10 Downing Street has two things: mice and a chief mouser. For more than a decade, an officially recognized feline has kept the residence’s rodent infestation to a minimum.

Over a similar period, the official residence of Canada’s prime minister has seen an unchecked explosion of rodents.

Nests and vast quantities of feces were found throughout 24 Sussex, the 35-room mansion overlooking Ottawa. They took over the attic, basement and crawl spaces. Decomposing carcasses filled the walls of the decrepit building.

Now, prime minister Mark Carney has announced a competition for the country’s leading architecture firms to revive the storied building “to a standard worthy of the country that it serves”.

The Royal Architectural Institute of Canada will design the framework and bring together an independent jury of experts in architecture, heritage conservation and design, which will recommend the winning design to cabinet.

“24 Sussex Drive will be built by Canadians for Canadians,” Carney said on Friday, telling reporters that the winning design would be announced on 1 July 2027: Canada Day.

“At a time when much of the world is buffeted by crisis, Canada’s history, our institutions and our traditions matter more than ever,” he said, standing outside the uninhabitable building. The prime minister said that while foundations of identity largely take the form of language, culture and laws, buildings can stand as testaments “made of timber and stone … in which we recognize ourselves”.

Originally named Gorffwysfa (Welsh for “the place of peace”), the sprawling estate has housed 11 prime ministers since the government took it over in 1951. But its shortcomings have long plagued heads of government.

Jean Chrétien, prime minister from 1993 to 2003, brought reporters to witness the need for buckets to catch rainwater from a leaky roof. Only after a storm blew off sections of the roof did he finally get the needed repairs.

“It’s a symbol of the public office of the head of our federal government and of the democratic traditions that office represents. And yet it has not been cared for with the respect that it deserves,” he said. “Now it’s in critical condition.”

Years of negligence have left the official residence of the prime minister plagued with mold, cracked windows, failing plumbing and an electric system widely seen as a fire hazard.

In 2023, National Capital Commission (NCC), the group tasked with preserving heritage buildings in Ottawa, shut down the residence because of the voluminous safety hazards. The following year, it said it had stripped away the asbestos, mold, lead and rodents carcasses, leaving the building empty but with an estimated C$40m cost to fully renovate and upgrade. On Friday, Carney said it was difficult to estimate a cost because much of that would rely on the final design.

Last month, former governor general Mary Simon, whose term recently same to an end, said it was inappropriate for a prime minister to live on the grounds of Rideau Hall.

But Rideau Cottage, the a 158-year-old building meant originally for the secretary of the governor general, was chosen out of necessity for former prime minister Justin Trudeau and his family, given the inhospitable state of 24 Sussex.

Carney has continued the tradition, residing at Rideau Cottage.

Carney told reporters that while the 24 Sussex has long been a symbol of the country, it “must also be a home, and the women and men who will lead our country in the future will need a residence for their families”. He was adamant that he would never live in the residence, given the starkly contrasting timelines for reconstruction and politics.

“I and all public officials are stewards of the offices we hold. We don’t own them. We serve them to serve Canadians and we have a responsibility to leave things better than we found them.”

Legendary architect Moshe Safdie, who envisioned many of the country’s most acclaimed buildings, will chair the jury assessing design plans.

“It’s an extraordinary site with extraordinary potential,” Safdie said. “Something wonderful can be developed here.”