surrey – pleaded guilty to breaching the health and safety act before Swansea Magistrates Court. It was also ordered to pay £6700 in costs.
HSE inspector Anne Marie Orrells said: "There was a systematic failure by Roalco Ltd to manage the risk on this site, which resulted in Mr Beynon falling and receiving serious injuries.
"All employers have a responsibility to ensure that safe working practices are in place, because failure to do so could well cost them dearly in terms of lost working hours, and any resulting enforcement action."