Cost a factor in rebuild
Christchurch developers are shying away from using base isolation technology, which protects buildings against earthquake damage, as they seek to reduce costs.
The use of base isolation spiked at the start of the Christchurch rebuild but has dropped off as developers try to limit costs to attract tenants with affordable rents.
Estimates put the cost of a base isolated system at about 5 per cent of the total build price. In quake-prone Japan, base-isolated buildings are rented and sold at a 10 per cent premium, which pays for the additional engineering costs.
Beca technical director of earthquake engineering Dr Richard Sharpe said some developers did not want to pay the “very small premium”.
“People always think about cost, and not about the value and, hell, we know after Christchurch the value of being able to get straight back into a well-designed building is enormous,” Sharpe said.
Sharpe said his company was putting “our money where our mouth is” in using base isolation for the four-storey Triangle Centre in the central city.
Colliers general manager Jonathan Lyttle said in Christchurch there was a “severe kneejerk reaction” after the quakes to new building requirements.
Few buildings built after 2004 were damaged beyond repair in the February 2011 quake, he said.
“Did we need [new technology] and was there a market here that could actually afford them? I think the answer is no.
“There’s quite a few intangible benefits that one only sees if you get a [magnitude] 7.0 [quake], but one pays for a very long time.”
Engineer John Hare, of Holmes Consulting Group, believed the initial rush to install protective engineering solutions was a “marketing push”.
“There seems to be some sort of implicit assumption that the only way you can reduce damage is by using all sorts of expensive technology, when something like simplifying the form of the building and using good, basic design techniques will go a long way to reducing damage in the event of an earthquake,” he said.
Property developer Richard Diver said base isolation seemed a good option in the right circumstances, but it was expensive.
However, he was taking seismic precautions on his Victoria St buildings, including drilling piles as deep as 24 metres.
WHAT IS BASE ISOLATION?
Base isolation dampens the motion in a seismic event to protect contents and elements in a building, enabling it to remain functional after an earthquake.
The rubber-bearing technology used in many base-isolated structures was invented in New Zealand in the 1970s, coming out of work done by the Department of Scientific and Industrial Research in Lower Hutt.
Wellington has nine good examples of base isolation including Te Papa and the retrofitting of the Parliament buildings.
- The Press
- Alan Wood & Marc Greenhill