The quake-damaged Wellington headquarters of the New Zealand Defence Force and the Ministry of Defence is to be demolished.

Defence House, also known as Freyberg House, has been closed since soon after the 7.8 earthquake that slammed the northeastern half of the South Island and the lower North Island on November 14.

In a press release this afternoon, the defence force announced the Aitken St, Thorndon building's owner, AMP Capital, had told them Defence House would be demolished.

This decision was made following investigations in the extent of damage to the seven-storey, 11-year-old building and what would be required to fix that damage.

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"AMP Capital advises that the building can be repaired but that the cost of repairs is not economically viable.

"As Defence House does not present any immediate health and safety risk, the demolition will be completed by deconstruction - meaning that the building will be taken apart in a controlled manner."

Since the quake, affected defence force and ministry staff have worked out of the Freyberg Building, which is immediately behind Defence House.

By the end of April about 900 staff will be based in Freyberg Building.

Long-term accommodation options in Wellington for both organisations are being considered, the statement said.

"The loss of Defence House will be sad for the NZDF. However, our people are what makes a headquarters, and we continue to work together to deliver for the NZDF and for New Zealand."