Ardern denied the policy was doomed to fail.
"The alternative is do nothing and continue to having a declining home ownership rate and I don't accept that."
She said KiwiBuild was ambitious and no government had tried to bridge the gap in the affordable housing market as hers was doing.
National's housing spokeswoman Judith Collins said it was time for Housing Minister Phil Twyford to face the facts.
"You've had builders, academics, the Treasury, Reserve Bank, MBIE, economists and media commentators all pointing out the serious flaws in his policy, and saying the Government won't deliver on its promises, in spite of Phil's 'Hear No Evil' approach to his responsibilities.
"And today it's the Salvation Army urging Phil to accept he's not up to it and calling on the Government to bring in the experts to deliver more houses," she said in a statement.