"That is clearly unsustainable," he said.
A start on the Papakura project comes as Housing NZ bows out of another long-planned 10ha development next to the Weymouth child welfare home, which the new Social Housing Unit in the Ministry of Business, Innovation and Employment has allocated to "third-sector" social and affordable housing.
The NZ Housing Foundation, which has built shared-equity housing in other parts of Auckland, is believed to be assembling a proposal for what may be 300 to 350 homes.
Auckland Community Housing Network co-ordinator Charles MacCulloch said his members had been asked how many homes each might want in the project.
The Community of Refuge Trust, a mental health provider, was interested in 10 to 20 units.
The Social Housing Unit has allocated $21 million for Auckland providers over the next three years plus $25 million for "specific larger developments and/or possible asset transfer initiatives" which may include Weymouth.
Iwi belonging to the Tamaki Collective, which signed a historic settlement with the Government last month, may also contribute capital for land and development.
"In relation to Weymouth we have an opportunity to be involved and we do want to be involved in a housing development for affordable and social housing," said Tamaki Collective chairman Paul Majurey.
"We are talking to a whole range of folk - those with expertise in social and affordable housing, those with expertise in building, those with expertise in equity finance."
Mr Bignell said earthworks on the Papakura site would start next month and the first houses would be built next year.
Housing NZ's 2012 statement of intent said it planned to sell more state houses than it builds or buys over the three years to 2015-16 to build up money to invest in the following six years.
Over the next five years it plans to sell 1850 houses in Auckland and build or buy 3270, adding a net 1420 homes.
Mr Bignell said the number of Auckland state houses "has gone down a little bit this year" and funding released from those sales was now ready to go into new projects.
"We are now looking to get more homes under way."
Cheap homes
Papakura
*450-500 homes.
*Work starts next month.
Weymouth
*300-350 homes.
*Negotiations under way.