Auckland Council has been told to take another look at how many new homes the city's suburbs can absorb under new planning rules.
Two members of an expert group have questioned the council's latest figure, which show relaxed density rules in the proposed Unitary Plan make it financially viable to build 150,400 homes.
Patrick Fontein and Adam Thompson, who helped develop the development capacity model, are concerned with some of the assumptions and judgments used by the council.
After hearing the concerns, the Unitary Plan independent hearings panel has directed the council to work with Mr Fontein and Mr Thomspon to re-run the model.
"Given the importance of these capacity forecasts for the panel's consideration of the residential topics the panel wishes to have clarified the extent to which the assumptions and judgments critiqued by Patrick Fontein and Adam Thompson impact on the capacity forecasts," the panel said in a memo issued on Friday.
Mr Thompson said the latest figure of 150,400 new homes in the residential zones of the Unitary Plan was potentially a bit on the high side.
One reason, he said, was the council had set a relatively high price of $1.05 million for a medium sized house on a small section.
Setting a lower price may not be as commercially viable and lead to fewer homes, Mr Thompson said.
"The point of the model is to test the commercial feasibility of the development," he said.
The model was first tested in July this year and showed 64,400 new homes could be commercially viable in the plan's residential zones.
Since then, the council, developers and an influential community lobby group have agreed to removing density and other controls in the widespread mixed housing residential zone.
There are also suggestions that parts of the single-house zone could be rezoned for multiple townhouses, apartments and studios.
Deputy Mayor Penny Hulse was perfectly happy with the directive to redo the numbers and provide the panel with up to date figures.
But she said issue should not be totally focused on house numbers, but building a good Auckland with good urban design and providing housing choice.
Councillor Dick Quax said it was important for the council's latest modelling to be peer reviewed.
"It is important because if we don't get these numbers right we are condemning future generations to having no ability to own their own home," he said.
In coming weeks the council will release new maps to councillors and Local Boards chairs showing the changes.
The maps will also show which pre-1944 areas and houses qualify for heritage character protection based on surveys by the council.
Waitemata Local Board chairman Shale Chambers said elected members only have three days to review the maps and discuss changes.
"This is less than satisfactory and not the way to get the best outcome for Auckland," he said.