"The Government will pull every lever at its disposal to increase the supply and affordability of housing," he said.
Fletcher Building's chief operating officer for housing Steve Evans said height limits meant only 500 homes could be built if the quarry was filled to the level of Mt Eden Rd, whereas the Fletcher plan to "cascade" down 15 to 17 metres below street level would allow more homes to be built.
"We are using the topography of the quarry to provide density that no one really sees," he said.
Dr Smith's move to join the case is the first time an Environment Minister has used this power since 1999.
Surprisingly, Environmental Defence Society executive director Gary Taylor welcomed it.
"Arguably the Government's view on resource consent applications ought to be more routinely put before the Environment Court on appeals," he said.
"But that hasn't happened for ages, so this is new and obviously the Government is concerned about community groups thwarting intensification in Auckland, and that is a valid planning concern.
"It will be up to the court to decide what weight to attach to his submission and any evidence that he might call."
Professor Dick Bellamy of the South Epsom Planning Group, one of the two groups that have lodged appeals, said he also welcomed the Ministry for the Environment being involved in housing issues.
Garry Bryant, president of the other appellant Three Kings United Group, said the two groups did not oppose housing on the site but simply wanted it to be environmentally sympathetic.
"We object to it because it will allow them to build up against the base of the Big King," he said. "You don't build up against the side of volcanoes, it's time it was stopped."
Mr Evans said that if the court approved the project, he hoped work would start before the end of this year and the first 200 apartments would be ready by 2018.
He said pricing would depend on demand and size, with apartments ranging from one to four bedrooms, but the company was already building apartments on the edge of the quarry priced below $450,000.
He said the whole 1500-unit project would take eight to 10 years to build.
Three Kings Q&A
Q. What is Fletchers proposing in Three Kings?
A. Up to 1500 homes, mainly apartments cascading down from street level into a disused quarry to between 15 and 17 metres below the surrounding land.
Q. Why are local groups appealing?
A. They want the quarry filled to roughly the surrounding land level and less intensive housing with more open space next to the Big King mountain, Te Tatua a Riukiuta.
Q. Why is Nick Smith intervening?
A. He says the appeals would mean long delays and fewer and dearer homes which would be too little, too late to help Auckland's housing shortage.
Q. What happens next?
A. Dr Smith hopes the Environment Court will hear the appeals before mid-year. Fletchers says building could then start this year with the first 200 apartments ready by 2018.
