Although staff are moving back in, it could be months before earthquake-repair work is completed on the near-new BNZ Harbour Quays complex on the waterfront.
Engineers are still working out how to fix the top floors on two of the building's three piers where ceilings collapsed under the weight of unrestrained air conditioning ducts and sprinkler pipes.
Ceiling panels fell on trading room desks in the 6.5-magnitude quake which rocked Wellington on Sunday, July 21, last year.
Nobody was hurt but burst pipes caused extensive water damage throughout the building, soaking carpets and getting into electrical wiring.
BNZ Wellington recovery manager Richard Griffiths said about 1200 staff, or about 90 per cent of Wellington staff, would be back in there by April.
But getting the last 100 staff back would be delayed while work was completed on the two top floors.
Delays were caused by debate over work required to meet minimum codes and incorporating lessons learned from the Christchurch quakes.
Griffiths said the BNZ wanted sprinkler pipes, ducting and ceilings throughout the building to be installed to the latest standard but engineering this was complicated by the fact that the top floors on two of the building's outer piers were designed differently to the rest of the building.
The top floor on the middle pier is capped by a concrete pad while the top floors on the first and third piers were steel framed and had higher roof cavities, which meant they were prone to move more in a quake.
This has added complexity to the process of installing and bracing building services.
Griffiths said a key lesson from the Christchurch and Wellington quakes was building structures and fitouts needed to be designed collectively.
"The history of what we've found with New Zealand construction is they haven't been designed collectively as an entire system."
This was borne out in Christchurch where buildings performed structurally as they were designed to, but their fitouts failed.
Griffiths said they were still working out costs of repairs and other expenses, including the lease of office space in other buildings around the city for months before bank staff could return to Harbour Quays.
However, the bill is expected to run to more than $10 million.
Centreport, which owns half the Harbour Quays building, last week reported its earthquake damages bill was $12m.
A big part of this was for repairing Harbour Quays. The $100m building opened in 2009. Centreport then sold a 50 per cent share of its ownership in the BNZ and neighbouring Customs and Statistics head office buildings to the Accident Compensation Corporation.
The repair project is being managed by Miyamoto Impact and the work is being done by Fletcher Construction.
- The Dominion Post
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