The natural response to a natural disaster is to see that it cannot cause as much damage next time. But if the disaster is as rare as a major earthquake and the remedy would remove most or all of our older buildings, does the risk warrant it? That is the question we need to pose in response to proposals from the royal commission of inquiry into the Canterbury earthquakes and a review of the building code by the Ministry of Business, Innovation and Employment.
The royal commission recommended that local bodies should be required to identify all earthquake-prone buildings in their jurisdiction within two years and that the owners be given seven years to either bring them up to the standard or demolish them. The ministry has suggested slightly longer periods - five years for the councils to identify the buildings and 10 years for the owners to strengthen or remove them. The later deadline is the one the Government has adopted for the purposes of an important public discussion.
It is time to think carefully about the costs - not just to building owners but to the community if heritage is lost - and to weigh the costs against the risk of damaging earthquakes. The risk is very low. The building code in force since 1976 requires new buildings to be able to withstand a magnitude of earthquake likely to occur maybe once in 500 years.
The ground forces that hit Christchurch on February 22, 2011, were much greater than that, equivalent to an earthquake reckoned to occur once every 2500 years. Nobody has suggested we need build to that standard of resistance. Ultimately, there is no such thing as an "earthquake-proof" building. A shallow quake in unfavourable rock structure can generate much greater shaking than its magnitude normally causes.
That is what happened in Christchurch and the question should be asked: is the aftermath of such an event really the best time to be deciding the fate of our built heritage?
Neither the royal commission nor the ministry has suggested raising the new building standard or the definition of "earthquake-prone buildings", those assessed to be less than a third of the standard.
They simply want all those buildings brought up to at least a third of the standard.
The Auckland Council has told the ministry that a 10-year notice would be an "execution order" for the city's areas of special character and heritage. It would prefer that building owners be given 15 years to comply, but even that might be a death warrant for the character of places such as Mt Eden and Devonport.
It needs to be remembered that most of those who died in Christchurch's February aftershock were not in or near the unreinforced masonry buildings that so concern the royal commission. They died in recently constructed blocks that ought not have collapsed. Considering the numbers on Christchurch's inner city footpaths that day it is remarkable more were not killed by falling parapets and glass.
The lessons we can learn from disasters are not just about avoiding risk, they also provide a better assessment of it. Low risk is not no risk but low risk means it might be worth taking rather than losing other things of value.
The royal commission was critical of city councils that operate what it calls a "passive approach", identifying buildings at risk but not requiring owners to bring them up to standard unless they want to do alterations. Considering Auckland's risk, that still seems a sensible approach.
The consequences of what is proposed could be worse than an earthquake.