The Sirius building in the Rocks should be preserved for its aesthetic value and rarity, the Heritage Council says.

In a decision made public this month, the council said the building's association with the Green Bans movement in the 1970s added to its rarity, and it therefore would be a loss for the state were it torn down.

"It was a unanimous decision of the Heritage Council that the building had aesthetic significance and it also represented rarity in its design and form," council chairman Stephen Davies said.

The council's recommendations are, in the majority of cases, accepted by the Minister for Environment and Heritage.