Three Wellington streets pose greatest risk of facade collapse, engineers say

The Reading Cinema car park in Wellington had to be torn down after it was damaged in the November 14 quake last year. Photo / Mark Mitchell

Three streets in Wellington, including the popular Cuba St Mall, have been singled out as the riskiest spots in a major earthquake and most in need of urgent repair.

Engineers have warned the Government that there is "low public awareness" of the potential for a large aftershock to cause building facades to collapse in these locations.

In a report released today by the NZ Society for Earthquake Engineering, they said commercial and retail areas in Riddiford St, Newtown, Cuba St, Te Aro and Jackson St, Petone were "of greatest concern".

"The Societies believe that ... we need to motivate owners to carry out securing of facades in the interests of public safety and the avoidance of a possible repeat of the loss of life that occurred in the February 2011 earthquake," the report said.

The advice has prompted the Government to require building owners in "high-risk" regions to secure unreinforced balconies, parapets or chimneys within a year.

That is a dramatically shorter timeframe than the existing 15-year deadline to bring all earthquake-prone buildings up to code in Wellington.

However, building owners will be assisted by Government and council subsidies which will pay up to half the cost of remedial work. Their repairs will also be exempted from resource and building consent requirements if a qualified engineer oversees the work.

The new deadlines and subsidies will apply only to regions most at risk of an aftershock following the Magnitude 7.8 earthquake in Kaikoura on November 14 - Wellington, Lower Hutt and Blenheim.

Around 300 buildings will be affected by the rules, most of them in the capital. Tenants or workers are unlikely to be forced out for the repairs, the Government said.

Announcing the new policy in Wellington today, Building and Construction Minister Nick Smith said: "These are the kinds of buildings that killed 39 people in the February quake [in Christchurch]."

Getting all building owners to secure unreinforced structures urgently was "the prudent response", he said. While the costs were high, the renovations significantly reduced the risk of fatalities after a quake.

The estimated cost of the repairs is $9 million, or between $20,000 and $30,000 per building. Of that total, $4.5m will have to be covered by building owners, while the Government will pay $3m and councils will pay $1.5m.

The policy comes after GNS Science advised the Government that Wellington's quake risk was eight times higher than normal after the Kaikoura event. It would not return to normal for three years, GNS said.

The Government's move was welcomed by councils and engineers.

Structural Engineering Society president Paul Campbell said that while shorter, stiffer earthquake-prone buildings were not affected by the Kaikoura earthquake, they still posed a significant risk.

"Every earthquake is different - and earthquakes don't test all buildings equally," he said.

"On 14 November, as the earthquake waves travelled through rock away from Kaikoura, high frequency waves dissipated as heat.

"But low frequency waves experienced less resistance and reached Wellington. These low frequency waves created resonance in mid-height buildings, causing severe shaking.

"The next earthquake could be quite different and it's important that earthquake-prone buildings are dealt with."