The 67-year-old injured man from Sunderland, who has asked not to be named, was working for David Brian Riseborough, trading as The North Eastern Demolition Company, when the incident happened on 29 June 2010.
Mr Riseborough's firm was demolishing a pub in the city's Cox Green Road and had chosen to remove the slates and timbers of the pitched roof by hand. A mobile access platform was used to provide access for the workers and act as a barrier to prevent falls from the roof edge.
However, as the platform did not cover the whole length of the roof, Mr Riseborough should have implemented additional controls to provide a safe system of work but many of these controls were lacking, or where provided, not effective.
While working on the roof the worker fell two-storeys - around 20ft - to the ground below. He suffered serious injuries including several fractures to three vertebrae, his right elbow and both bones of his lower right leg. He also suffered a dislocated right hip and his right lung collapsed.
As a result of the terrible injuries to his spine, all his limbs are now paralysed and he requires permanent care in a nursing home.
Sunderland Magistrates' Court heard that it was unnecessary for any work at height to be carried out at all, as the demolition could have been done using a 360 degree mechanical excavator that was on site.
HSE's investigation also found the way in which the work was carried out was unsafe as the instruction and supervision of the employees was not suitable and sufficient.
David Brian Riseborough, 67, of Willow Green, Ashbrooke, Sunderland was fined a total of £20,000 (£10,000 on each charge) and ordered to pay £7,434 in costs after pleading guilty to breaching Section 2(1) of the Health and Safety at Work etc Act 1974 and Regulation 6(2) of the Work at Height Regulations 2005.
Speaking after the case, HSE inspector Keith Partington said: "The building could have been safely demolished by remote mechanical means using the excavator that was on the site - without the risks to the public, which the defendant claimed was the reason for manually dismantling the roof.
"In choosing to undertake the work at height the system the defendant used was not sufficiently robust enough to prevent one of his employees falling from the roof level to the ground which resulted in injuries that have left this worker in a condition whereby he now needs permanent care to assist him in his daily living.
"Falls from height are one of the largest causes of death and serious injury in the construction industry the consequences of which affect not only the victims, but their families and the community and thus work at height should be planned for carefully, with suitable and sufficient instruction and supervision when executed."