Property investors are to blame for New Zealand's high house prices, a new research paper published by the Helen Clark Foundation says.

Author Jenny McArthur said a "decades-long boom in property investment" had driven up housing and land prices to create "windfall gains" for property owners, the real estate sector, and banks.

The Helen Clark Foundation is an independent public policy think tank located at the Auckland University of Technology. The report has been published with the intention of stimulating debate on housing issues.

McArthur said previous attempts to address housing problems had not worked because they saw it simply as an issue of supply and demand.

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But she said the windfalls for those in the property market had come at the expense of families and people's basic need for shelter.

BRADEN FASTIER/STUFF Property investors are to blame for New Zealand's high house prices, a new research paper says.

Speculation in the market was the primary driver of house price growth, she said, and houses were being treated as an investment, fuelled by the availability of cheap credit.

To address that, she recommended debt-to-income limits on borrowing for high-income households and a capital gains tax.

That would reduce prices, she said, but the Government could help those who were pushed into negative equity - where they owe more than their houses are worth - by refinancing a proportion of each of the existing mortgages of people's primary homes.

To help those locked out of the market in the short-term, the report recommends boosting the supply of genuinely affordable homes through state-led delivery of leasehold housing for management by hapū or community land trusts.

CHRISTEL YARDLEY/STUFF Author Jenny McArthur said previous attempts to address housing problems treated it simply as an issue of supply and demand.

She said the current situation was failing younger generations, single-parent households, Pacific Islanders, and Māori.

To help address that, the report recommends targeted funding, finance, and capacity development for developing papakāinga on Māori land.

It also suggests that urban planning should identify places where the market cannot provide affordable housing and deliver it directly with Urban Development Authorities (UDAs), transferring the completed homes to hapū or community land trusts.

"Policies to curb speculation, including the bright-line test and foreign buyer ban, have not sufficiently addressed the problem of local investors who are actively bidding up prices," the report said.

"The present situation is socially and economically unsustainable, with profound impacts on health, education and social cohesion," McArthur said.