KEY POINTS:
One of the first experts to predict a leaky homes crisis says it could affect owners for another 20 years - and cost more than $11 billion to fix.
Greg O'Sullivan, from building surveyors and remedial design company Prendos, warned of a "potential timebomb" in 1994.
This week
he described the situation as "dynamite".
"It's worse than I predicted. We realised things weren't being built decently or certain cladding types were not performing.
"The crazy thing is, even with that knowledge, they [building authorities] allowed the introduction of untreated timber. That didn't kick in until '98. That's when the avalanche occurred."
O'Sullivan blamed failings throughout the building industry for the crisis.
But he levelled particular criticism at the forestry sector, which he said introduced untreated timber to save money. He said he couldn't understand why the Government and Building Industry Authority allowed it.
"You could only buy untreated timber, the market was flooded with it. Builders were told by the industry and forestry groups it was as durable as anything.
"We started finding much more voracious rots that attacked timber very, very quickly - within seven months of a house being built. We'd never seen that before."
The crisis also failed to surprise former consulting engineer John Lello, who saw similar problems in Canada in the 1960s.
Until the middle of the decade projects had to comply with precise contract specifications, the National Building Code, building acts and other legislation. That clear procedure was "wrecked" in 1965 by a "permissive" building code and other legislation.
"Contractors welcomed the opportunity to increase profits by using cheaper, untested materials and easier methods."
Lello said there had been many problems with leaky buildings, particularly on Canada's wet West Coast.
He said the "political and technical blunder" in New Zealand was difficult to understand because the Canadian problem was well-known.
Prime Minister Helen Clark this month confirmed the Government's long-held position that it was not responsible. It had set up the Weathertight Homes Resolution Service and would make no further financial contribution to the repair bill.
National leader John Key said the resolution service was bureaucratic and, if elected, his party would investigate a streamlined approach that may get Government funding.
Both Lello and O'Sullivan reject the Government's denial of responsibility.
Lello wants the Government to take responsibility for a previous administration's changing building legislation and to award costs and apologise to homeowners.
O'Sullivan said New Zealanders would be living with the legacy of leaky buildings for another two decades, not just in private homes but in public buildings.
There was a strong stigma attached to monolithic cladding-style homes and building standards had deteriorated so much that even repairs were failing.
"Lots are being done poorly. They will fail again. There are reports which come across my desk which freeze my heart. You can't help but feel sorry for the people involved."
Homeowners and Buyers Association president John Gray agreed that poor building practices were an important factor in the crisis.
He had seen such basic mistakes as tradesmen overlapping building paper the wrong way round, allowing water to leak in behind it.
"It's bad design and bad workmanship. Monolithic cladding doesn't just fail, it's the way it's installed."
Gray also blamed shoddy council inspections for allowing such bad workmanship.
"The level of negligence around council inspections is just frightening."