"Alan and Joan should have been in control of their own lives, making decisions about how to live out their twilight years. Instead they've had an appalling nightmare to navigate over the last six years.
"It has been an incredible strain on the whole family."
He said it is a test case because many other homes are in the same position.
The problems started six months after the repair work began in February 2014.
Brick cladding needed to be replaced and a new foundation required, the $319,000 job should have been completed in around six months.
When it became apparent that the project was significantly behind schedule, Nigel got involved to help keep things moving and he found there were also issues with the quality of work.
"As we became increasingly concerned about the quality of work, we had to engage independent experts to check the work Farrells had done.
"It became clear there were major problems with the repairs, that the parties involved were either unwilling or incapable of resolving," he said.
They terminated the contract in 2015and went back to IAG.
"They basically said, sorry, the contract is between you and Farrell's, this is nothing to do with us.
"It has been a long and exhausting process, but the court has decided that the defendants were liable because the repair work did not meet the policy standard and they were in breach of the Consumer Guarantees Act."
An IAG spokesperson said the company was pleased with the result.
"We will not be challenging the decision on Mr and Mrs Sleight's insurance coverage," the spokesperson said.
"We have been doing everything we can to bring this matter to its conclusion. IAG contributed $120,000 to Mr and Mrs Sleight's legal fees for this case, as we wanted to seek a resolution for them with Hawkins and QBE (Hawkins' insurer).
"The reason this was a test case is because it was needed to establish liability for the unfinished work on Mr and Mrs Sleight's property. The Christchurch earthquakes were an unprecedented event, which led to many complex insurance claims, often involving other parties. Unfortunately, due to the uniqueness of this case and parties involved, the resolution for Mr and Mrs Sleight was not clear-cut."