Take a peek at Canada’s largest-ever heritage restoration project

It's a fixer-upper like no other that's entering its most challenging phase, according to federal officials who took journalists on a tour of Parliament Hill's Centre Block renovation.

"This is the most technically complex part of the project, so we are laser-focused on getting this right," said Rob Wright, an assistant deputy minister for Public Services and Procurement Canada.

Now that construction crews are almost done removing hazardous materials and storing more than 20,000 heritage assets and artifacts, they can begin the challenging work of building a sprawling underground visitor centre and reinforcing a structure that dates back between the late 1910s and 1920s.

Crews have dug and blasted about 23 metres into the bedrock beneath the base of the Peace Tower. The new three-floor basement will be home to the new Parliament Hill visitor centre and other functions.

The Senate's suspended plaster ceiling with hand-applied gold foil has been left in place, while many of the artifacts and furnishings inside Centre Block have been catalogued, removed and stored.

Among the heritage assets tucked away for safekeeping are the building's heritage lighting fixtures and its stained and leaded glass windows. Some of them, which have been restored, were on display during Thursday's tour, illuminating a gutted House of Commons chamber shrouded in scaffolding.

Crews are also busy outside the historic structure inspecting, cleaning and repairing each of the building's approximately 365,000 sandstones that form the exterior of the iconic Gothic revival building.

One of the primary focuses of the work over the next couple of years will be reinforcing the Centre Block's foundation, making it resistant to earthquakes. Parliament sits within a seismically active zone.

Approximately 500 base isolators — giant shock absorbers — will need to be installed. But in preparation for the complex task, 800 temporary posts will be drilled to support the structure so the base isolators can be installed.

Centre Block's heating and cooling system is also being modernized. That's thanks to a geothermal system, new windows and other energy retrofits that will make it carbon neutral in a country that has net-zero climate ambitions by the year 2050.

Federal officials say the project, which is expected to be completed by 2031, will bring a century-old symbol into the next era.