As The Sydney Morning Herald disclosed in November, the building was slated to have opened last year, but the fire hydrant system governing water pressure in the sprinkler system had to be belatedly upgraded for $385,000.

The site at Castle Hill was originally a botanical research station for the museum, growing eucalypts for their oils. From the 1970s, the museum began storing some collection items on site, later sharing its facilities with the Australian Museum and Museums of History.

The new building sits next door to this Museums Discovery Centre where Ultimo’s Locomotive No. 1 will be stored. A six-metre-high giant glass window will give public views into the ground-level large objects storage area where the monorail carriages and other transport bodies rest.

Some 56 staff will be based at Castle Hill, researching, preparing exhibitions, and conserving the collection as a base just 12 kilometres from where the Parramatta Powerhouse opens next year. Thirty-six conservators, curators and registrars are to be relocated from Ultimo.

Acting assistant general secretary of the PSA, Siobhan Callinan, said management had notified the union they expected staff to report to work at Castle Hill from Tuesday.

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“We won’t direct members not to go to Castle Hill at this stage but are extremely concerned at the lack of flexibility for moving staff, the ongoing work, health and safety issues - we will refer these to SafeWork NSW - and the lack of respect for the process. We are considering our options.”

The temporary closure of Ultimo for three years while renovations were undertaken was contested by critics, including the PSA, who claimed that the museum was shut prematurely for cost savings.

The risk assessment by HVH Group found only minor issues and the building was compliant with all regulations and safe for occupation. An occupancy certificate has been issued.

“This new building designed by Lahznimmo Architects will enable for the first time all the Powerhouse collection where it’s not on show at Parramatta or Ultimo to be consolidated on-site and colocated with the Powerhouse collections team,” Powerhouse chief executive Lisa Havilah said.

“It also enables us to extend this site in terms of it being a place of production, for research, for learning, for programs. Parts of the collection have been here since the 1950s. It just means that it’s now all together.

“What’s really special is that this is the only piece of cultural infrastructure in the Hills District and the Hills District is such a fast-growing, important part of the city.”

The new facility contains state-of-the-art facilities including a photographic studio to digitise some 120,000 objects from the collection, a small objects store for ceramics, glass, and metalwork, and a secure store for antique guns and precious jewellery.

Exhibitions will rotate every six months, the first Alchemy showcasing natural dyeing practices in Indigenous communities in the remote Northern Territory. The building will be open to the public on weekends, and during the week for scheduled tours.

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