Mohammed Jamil had been contracted to carry out work on the garage roof at the home of husband and wife Donald and Rosetta O'Sullivan on Matlock Road, Leyton, between the 14 February and the 31 March 2009.
The Old Bailey heard that Mr Jamil was paid to raise the roof of the garage, but did not take into account the effect this would have on the safety of the gas appliances within the property.
An investigation by the Health & Safety Executive (HSE) found that in raising the roof, Mr Jamil enclosed the flue of a boiler, leaving it in a dangerous and unsafe condition. As a result, Mr O'Sullivan, 74, and Mrs O'Sullivan, 71, suffered carbon monoxide poisoning and were found dead at their home on the 21 April 2009.
Mohammed Jamil, of Grove Green Road, Leyton, pleaded guilty of breaching Regulation 8(1) of the Gas Safety (Installation & Use) Regulations 1998 for his failings in relation to the deaths. In addition to the £75,000 fine, he was ordered to pay £25,452 in costs and handed a 12 month community order requiring him to undertake 150 hours of community service.
After the hearing, HSE inspector Kevin Smith said: "This was a tragic incident that resulted in the unnecessary deaths of a retired couple in their own home as a result of carbon monoxide poisoning.
"Today's prosecution graphically illustrates the dangers of builders carrying out work without considering the effects on gas appliances. The builder failed to comply with the standards and regulations relating to gas fittings, which resulted in work that left flues in a dangerous condition, and allowed a colourless, odourless, silent killer to enter the property."