He has raised concerns with the Reserve Bank and is worried the speed limit could reduce the supply of new houses, making the policy counter-productive.
No one is sure just how many new homes are bought by low-deposit borrowers and first-home buyers. Quinn thinks it might be 15 per cent, although the Reserve Bank thinks it might be closer to 10 per cent.
Some builders of more affordable homes say up to half their buyers are high-LVR borrowers.
Given about 20,000 new homes are built each year, the speed limit may reduce the number of homes by about 3,000 a year.
"If it's all in Auckland, then that's really counter-productive for the policy."
A fall in new-home building would also complicate the Government's housing strategy.
Finance Minister Bill English defended the speed limit this week, saying it was necessary for financial stability.
He argued moves to increase housing supply would help first-home buyers, even though he cited Reserve Bank advice that the speed limit could force up to 8,000 first-home buyers to delay or downsize their plans.
But if a policy designed to control house-price inflation contributes to it by restricting supply, the Government has as big a problem as the Reserve Bank.
One factor driving economic growth is a surge of construction, and Quinn would like to see first-home buyers who are building new homes exempted from the speed limit. The bank may be open to an exemption that increases housing supply.
In a bulletin this week, it said its policy was open to tweaks. It may have to get tweaking.
