Immigration bosses have defended plans to spend more than a quarter of a billion dollars overhauling their Canberra headquarters.
The department wants to spend $255 million slashing the number of buildings its holds in the national capital from 12 to five and shifting its main digs to a new building alongside Canberra Airport.
Department officials expect the move will save some $324 million in leasing costs over 30 years, but Labor Senator Kim Carr is worried the project's price tag does not represent value for taxpayers.
Senator Carr questioned whether it would be cheaper for the federal government to buy - rather than rent - the centrepiece building.
The department did not factor this possibility into its cost-benefit analysis, drawing a flabbergasted response from the Labor senator.
"It strikes me as extraordinary. We are spending this amount of money, but (we do not know) how much savings would there be if the commonwealth owned the building and did not pay the rent," Senator Carr told a Senate estimates hearing in Canberra on Monday.
"You will be in a building for 30 years and it will cost nearly $3 billion. How much would it cost to build the building and not pay the rent? Surely that was part of your cost-benefit analysis."
Immigration boss Michael Pezzullo said a federal government policy to rent rather than own office buildings had stretched back several decades.
But Mr Pezzullo said whichever way one looked at consolidating the offices, the move represented a saving for taxpayers.
Senator Carr also questioned the cost per square metre of the new offices, which is expected to come in at $2063, several hundred dollars more than the $1200 to $1800 government average.
The higher-than-usual costs were associated with its 24-7 operations, the department said in response.
