The work estimate for the project to fix the heritage structure appears on a single line of the federal public accounts for the fiscal year 2011-12, released this week.
The cost of the renovation project has soared since 2005, when Treasury Board approved $769 million to restore the building.
In February 2011, the Public Works Department said the cost had grown to $863 million - what was then an increase of $94 million.
The same day the government revised its initial estimate, former auditor general Sheila Fraser said she "would not be at all surprised if the cost estimates increase over the project."
Now the public accounts document shows the latest estimate for the whole project is $1.17 billion.
However, Public Works and the office of the minister in charge of the department insist the cost of the renovation work itself remains the same - and the billion-dollar estimate simply factors in other costs, such as moving MPs' offices to other buildings.
The repairs to the historic, three-storey structure - built in three phases between 1859 and 1906 - involve masonry restoration, removal of asbestos, seismic upgrades and a new roof and windows. The work is scheduled to be finished by 2017.
The billion-dollar estimate for the West Block project does not include a separate, $425-million renovation of the Wellington Building across the street from Parliament Hill.
In its 2012-13 report on plans and priorities, Public Works said that by March 31, 2011, "all major projects were all on schedule and on budget." The department reiterated that statement Thursday.
Public Works says there have been no increases to the approved budgets for the parliamentary precinct projects, including the West Block.
"The public accounts include the estimated costs of various projects," spokesman Sebastien Bois said in an email.
"It is important to note that the estimated costs indicated in the public accounts are updated annually to include projects that are underway as well as new approved projects."
He added the West Block work involves other costs, such as temporary accommodations and rehabilitation projects for other buildings, "and as a result the changes to amounts that appear in the public accounts reflect the projects that have been added over the years under that umbrella."
New Democrat MP Linda Duncan said she doesn't have a problem with the renovation itself, but she wants to be sure that taxpayers don't get stuck with the bill if the cost rises any further.
"I don't think it's an outrage that we are renovating historic buildings. I think Canadians would appreciate that," she said.
"I think what Canadians would be deservedly outraged about is everybody's being told to cut back. One would have expected that this government would have managed a contract where the cost overruns are not borne by the Canadian taxpayers."
The West Block figure in the public accounts also includes work on the former Bank of Montreal building, now called the Sir John A. Macdonald Building, which is estimated at $99 million, Bois said.
"This addition explains the difference between the costs published in the public accounts over the last year," he said.
Liberal MP Justin Trudeau, raised at 24 Sussex Dr. when his father was prime minister, said the government should preserve historic buildings, rather than spending money to add more seats to the House of Commons.
"It's an interesting question; it's one that I certainly reflect on personally as I look at what's happening to my old home in 24 Sussex, which is slowly crumbling around its present occupants," Trudeau said.
"But because of a political climate that is saying that, 'Oh no, you know, we can't spend on certain things, except we're willing to add 30 more MPs that nobody wants to the House of Commons.' There's a lack of priorities that we're seeing in Ottawa."
The West Block renovation has been a lightning rod for controversy.
The RCMP is investigating the relationship between Montreal company LM Sauve and long-time Conservative supporter Gilles Varin.
Company owner Paul Sauve says he paid Varin $140,000 to help him win a $8.9-million contract to restore part of the West Block in 2008. Varin says he only got $118,000 for his work.
Sauve's company went bankrupt a year later and lost the job.
Last year, the government awarded PCL Constructors Canada a $358.5 million contract to manage the West Block restoration.
Another company, EllisDon Corp., was awarded $209 million in contracts to repair the Wellington Building and the Sir John A. Macdonald Building.
However, Public Works brought in PricewaterhouseCoopers this month - at a cost of $112,608 - to do a financial audit of "contractual payments and compliance with specified tendering procedures" in relation to construction management contracts for the West Block, the Wellington Building and Sir John A. Macdonald Building.
The auditors must submit their findings by the end of next March, although Public Works has the option of extending the contract by up to five years.
Public Works said the PricewaterhouseCoopers audit has nothing to do with the cost of the West Block renovation project.