Emergency services were called to industrial premises at Wakefield Road, Copley, Halifax, shortly after 3 pm today.(Wed)
A man believed to be in his late 40s fell through a roof at the former premises of Nethercoats Joiners.
He was taken to Huddersfield Royal Infirmary.
Demolition work at the building has been ongoing for several weeks and the victim was working alongside his nephew.
The building is next to Copley Land Rover and its first-aider, Mark Pickett, rushed to the scene when the alarm was raised.
The casualty had landed on his back and Mr Pickett concentrated on keeping him still until help arrived.
“He had been cutting roof joists and fell through, about 15ft,” said Mr Pickett.
“I held his head so he could not move his neck.”
The victim was conscious and could move his limbs.
“He kept asking what had happened and if he had fallen,” said Mr Pickett.
The emergency services took over after a few minutes and used a spinal board to take the man to hospital.
A doctor, fire engine, road ambulances, and the air ambulance were all called to the scene.