Director at Austral Archaeology David Marcus said they were commissioned seven months ago to uncover the history that lies underneath the footprint of the new development.

Mr Marcus said they had begun their report and discovered the land was originally purchased in 1855 and passed through several owners. At the time Brisbane Street wasn't considered a main road and no one wanted to develop the site.

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In 1859 the land was passed over to John Skully, a local constable who built a cottage, which Mr Marcus said from later maps is likely to be under the current court building.

Mr Skully owned the land until his death in 1860, when it was bought by brothers, Thomas and Martin Manning in 1874.

Mr Marcus said he believed in 1875 the brothers built extra buildings which were rented out, where the new courtroom will be built.

"The current courtyard pretty much matches the footprint of an 1874 cottage that was rented out," Mr Marcus said.

"It was there for about 10 years, then the land was resumed for the court house, the cottage was demolished and the present building was constructed.

"So my job is to just make sure as we're going through the construction work that if we find anything related to that cottage, I'm on hand to record it and manage impacts."

Mr Marcus will systematically, using a small machine, lower the ground and take out deposits one-one-by-one. The artefacts will then be taken, cleaned, thoroughly recorded and analysed. Afterwards the materials will be available to be displayed at the court house.

The archaeologist said he's hoping to uncover post holes from the original building and footings the timber cottage was built on.

"If I'm really, really lucky there's going to be what we call an under floor deposit, which is all of the material that the people living in the house were using. If they dropped it, it would fall through cracks in the floorboards and so we would find under the floor a centimetre or two, all of this rich artefact material," Mr Marcus said.

It is expected the excavation process will take between three and five days.

"It's always exhilarating to be on site and to actually find the building we knew was there and to find the traces of people who lived in the building," Mr Marcus said.

"It's even more amazing when you're on an excavation like this and you find the things you're not expecting, it's always a thrill, maybe less so for the developer."