The Prime Minister's Wellington home is getting a $1 million upgrade this month, the Department of Internal Affairs (DIA) has confirmed.

Premier House – the Prime Minister's residence when she is in Wellington – will be receiving "important" remediation work as part of a "routine" property upgrade, according to a DIA spokeswoman.

It is understood part of the sum will be used on an upgrade to a perimeter security fence.

On Friday, DIA said it would be doing remediation work on Premier House from mid-October.

The department manages Premier House on behalf of the Government.

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"A periodic assessment in June 2017 identified some important remediation maintenance work to be addressed to ensure the property is fit for purpose," it said in a statement.

But today, after questions from the Herald, the department revealed the $1 million price tag for the maintenance work.

"This is part of a routine property upgrade, as part of DIA's ongoing asset management processes, including budget allocation," DIA said in a statement today.

The officials said the assessment was initiated by the previous Government after it "identified parts requiring important upgrades in building matters."

"The essential work will ensure the quality of the property is preserved and that Premier House is fit for purpose given that it is the official residence of the Prime Minister of New Zealand and a venue for hosting guests from other Governments," the Spokeswoman said.

Premier House has been used as the official residence of New Zealand's Prime Minister since Parliament was moved to Wellington in the 1800's.

It underwent a major refurbishment, which was completed in 1990, DIA said.

The department said it has engaged with mana whenua, the Thorndon Historical Society, the Thorndon Residents Association and Heritage New Zealand to maintain the heritage of the property and neighbourhood.