A revised request seeking documents only from the past year that explained the delays attracted a $3759 price tag. Officials said nearly 14 hours would be needed to retrieve the documents as well as 176 hours to decide which could be released to the public.

Despite media reports on the project as far back as 2010, questions in Senate estimates hearings and millions being spent on the works – as well as a luxury Forrest home rented for the prime minister at a cost of $3000 a week – officials decided it was not in the public interest to release the documents, nor to waive costs.

A senior departmental executive, John Owens, acknowledged the documents might contribute in some way to public debate but said the release would not "advance the public interest beyond the information that is already available, as well as information that will be available, as Finance continues to publish information".

Finance was asked last week why so many documents had been created to discuss the delay. Officials provided a response that confirmed only that the documents had been created.

The refurbishment works began in September 2013. Originally expected to cost taxpayers about $3.19 million, the latest estimate is for $6.3 million. Last year's federal budget included unspecified extra funds for the work.