Three-bedroom "affordable" homes on the market for $650,000 under Phil Twyford's Kiwibuild programme would be out of reach to more than half of Aucklanders, a study from the city's council suggests.

A study from the Auckland Council's chief economist looked into home affordability in country's biggest the city.

As well as finding that middle-income earners had been the hardest hit by declines in housing affordability, it suggested a three-bedroom home at the top end of the price range of the KiwiBuild scheme is likely to be out of reach for half of Auckland's households.

KiwiBuild aims to build 50,000 homes in Auckland in the next 10 years. The caps on the costs of KiwiBuild homes in Auckland are $650,000 for a three bedroom house, $600,000 for a two bedroom and $500,000 for a one bedroom. Twyford said the Government hoped it would be able to secure them for less than that in some areas. A spokeswoman this afternoon stressed the $650,000 was the maximum price for these homes.

The council said that its study discovered a household would need to be making $105,200 a year - in the top half of income earners - and already have a 20 per cent deposit in the bank to afford a KiwiBuild home at the $650,000 cap.

If a household only has 10 per cent deposit, the council says a family would need to earn $118,300 a year to afford a $650,000 KiwiBuild home.

"To deliver houses that even households in the top half of earners could afford, Kiwibuild would need to deliver a lot of houses below the $650,000 cap," council senior economist Harshal Chitale says.

The council's chief economist unit also says Auckland's squeeze middle-income earners have been hit the hardest by worsening housing affordability in the city.

It said median housing prices in the country's biggest city increased 71 per cent 
from $494,000 in 2012 to $847,000 in 2017.

Median household income was up by 25 per cent over that time, $78,100 to $97,300.

Chitale said because mortgage interest rates were almost identical in 2012 and 2017 differences in affordability were "driven purely by changes in house prices and household incomes".

According to the council's analysis in 2017, the poorest third of Auckland households 
"had practically no likelihood of being able to purchase a freehold home (whether a stand-alone house, townhouse or apartment) - even with a 20 per cent deposit".

A household squarely in the middle of the pack could only afford a home in the bottom 11 per cent of the market (537,000 and below), provided they had a 10 per cent deposit.

If they had a 20 per cent deposit, they could afford a property in the bottom 18 per cent of the market.

"We also examined how affordability by income percentile has changed over the five years since 2012. Practically every household income group saw the range of houses they could afford fall sharply," Chitale says.

"But the biggest declines were for households in the 50th to 75th percentiles. These middle-class income groups have been increasingly locked out of home ownership," he said.