David Mitchell, a director of Ferndown Developments Ltd, had hired James O’Connor, from Winton, to work at the cottage when the incident happened on 29 April 2009.
An investigation by the Health & Safety Executive (HSE) found that the property was on a sloping site and needed excavating below the level of the shallow cottage foundation in order to construct the foundations for the extension.
Mr O’Connor, 42, was in the process of lowering the ground level when the gable wall collapsed, knocking him to the ground.
At the same time, part of the wall fell through the windscreen of an excavator and hit the reverse lever. Mr O’Connor’s leg, which was on the track of the excavator, was pulled in and became trapped between the track and body of the excavator. He suffered shoulder, back and leg injuries and had to have his right leg amputated above the knee.
Dorchester Crown Court heard on Friday (5 April) that Mr Mitchell, who had been contracted to carry out the job, had not controlled the work in a safe manner. He had failed to identify the need to support the building during the excavation and foundation stages of the project.
David Mitchell, director of Ferndown Developments Ltd, Park Homer Drive, Wimborne, pleaded guilty to breaching Section 28(1) of the Construction (Design and Management) Regulations 2007 and was fined £2,000 and ordered to pay costs of £18,000.
Speaking after the prosecution, HSE inspector Frank Flannery said: "This was a very serious and wholly preventable incident in which a man in his prime lost a leg as a result of the omissions and failings during the planning and construction phases of the project.
"Had Mr Mitchell fully assessed the safety aspects of the work that he was contracted to do prior to starting, he would have identified the need to support the building during the excavation and the building of the new foundation. This would have allowed a structural engineer to be instructed prior to the work starting, and a safe system of work could have been determined."