Editorial: Quake work needs limits and balance

Photo / Brett Phibbs

Last September, the Dean of Christchurch, Peter Beck, breathed a huge sigh of relief and thanked the Christchurch City Council for investing in earthquake strengthening 10 years earlier. The work had helped Christchurch Cathedral emerge almost unscathed from the first of the earthquakes to hit the city.

On February 22, there was no such escape. The spire and entire corner section of the cathedral are now rubble. Steel girders have splintered and bear nothing of the Australian hardwood beams - an earlier measure to strengthen the structure - they once held.

The fate of the cathedral is instructive. It says something about the limits of earthquake-proofing old and heritage buildings, a subject of heightened concern not just in Christchurch but throughout the country. An event such as this removes complacency and gets people thinking about preparing for the next major emergency. They want to know what lessons can be drawn.

The Prime Minister has indicated an inquiry will centre on "why so many lives were lost" on this occasion. Inevitably, much of the focus will be on the way some older buildings collapsed, giving their occupants little chance of escape.

A similar climate prevailed after the 1931 Napier earthquake. This led to the country's first building code four years later. It recommended standards of design and construction so that buildings could resist earthquakes.

Since then, successive codes, in 1965, 1976, 1984 and 1992, have introduced compulsion and developed the structural performance criteria, accommodating changes in materials and design as they went.

The 2004 Building Act, for its part, dictated that an owner's change of use of an older building would be the trigger for earthquake strengthening, the extent of which would be determined by local authorities.

The adequacy of this framework is now being questioned. Some engineers want new and tougher standards that will make the significant quake-proofing of all older buildings compulsory.

They point to the several older structures in Christchurch that failed to meet the goal of the current regulations in the event of a large earthquake. These seek to protect life by ensuring a building will not collapse and people can escape from it, even if the structure, itself, is seriously damaged.

Notable failures were the 1972 CTV and 1963 Pyne Gould buildings. They numbered among buildings too old to be affected by the important 1976 code. Most had also not been altered, and had not, therefore, been subject to strengthening.

Mandatory quake-proofing of all New Zealand buildings would, however, be hugely expensive. Proponents say this would be worthwhile if even one life is saved, let alone the hundreds lost in Christchurch. But the need for preparedness must be balanced so as not to be out of all proportion to the degree of risk.

In the aftermath of such an event, there can be a heightened sense of alarm, which triggers a desire to do whatever is required to prevent a repeat, no matter how extreme or costly. A lesson of Christchurch Cathedral is that whatever the precautions, a set of circumstances can render them ineffective.

On balance, therefore, it seems reasonable to retain the status quo on older buildings, and insist on earthquake strengthening only when they are being modified.

It would, however, be very useful if homeowners were advised individually how earthquake-resistant their houses were. They could then decide whether to strengthen or sit tight.

It would also be helpful, as the United Future leader, Peter Dunne, suggests, if earthquake-prone buildings were publicly listed. People should know the status of buildings they live in, work in or use often.