A court heard how the workforce was exposed to risks of falling down unprotected holes up to nine metres deep.
John Pinn was refurbishing two Victorian terraced properties in Crwys Road, Cathays, Cardiff, in November 2012 when the failings were uncovered by a Health & Safety Executive (HSE) inspector following a complaint.
In a prosecution brought by HSE, Cardiff Magistrates heard that Mr Pinn visited the site every day and would have been aware of the dangerous conditions his builders were working in.
When the HSE inspector visited the site, he found both houses had been gutted and additional floors were being installed. There were large, unprotected holes several metres deep in the floors that posed a danger and unprotected open edges on all three upper floors of both houses, where workers could easily have fallen to the concrete basement floor below.
General site conditions were described by the inspector as 'Dickensian', with substantial accumulations of combustible waste, no fire-fighting or fire-detection equipment, electrical distribution boards with water pouring over them and no welfare facilities, such as a working toilet and basic washing equipment.
The court was told that Mr Pinn also failed to notify HSE that he had started a construction project likely to last more than 30 days. He had not appointed a principal contractor or a co-ordinator to plan, manage and monitor the work. The HSE was therefore unaware that the site existed until the complaint was made.
John Pinn, of Powisland Drive, Plymouth, pleaded guilty to two breaches of the Construction (Design and Management) Regulations 2007 and one breach of the Work at Height Regulations 2005. He was fined a total of £4,600.
Deputy District Judge Jim Davies said that it was clear Mr Pinn "was endeavouring to do the work on the cheap" and had "profited by not implementing the required health and safety procedures".
After the case, HSE inspector Liam Osborne said: "Mr Pinn knew what his responsibilities were under the law, and must have known the serious risks that his builders faced whilst working for him because he visited the site every day.
"The site conditions were Dickensian in the extreme. Planning construction work properly and managing what goes on is vital in keeping workers safe.
"Any holes should be covered and proper edge protection fitted. Falls from height are the biggest cause of workplace deaths and it's crucial that employers make sure work is properly planned and sufficient measures are put in place to protect workers from the risks."