A Cork Coroner's Court inquest heard that Sean had been told by the two workmen he shouldn't be in the attic and that he should go back downstairs.
Just minutes later his mother heard a loud bang from the hallway and was horrified to realise it was her son who had just fallen through the attic stairs hatch.
"All I can remember is that I heard a really loud bang from the corridor," she said.
"I could see the attic door was open and the (stairs) was open halfway. Sean was lying on the ground. He tried to let out a few yelps and screams but he could not."
The accident happened shortly after 3pm on June 1, 2011.
Two workmen, Aidan Fitzgerald and Tony Daly, were working on an attic conversion which they accessed via a work ladder.
For safety reasons, the men had placed a piece of mortarboard and a plank over the hatch of an attic folding stairs which was not being used.
Both men said they regarded the hatch as a hazard because it was not designed to take any weight from above.
The folding attic stairs was of an older design with a latch that could not prevent its opening if any weight was placed on it from above.
Sean was rushed to Kerry General Hospital in Tralee before being transferred two hours later to Cork University Hospital.
Sean died 17 days later on June 18 without having regained consciousness.
The Health & Safety Authority conducted a probe into the matter but no further action was directed.
A verdict of accidental death was returned.