A debating chamber and a civil defence emergency bunker are part of the ex-Auckland Regional Council building above Spaghetti Junction which the authority is gradually abandoning.

The ARC's headquarters were in a 10-level stronghold at 21 Pitt St, formerly Vodafone House.

But with local body amalgamation, the authority no longer needs the 17,229sq m $52 million building near the top end of Hobson St above the motorway.

Building owner Kiwi Income Property Trust announced this week the ARC was leaving.

"The Auckland Regional Council will vacate approximately 10,700sq m of space in the building between June and October 2011, as its operations are absorbed into the new Auckland Council. It will vacate a further 2200sq m of space on January 31, 2015," Kiwi said on Monday.

An Auckland Council spokesman said this was one of the few buildings the amalgamated council planned to abandon. Most other buildings owned by territorial authorities would continue to be owned and tenanted by the council, he said.

But often staff working at one authority would be shifted into another part of the city so that by Christmas, about 1000 people will have moved. Others would have been moved by around April, he said.

"We're centralising certain parts of the operations. The ARC building is the only one being let go as far as I know," the council spokesman said.

Chris Gudgeon of Kiwi said the empty areas had been leased to engineering firm Beca. Kiwi struck a new nine-year lease on about 14,000sq m of office space at 21 Pitt St, where Beca was consolidating its Auckland operations from three locations, he said.

But Kiwi's win is another listed landlord's loss. Paul Duffy, chief executive of DNZ Property Fund, announced Beca's departure.

"Beca has renewed its lease at DNZ's property at 132 Vincent St for a further two years and one month with notice that it will vacate after this period, March 2013," Duffy said this week.

Over on Pitt St, Beca is examining new uses for old spaces.

Gudgeon said Beca had plans for the former ARC debating chamber and it would use that for conferences or large meetings.

Gudgeon was initially unaware of any disaster cell beneath the building but he made inquiries.

"They do have a 300sq m civil defence facility or a room more than a bunker. They will continue to lease this until 2015," Gudgeon said.

* Owned Kiwi Income Property Trust.
* Construction completed 1990.
* Kiwi bought it in March 1997.
* Was 75 per cent leased to state tenancies.
* Soon, Beca will expand there.