Nearly four years after Justin Trudeau opted not to move into the prime minister's official residence over concerns about its crumbling state, the building in Ottawa remains vacant — except for staff using the kitchen to prepare meals for Trudeau and his family.

It appears no decisions will be made on the future of the residence until well after the fall federal election.

The federal Conservatives accuse the Trudeau government of dithering over "critical" upgrades to the stately yet rundown home, and needlessly costing taxpayers more money in the process.

At the same time, none of the main federal party leaders appears willing to opine on whether the building should be torn down or renovated, or whether they would live in the residence if it were upgraded.

Asked by The Canadian Press their preferences for what to do with the building if elected — or re-elected — to office, the Liberals referred all questions to the National Capital Commission (NCC), which oversees dozens of properties in the capital region; the New Democrats did not provide a response and the Conservatives referred to the project as just one more Liberal blight under Justin Trudeau's leadership.

"The renovation costs of 24 Sussex Drive are a failure that Justin Trudeau has been unable to fix in four years," Conservative Leader Andrew Scheer's spokesperson, Daniel Schow, said in a statement.

"The NCC has estimated that it will cost nearly $100 million to renovate 24 Sussex and other official residences. This is an unacceptable situation, and unfortunately, taxpayers are being stuck with the bill."

Scheer, if elected prime minister, would "look for innovative ways to break through the red tape and the overregulation that has created this debacle," said Schow.

The Conservatives would not say, however, whether Scheer would elect to live at 24 Sussex should he become prime minister this autumn. Scheer is living in another building managed and maintained by the NCC; Stornoway, the Official Opposition leader's residence.

24 Sussex is in 'critical' state: NCC

Prior to being defeated by the Liberals in 2015, Conservative Prime Minister Stephen Harper lived in 24 Sussex Drive for a decade, but would not approve any spending on the building beyond necessary or emergency repairs.

Harper was warned by then Auditor General Sheila Fraser in a 2008 report that more than $10 million in repairs were needed just to make it safe to inhabit.

No one expects the NCC to decide the fate of the building until after the October election, said David Flemming with Heritage Ottawa, which wrote to the prime minister in March calling for the creation of a non-partisan committee to decide what to do with 24 Sussex.

Heritage Ottawa made clear in that letter that it prefers the building be renovated, not demolished.

"Please do not condemn this fine building to landfill," the letter stated.

The Prime Minister's Office has not responded to the letter, Flemming said.

In a report prepared in April last year, the NCC classified 24 Sussex as being in a "critical" state of disrepair.

The report assessed the building's replacement value at $38.46 million. At the same time, it determined the cost of maintaining the structure at nearly what it's worth: $34.53 million. That figure did not include necessary upgrades to security and grounds maintenance, nor repairs to the nearby pool building, which the NCC described as "rotting."

The home, built in 1868 by American-born lumber baron and member of Parliament Joseph Merrill, has suffered decades of neglect since it was expropriated by the government in 1943. It last underwent major renovations in 1951.

Its outdated wiring risks causing a fire, the drain pipes regularly clog, the exterior stonework is crumbling and the building is filled with asbestos, the NCC was told last year.

"The building systems at 24 Sussex have reached the point of imminent or actual failure," said the report.

Beyond renovations, it has been costing taxpayers nearly $228,000 annually, on average, just to operate and maintain the property, the NCC said.

Trudeau, who lived at 24 Sussex as a child when his father Pierre was prime minister, acknowledged in an early 2018 CBC interview that anyone agreeing to spend anything on the house risks the wrath of the electorate.

"No prime minister wants to spend a penny of taxpayer dollars on upkeeping that house."

At that time, Ontario Conservative MP Erin O'Toole said the party would only consider supporting renovations and repairs once Trudeau had repaid the costs of his trip to the Aga Khan's island home in 2017.

To date, no options for dealing with 24 Sussex have been formally presented to the NCC, spokesperson Jean Wolff said recently.

The kitchen in the house is still being used almost daily. When Trudeau and his family are in Ottawa, staff there prepare meals and deliver the food a few hundred metres down the road to a cottage behind Rideau Hall where the prime minister, his wife and three children have lived since shortly after being elected.

Watch: Tories tied support for 24 Sussex reno to Aga Khan back in 2018

Conservative MP Erin O'Toole said his party will only back the costs for renovating 24 Sussex drive if Trudeau pays for all costs associated with his trip to the Aga Khan's island home. 0:25

Former Liberal prime minister Paul Martin has argued 24 Sussex is a historical landmark that merits preservation. Kim Campbell, who was prime minister for four months in 1993, has suggested it be knocked down.

So has former prime minister Joe Clark's wife, Maureen McTeer. She argued in 2015 the building lacks architectural value and should be bulldozed and replaced with a building that could show off Canada's best architects and designers.

But her suggested timeline — making it a Canada 2017 project to mark the country's 150th anniversary — passed by with no action taken.

The building is designated a heritage site in Ontario by the Federal Heritage Building Review Office.

But that designation wouldn't prevent the federal government from demolishing the building, said Flemming.

"They could tear it down."