A proposal to restore the Christ Church Cathedral would be the cheapest option for saving the building, Restore Christ Church Cathedral spokesman Mark Belton says.

"Cost is not mentioned in the report but there have been some statements going around that the cost wouldn't be much off $100 million. There have also been indications from engineers that it could be much less that that," he said.

"It is the least costly option for restoration. Obviously to take it down and built it all up again is going to cost more than keeping bits of it there. Important parts like the roof aren't even badly damaged."

Belton was in full support of the "excellent" proposal from a panel of leading engineers, whose plan involved replicating an underground mine.

The Great Christchurch Building Trust, chaired by former MPs Jim Anderton and Philip Burdon, yesterday provided The Press with a report that it claims proves "maximum retention" was feasible and could be achieved without any safety risks.

"It proves definitely that the cathedral can be saved and it meets all safety requirements," Belton said.

"This report has been prepared independently by respected engineers. There can no longer be any debate as to whether there is a viable engineering solution for maximum retention of the cathedral."

Belton hoped the Anglican Church would seriously consider the proposal.

"I hope they will be encouraged and emboldened by this report to work through the retention option."

Anglican Church spokeswoman Fiona Summerfield had her phone switched off this morning, with a message saying she usually worked between 1pm and 5pm.

Prime Minister John Key told TV3's Firstline programme this morning that although the Government thought the cathedral was a "great building", their advice was that the building was unsafe and needed to be demolished.

"Effectively what the Government has said is that on the best engineering advice we've got, the Anglican Church probably have no option but to demolish the church and the cathedral. So what we are doing is making sure that deconstruction is done in such a way that we preserve as much material as we can."

Key thought the focus should be on a replacement for the cathedral.

"If our engineers tell us the cathedral is unsafe and needs to be demolished, we can't just step in and say it's okay because a few people like it. It's not practical. The focus should be on what will replace the cathedral and maybe can we incorporate much or part of the old cathedral. That might be a good compromise though."

A press conference will be held by The Great Christchurch Building Trust at 1pm today to discuss the report.

WHO WILL PAY?

Anderton did not expect ratepayers or taxpayers to fund the restoration.

Overseas donors were keen to offer financial support, but not for ''any old building'', he said.

''They want this building restored and if it is, they're going to front up with some hard cash.''

WHAT IS THE PLAN?

Structural engineers Adam Thornton, Robert Davey and Stefano Pampanin were commissioned to provide an independent review after it was decided the cathedral should be demolished down about 2 to 3 metres high.

A metal "safe-haven", referred to as the primary shield frame, would be constructed inside the quake-hit cathedral to allow bracing and strengthening work.

"In simple terms, the process would follow underground mining or tunnelling methodology whereby a shaft is shored and strengthened as progress is made ... and workers do not have to venture beyond an already constructed safe haven," the report said.

Last night, an Anglican diocese spokeswoman said the cathedral project team was not available to provide comment on the contents of the report.

Anderton yesterday told The Press the report contradicted views the cathedral could not be safely restored.

"No-one yet has provided a detailed methodology to do it - until now," he said.

The trust was formed to champion the city's threatened landmarks, but the cathedral's imminent demolition forced it to act, Anderton said.

The engineers had worked pro bono and their companies were not directly involved.

Their report was an "objective view" of whether the building could be made safe and restored mostly intact, Anderton said.

"We didn't tell the engineers what we wanted. We said, 'Here's the questions', and if the answer had come back, 'forget it, it's gone for all money and it's going to be too dangerous and too expensive', that would have been it."

The review did not include costs, or a rebuild plan, but further investigation would be done if backed by Anglican church officials.

Discussions with Earthquake Recovery Minister Gerry Brownlee and church officials had been "collegial", Anderton said.

"As far as the trustees we've been dealing with, we've had goodwill. They've met with us and are still considering it," he said.

"This document does put a line in the sand in terms of these loose statements that the building can't been made safe. That is not true, it can be [made safe]."

The Canterbury Earthquake Recovery Authority (Cera), which issued the section 38 demolition order, was only interested in safety, Anderton said.

"The engineers are saying, 'If you want to restore this building, you're better off doing it with as much of the building intact as you can'.

"If the will is to restore it, that's the best way to do it. We're trying to work through with the church whether they really want to restore it."

Brownlee is overseas and was also unavailable.

EXPERT SUGGESTS A DIFFERENT WAY

The current method being used to pull down the Christ Church Cathedral may not be the safest, engineers say.

Wellington structural engineer Adam Thornton and University of Canterbury associate professor Stefano Pampanin, president of the New Zealand Society for Earthquake Engineering, yesterday released a report that offers an alternative to existing plans, which would see building taken down to about two to three metres.

Thornton, whose expertise was seismic strengthening and temporary support and bracing, questioned whether taking the cathedral down "slate by slate, stone by stone from a man in a bucket in a crane" was the safest option.

"We are concerned that once they start demolition, there will come times when it's not safe to put a man in a bucket and those areas will have to be knocked down, which perhaps eliminates the possibility getting out the artefacts," he told The Press yesterday.

"More importantly, from a common sense point of view, we soon came to the view that a much greater part of the building could be retained than what was being planned."

Thornton's "building in building" method protected workers by using a metal frame – moving it through the church while walls and columns were braced and roof rafters reinforced.

"If there's an aftershock or something is thrown off, the people working are protected," he said.

Italian-born Pampanin said deconstruction would not have been used in his country.

He felt it was safer to have a steel bunker than to have unshielded workers near the building.

The steel frame method was widely used, but often not for damaged churches because their roofs were prone to collapse and entry could be gained through the top.

"Here, the roofs are there and we'd better use them. It's fantastic news that the roof, or the diaphragm, is there," Pampanin said.

"Instead of cutting what is strong, we're simply coming from underneath so the building in building approach makes a lot of sense."

- © Fairfax NZ News