Housing Minister Phil Twyford has responded to claims he "has no idea what he's doing", saying he always knew it was going to be "tough" fixing up the mess National left behind.
The Government's KiwiBuild scheme doesn't officially kick off until July 1, but both Opposition leader Simon Bridges and National housing spokeswoman Judith Collins got stuck in to the policy over the weekend.
Ms Collins told Newshub the fact some KiwiBuild homes will be bought from private developers was proof Mr Twyford "can't actually do anything himself".
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"What he's trying to do now is get the private sector to come in, show him how it's done and then try and claim credit for their work."
Mr Bridges told The AM Show on Monday Mr Twyford's latest move - to supercharge New Zealand's prefab industry - shows he "can't do 100,000 houses".
"Don't get me wrong - there's nothing wrong with prefabricated houses, and it may actually be a good idea. But this is a guy who started this stuff, KiwiBuild, in 2012 - and he still hasn't worked it out."
While the Government has often accused National of nine years of neglecting housing, Mr Bridges said Mr Twyford has overseen "nine months of incompetence".
Mr Twyford told The AM Show he "always expected it would be tough".
"We inherited a housing basketcase - some of the most expensive housing in the world relative to local incomes, record homelessness and 71,000 houses short. That's what we inherited from the last Government.
"Now we're determined to turn that around. It's complex, there are a whole lot of obstacles and we are working through them, step by step."
He said overseas, the cost of building a prefab home is about half that "standard" build cost in New Zealand, which has risen 30 percent in the last decade.
But don't expect the rising cost of a KiwiBuild home to reverse course and get cheaper.
"It's very early days. It would take I think probably several years to get one of these factories up and running."
Presently, only a few hundred prefab homes are built each year, says Mr Twyford. The Government is in discussions with "investors both here and overseas" to see if there's interest in beefing that up.
"This is something the New Zealand Government hasn't done for decades."
Despite a lack of firms and workers here, Mr Twyford says there are no plans to manufacture the homes offshore.
"One of the very attractive things about offsite manufacturing is because you're using technology and automation, you don't need such a big workforce."
Mr Bridges says while he doesn't believe the answer is a massive Government building - or buying - programme, he's open to keeping KiwiBuild if it proves it can work.
"If we saw that there was something that was working, you know, we'd do that and many other things... At the moment, you'd have to say it doesn't look good."
He thinks the answer lies in reforming the Resource Management Act, but said National lacked the numbers in Parliament to do that before it lost last year's election.
A Bill reforming the Act was actually passed in April 2017 with the support of the Maori Party. At the time, the Ministry for the Environment called it the most comprehensive package of reforms to the RMA since its inception 26 years ago".
Then-National leader Bill English said in September last year he wanted to remove urban planning from the RMA, saying the Act hadn't been good for growing cities.