Montreal's City Hall may be beautiful to look at from the outside, but the interior is apparently going to cost an ever-growing fortune to repair.

Built in 1878, the last time the building underwent a major reconstruction was in the 1920s.

Workers in the building have known for years of the problems with plumbing, ventilation, heating, and air conditioning, with some of those who work in the building say that they cannot even close their windows properly.

There will also be work to replace walls and pillars and remove asbestos in certain parts of the building.

The first estimates to repair the building delivered to city executives in 2015 said it would cost $30 million, with a possibility that repairs could go up to $60 million.

But those estimates, and even an estimated repair cost of $72 million reported last month have proven to be woefully inadequate.

On Friday the city of Montreal said the renovations would cost anywhere from $116 to $140 million to transform City Hall into a LEED-certified building.

The city expects challenges with updating a building that's considered a heritage site.

“We have to preserve certain aspect the building during all the work and all the construction and after that to restore them,” said Montreal Executive Committee president Benoit Dorais.

Dorais said the cost was justified because of the sheer scope of the work necessary.

"$140 million I think it's not exaggerated. That's a cost that is in phase with all the problems we have, the heritage questions, and the other problems in the building," said Dorais. “Most of the things in city hall are not at the standard we should expect in 2018.”

Construction is due to begin in 2019 and take three years to complete, with all city hall functions taking place in the nearby Lucien Saulnier building, which itself is being renovated at a cost of $9.5 million.

The interior work on Montreal's City Hall comes just a few years after work on the exterior was finished.

Work on the $10 million copper roof began in 2008, while the city also spent $5 million to update the electrical system and install new lights.