Harold Cosier and Jenny Dixon, who bought the historic West Wollongong house early last year, have lodged plans with Wollongong City Council showing a large-scale renovation project to transform the run-down building into a grand family home.

The documents include plans to reinstate the Bukari Street mansion's Georgian balconies, which were removed in earlier renovations, and build a separate modern extension to preserve the original building's structural integrity.

When Ms Dixon and Mr Cosier bought the property last January, the internal staircase had been removed to divide the mansion into two flats, and years of "unintentional neglect" and unsympathetic renovations had transformed it into a boxy grey structure.

Ms Dixon said the restoration had since become an expensive passion project, describing how it had taken on a life of its own.

"This old house has got its own entity ... I quite often catch myself talking to it and it's almost like it shares things and has its own surprises," she said.

"Like, when we were scraping paint off a wall, we went down about three layers and found a little crayon drawing done by a little kid. I love those surprises and memories of everyone else who has been there."

This strong attachment to the house's history has led to a costly but integrity-driven restoration.

According to plans lodged with the council, the family has proposed the demolition and removal of various additions and changes, which have been made over the past 170 years.

These include the modified verandahs, the external staircase, a single-storey kitchen, bath and laundry area and outdoor features.

This will make way for the restoration of the original verandahs, driveway, internal fireplaces and a late-Victorian era staircase.

"Anything that is original that we can save, we're saving, and we're also trying to reinstate what was in the original building," Ms Dixon said.

"The original craftsmanship is just so magnificent that I couldn't, in good conscience, not restore it."

The delicacy of the old structure, and a desire not to introduce invasive systems into a house built before electricity and plumbing, led to plans for a modern addition, allowing the property to be used as a modern family home.

According to the proposal, a two-storey extension would be built at the back of the original residence including a loungeroom, dining room, kitchen, laundry, powder rooms, bathroom, master bedroom and ensuite.

"For us to put a real bathroom in the house would have required significant engineering and would have compromised what was there originally, but we still need to be able to live there in a modern way," Ms Dixon said. "So all the bathrooms and the kitchen will all be in the new bit, so we won't be impacting on the old building with water in any way."

The plans are on exhibition until September 5.