The historic front doors of the Old Parliament House - now known as the Museum of Australian Democracy - were engulfed in flames after anti-vaccine and sovereign citizen campaigners deliberately set the facade alight during their December 2021 protests.

The fire destroyed the museum's portico and caused substantial damage to the entrance.

Smoke and soot contaminated all three levels of the building and water used to put out the flames soaked through the front steps and top landing.

The museum closed for four months as staff tackled millions in damages.

"The damage - including smoke, soot and water - was extensive," outgoing museum director Daryl Karp wrote in the latest annual report.

"Although covered by insurance, the estimated $5.3 million restoration cost is substantial."

The museum's team of conservation-trained cleaners painstakingly scrubbed walls, floors and ceilings and cleaned 2800 items from the heritage furniture collection, 2000 Hansard volumes and 5000 props.

A construction crew rebuilt the entry and installed a new fire suppression system but the burnt remains of the 100-year-old front doors loomed large over the project.

"When the flames were extinguished and the smoke dispersed, a charred black wound was all that was visible where the doors had stood," the Old Parliament House annual report stated.

The doors were transported to Sydney for evaluation.

Though the outermost layer was "beyond restoration" and most of the fittings and ornaments required replacing, the rest of the wood was virtually unharmed thanks to the jarrah timber's resilience.

Conservation experts removed the burnt sections, stabilised the internal wood and replaced unsalvageable parts in an attempt to replicate and reinstall the original facade by the end of the year.

They also took steps to protect the building from future incidents by re-tiling and waterproofing heritage areas.

The majority of Old Parliament House reopened in April but the building's facade and Senate chamber remain closed for ongoing restoration work.

In the four weeks after the reopening, the museum hosted 23,000 visitors, mostly Australians who cast their vote in the 2022 federal election.

"Despite the challenges, and with parts of the building still inaccessible to visitors, we remain firmly positioned as a must-visit museum in Canberra," Ms Karp wrote.

Australian Associated Press