More questions have been raised over the state of Wellington's buildings following the news Defence House will be demolished.

Building owner AMP Capital said the damage sustained in the 7.8 November 14 earthquake is not economically viable to repair. 

New Zealand First defence spokesman Ron Mark says it's the older buildings which seem to be holding it together after the earthquake, leading him to wonder whether some architects and engineers know what they're doing.

"How is it these buildings are fine, yet have to be strengthened and have to have hundreds of thousands of dollars spent on them, and the Defence House and other government-occupied buildings around Wellington - which are new - are being demolished?"

He said he would expect the modern Wellington building to withstand an earthquake centred in the South Island.

Meanwhile, preparation work to earthquake strengthen Wellington's Town Hall is finally getting underway.

The Town Hall, located in Wellington's Civic Square, has been closed since November 2013.

Earthquake strengthening was meant to begin then, but the cost ballooned and work was halted.

This week, exploratory ground testing work is starting to check ground conditions to help guide the design of the building's new foundations.

And work will also begin this week on the council's Civic Administration Building, which closed following last November's earthquake.

Temporary props are being installed to allow controlled access into the building.

A decision on its future isn't expected to be made for some months.